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| Metalworking (rec.crafts.metalworking) Discuss various aspects of working with metal, such as machining, welding, metal joining, screwing, casting, hardening/tempering, blacksmithing/forging, spinning and hammer work, sheet metal work. |
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rack and pinion
The telescope I've referred to in recent postings has a pair of knobs joined by an axis whose center is a pinion that engages a rack on a tube that holds the eyepiece. This enables one to focus the telescope. The rack seems to be well-oiled but still moves somewhat unevenly in some places as one turns the knobs. When I look at it so that I can see all the teeth below me: ||||||||||| it seems that they have not all worn evenly, that some are apparently thicker than others, and that some of the valleys between them are more filled than others. I don't know if the latter condition indicates there is more oil in some than others or whether it indicates the presence of more dirt, which contributes to the uneven motion. The person who loaned it to me told me it would be ok for me to oil it and maybe that also means it is ok for me to clean it (e.g. with a toothbrush). But before I do anything, I'd like to be sure of what kinds of conditions contribute to this kind of uneven motion in a rack and pinion. It mostly turns evenly but in some places it seems more prone to offer some resistance. Leaving aside whether it would be permissible to make repairs on the borrowed scope, I don't know if it is possible to replace the rack. It seems to be riveted in place. I wouldn't know how to select a replacement rack or two replacement rivets. Maybe with suitable machines, I could make my own rack. That is something I would keep in mind for the future, when I have some machines and want to modify or build my own telescope. Continuing with the hypothetical, suppose I want to be really fanatical about figuring out what exactly is wrong with the rack. Since eyeballing it suggests some irregularities, suppose I want to measure all of the heights of the teeth and all of the widths of the peaks and of the valleys. Is there any convenient way to do this? One way that occurrs to me is to take the rack, clean it, ink it and press it against a piece of paper to make a print of the rack. Then I can photocopy the inked page with enlargement and measure it. There would still be a lot of measurements to make, but they wouldn't be so small and easy to mess up. Also, if the print were faint in some places, that would confirm my impression that it was badly worn in some places. There is one other issue related to the rack and pinion. There seems to be no barrier between the rack and pinion and the interior of the telescope tube. It occurs to me that this might let vapors from the oil diffuse into the tube and possibly also coat the inner surface of the telescope lens at the other end. That sounds undesirable and makes me wonder whether someone might have made a mistake by oiling the rack and pinion in the first place. If so, the source of the mistake might have been that someone noticed the uneven motion and resistance to turning, didn't realize the role that wear might have played in it, and instead tried to solve the problem by oiling it without realizing that this might be bad for the optics. On the other hand, I don't know anything about scopes or racks and pinions, so my 'pinions aren't worth anything. If someone is better informed, please inform me. Thanks. -- Ignorantly, Allan Adler * Disclaimer: I am a guest and *not* a member of the MIT CSAIL. My actions and * comments do not reflect in any way on MIT. Also, I am nowhere near Boston. |
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On 27 Nov 2004 02:18:57 -0500, Allan Adler
wrote: Clean the rack and pinion, making sure that there's nothing stuck in the root, the very bottom of the teeth. Uneven wear, or uneven spacing when the rack was made? Either are possible, Rack and pinions are available from Boston Gear, Browning and others. If it's older US made scope, no problem. If it's a newer import, Rotsa Ruck. Accepted lube is RT-44, using way oil or any other substitute is going to guarantee problems with lube migration, or shiny stains where you don't want them. IF you replace the rack, you might be tempted to use the nylon rack, bad idea, I've done it and it didn't take long to switch back to the brass. Rivetted sounds like an import, 0-80 screws are what I use. It ain't rocket science, pretty straight forward job. Helical focuser is also an option, and I've made a couple of those too, each has it's benefits and drawbacks. Personal preference there, neither has a clear advantage over the other unless you're putting a camera on the focuser, in which case the helical is out. |
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Allan Adler wrote in
: big snip You might want to investigate the pinion. There may be nothing wrong with the rack at all. If the center hole on the pinion is offset, or at an angle to the teeth, this would also explain the uneven wear. Even a mis- alignment of the two bores the pinion rides in could cause this. -- Anthony You can't 'idiot proof' anything....every time you try, they just make better idiots. Remove sp to reply via email |
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Anthony writes:
You might want to investigate the pinion. There may be nothing wrong with the rack at all. If the center hole on the pinion is offset, or at an angle to the teeth, this would also explain the uneven wear. Even a mis- alignment of the two bores the pinion rides in could cause this. I ruled out a problem with the pinion on the grounds that the resistance wasn't repetitive as one turned the knobs completely a few times. I don't know if that is a valid argument. The pinion and the knobs form a single piece. So, unless it was made incorrectly, I don't have any reason to suspect the pinion itself. I'm not sure what you mean by "at an angle to the teeth". One meaning might be that it crosses the teeth. With that meaning, it might not work at all, so I'm guessing you mean that the planes containing the teeth of the pinion and of the rack are parallel but the peaks of the pinion are not parallel to those of the rack. To put it another way, I think you're saying that the axis of the knobs might not be parallel to the bottom line of the rack valley it passes through, so that it dips to one side. That is conceivable but again it would seem that it would result in consistent problems all along the length of the rack, not just in one place. On the other hand, there still might be a problem such as you describe. I unscrewed the "box" that covers the pinion. It is not perfectly rectangular, since it has to fit against the cylindrical tube and also it has cuts to allow the axis of the knobs to pass. I turned the box over, so that these cuts were all on top and the box was open, and noticed that there was a flat rectangular piece of metal inside of nearly the same length and width of the box. The rectangular piece had a rectangular hole in it. When I opened it, it was jammed in so as to run diagonally in the box from one edge on the bottom to the opposite edge on the top. There were two more identical pieces of metal sitting flat on the cylinder and the axis of the knobs, enclosing the little towers that the screws screwed into and the pinion. The bottom of the box has four "pedestals", one in each corner. I don't know whether the flat piece of metal was correctly placed. Possibly someone else opened it up to oil the pinion and put the flat piece back in incorrectly and possibly it is really supposed to be in the diagonal position in which I found it. If the three flat pieces are removed entirely, then the axis of the knobs wobbles badly. I think the three flat pieces are intended to sit flat on the four pedestals. When they are stacked that way, they fit in the box but rise to block off most of the hole the knob axis passes through. So, I think the flat pieces are used to clamp the knob axis in a fixed position. The flat pieces also rise above the bottom of the circular arcs that are intended to fit the cylinder body. I think that when the box is screwed back onto the cylinder, the flat pieces are forced down to the bottom of the circular arcs, forcing them to bend to conform more to the cylindrical shape. This has the effect of pushing the other two, still straight, edges of the flat pieces to clamp the knob axis even more tightly. This arrangement makes so much sense to me in terms of the operation of the rack and pinion that I find it hard to believe that the diagonal arrangement I found could possibly be correct, but maybe there is something I don't know, such as the possibility that the diagonal arrangement eliminates some lateral movement. I didn't find that correcting it, even if it was wrong, made any difference in the resistance, but this is all kind of subjective. Unfortunately, I can't see the pinion engaging the rack, so it is hard to know what the problem is exactly, except by trying something that has the effect of curing it and concluding that what I thought I was correcting was actually what was wrong. But I do have one idea: I can count how many teeth there are on the pinion and how many are on the rack and how much of a turn I have to make of the knobs to move a given number of teeth along the rack and how many teeth there are between the visible part of the rack and the part that actually engages the teeth. That means I may be able to wait until I find some resistance and then turn the knobs the appropriate amount to move the bad part of the rack to where I can see it. After I've gotten that crackpot idea out of my system, I'll probably just clean and re-oil it, as was suggested by others. But I'm still concerned about the possibility that oil fumes might be contaminating the telescope tube and coating the inside surface of the telescope lens. -- Ignorantly, Allan Adler * Disclaimer: I am a guest and *not* a member of the MIT CSAIL. My actions and * comments do not reflect in any way on MIT. Also, I am nowhere near Boston. |
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Allan, what if you ask for a digital camera for Christmas?
GWE Allan Adler wrote: Anthony writes: You might want to investigate the pinion. There may be nothing wrong with the rack at all. If the center hole on the pinion is offset, or at an angle to the teeth, this would also explain the uneven wear. Even a mis- alignment of the two bores the pinion rides in could cause this. I ruled out a problem with the pinion on the grounds that the resistance wasn't repetitive as one turned the knobs completely a few times. I don't know if that is a valid argument. The pinion and the knobs form a single piece. So, unless it was made incorrectly, I don't have any reason to suspect the pinion itself. I'm not sure what you mean by "at an angle to the teeth". One meaning might be that it crosses the teeth. With that meaning, it might not work at all, so I'm guessing you mean that the planes containing the teeth of the pinion and of the rack are parallel but the peaks of the pinion are not parallel to those of the rack. To put it another way, I think you're saying that the axis of the knobs might not be parallel to the bottom line of the rack valley it passes through, so that it dips to one side. That is conceivable but again it would seem that it would result in consistent problems all along the length of the rack, not just in one place. On the other hand, there still might be a problem such as you describe. I unscrewed the "box" that covers the pinion. It is not perfectly rectangular, since it has to fit against the cylindrical tube and also it has cuts to allow the axis of the knobs to pass. I turned the box over, so that these cuts were all on top and the box was open, and noticed that there was a flat rectangular piece of metal inside of nearly the same length and width of the box. The rectangular piece had a rectangular hole in it. When I opened it, it was jammed in so as to run diagonally in the box from one edge on the bottom to the opposite edge on the top. There were two more identical pieces of metal sitting flat on the cylinder and the axis of the knobs, enclosing the little towers that the screws screwed into and the pinion. The bottom of the box has four "pedestals", one in each corner. I don't know whether the flat piece of metal was correctly placed. Possibly someone else opened it up to oil the pinion and put the flat piece back in incorrectly and possibly it is really supposed to be in the diagonal position in which I found it. If the three flat pieces are removed entirely, then the axis of the knobs wobbles badly. I think the three flat pieces are intended to sit flat on the four pedestals. When they are stacked that way, they fit in the box but rise to block off most of the hole the knob axis passes through. So, I think the flat pieces are used to clamp the knob axis in a fixed position. The flat pieces also rise above the bottom of the circular arcs that are intended to fit the cylinder body. I think that when the box is screwed back onto the cylinder, the flat pieces are forced down to the bottom of the circular arcs, forcing them to bend to conform more to the cylindrical shape. This has the effect of pushing the other two, still straight, edges of the flat pieces to clamp the knob axis even more tightly. This arrangement makes so much sense to me in terms of the operation of the rack and pinion that I find it hard to believe that the diagonal arrangement I found could possibly be correct, but maybe there is something I don't know, such as the possibility that the diagonal arrangement eliminates some lateral movement. I didn't find that correcting it, even if it was wrong, made any difference in the resistance, but this is all kind of subjective. Unfortunately, I can't see the pinion engaging the rack, so it is hard to know what the problem is exactly, except by trying something that has the effect of curing it and concluding that what I thought I was correcting was actually what was wrong. But I do have one idea: I can count how many teeth there are on the pinion and how many are on the rack and how much of a turn I have to make of the knobs to move a given number of teeth along the rack and how many teeth there are between the visible part of the rack and the part that actually engages the teeth. That means I may be able to wait until I find some resistance and then turn the knobs the appropriate amount to move the bad part of the rack to where I can see it. After I've gotten that crackpot idea out of my system, I'll probably just clean and re-oil it, as was suggested by others. But I'm still concerned about the possibility that oil fumes might be contaminating the telescope tube and coating the inside surface of the telescope lens. |
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On 27 Nov 2004 10:51:04 -0500, Allan Adler
wrote: The shaft for the pinion floats in the "box", and the flat piece inside is the spring that keeps tension on it, keeping it fully engaged. Where the spring contacts the shafts, use a heavy grease, it's slow turning, but needs the lubrication. IF, when the pinion is fully engaged in the rack, the shafts hit the bottom of the slots, the rack is worn out. If it's not repetitive, then the pinion is probably reasonably concentric to the shaft, and the rack is the problem. In the older scopes, wear on the rack would take a very long time, but the newer ones sometimes have plastic rack, or soft brass, which will wear quickly. RT-44 is used because it does not outgass, it stays where you put it. Oil fumes on the mirrors are a legitimate concern, not fatal, but cause for cleaning and collumating more often than they should be. If the rack is worn, there is nothing that will even things out but a new rack. I would be more concerned if there was slop in the drawtube/focuser body fit. This is also compensated for by the flat spring in the "box". The spring should press the pinion into the rack, and also to one side of the slots the shaft runs in. |
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On 27 Nov 2004 11:06:26 -0500, Allan Adler
wrote: It was made in Japan according to the specifications of Meade. I didn't see a date anywhere, but I know that it is at least 10 or 11 years old and probably more. Ok, newer import. But Meade supports their products pretty well, and it might be possible to just buy a new drawtube, with the rack already installed. Is there any convenient way to try to figure out, without damaging the telescope or screwing up its optical alignment, whether any lubrication has migrated into the telescope tube? If it has, is there a good way to clean up the mess inside? Maybe if I don't see any chromatic aberration or haloes, or something like that, when I look at the sky, all is well, but maybe the effects are subtler than that. The biggest problem wouldn't be coating the lens, but causing shiny places on the interior of the tube. It's generally noticable as a loss of contrast, more when looking at a bright object, the moon for example. If it's on the lens/mirror, it *may* cause haloes, or other abberations, but chances of it getting there are pretty slim, especially if the instrument hasn't been relubed with the wrong thing. I clean, relube, recollumate my three reflectors about three times a year, and there isn't too much you can do that isn't field adjustable to correct. If it's a refractor, they're almost impossible to screw up as long as you don't take the lens out of the cell. Once it comes out, unless you mark everything to make sure it goes back in exactly as it came out, all bets are off. Still, all it takes is marking so you know what came out when. Especially the front and back faces of the lens, in a non cemented lens, they can be reversed easily, and then comes the bitch of trying to figure out which one is reversed. A dot of water soluble marker can save hours of frustration. I don't actually know that they are rivets. I only know that when I look at the rack (not brass, by the way, but some grey metal), the brass things I see holding it in place don't look like screws. Could be a zinc alloy, not unheard of. Saves machining at the cost of a longer life. If they were screws, the heads would be instantly seen as such. Play in the rivets is also not unheard of, and sometimes can be frustrating when you're trying to focus that 6mm eyepiece. The higher the magnification, the worse small problems become. (Which is probably why my favorite EP is a 28mm plossl.) |
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Alan:
A couple of simple things you can do to "diagnose" the gear mesh. First thoroughly clean both rack and pinion. Do not polish, but be sure they are clean. Then, do a contact pattern check. This is simply applying some sort of compound to the entire rack and repeatedly running the rack end to end several times and reviewing the "pattern" left behind. Obviously, don't use too much or anything that will get into the optics. Any good grease will do. (On a side note the professional gear guys use colored componds similar to jewelere's rougue.) What you should see ( in a correctly functioning gear mesh) is a uniform pattern on both the rack and pinion through out the entire stroke (all the way round the pinion and full length of the rack). The pattern should be centered on both the rack and pinion and should be as wide as the narrowest member (either the rack or the pinion). You probably will not see a uniform pattern based on what you wrote. If you see the pattern move back and forth across the gears, then you have a misalignment of the pinion shaft (not 90 degrees to the rack). If you see the pattern move deeper and then shallower in the gears then either the rack is warped, or the pinion is ecentric, or you have excessive wear. Use a dial indicator to determine whether you have an alignment problem and deal with it accordingly if you find one. Alsi check to see if the top of either the pinion teeth or the rack teeth is contacting in the root of the mating gear. Rack wear is simple to check. Use a caliper and measure the pitch between any two teeth near either end of the rack (just like thread pitch). If two adjacent teeth are too close for you to measure then simply measure between any convenient number ot teeth (say three or four). Then repeat this measurement several times along the length of the rack paying special attention to the teeth in the middle of the rack. Shorter measurements indicate wear. The pinion can be checked for wear similarly. A helpful trick is to get two short pieces of wire the same diameter (No. 12 copper wire is good enough) and lay one wire in the root of one tooth pair and the other wire in the root of another tooth pair as close to 180 degrees as possible from the first pair. Measure the distance "over the wires". Now repeat this procedure with sucessive tooth root "pairs" all around the pinion You should get the same measurement every time (or real close). Smaller measurements indicate worn teeth. Hope this helps. "Allan Adler" wrote in message ... The telescope I've referred to in recent postings has a pair of knobs joined by an axis whose center is a pinion that engages a rack on a tube that holds the eyepiece. This enables one to focus the telescope. The rack seems to be well-oiled but still moves somewhat unevenly in some places as one turns the knobs. When I look at it so that I can see all the teeth below me: ||||||||||| it seems that they have not all worn evenly, that some are apparently thicker than others, and that some of the valleys between them are more filled than others. I don't know if the latter condition indicates there is more oil in some than others or whether it indicates the presence of more dirt, which contributes to the uneven motion. The person who loaned it to me told me it would be ok for me to oil it and maybe that also means it is ok for me to clean it (e.g. with a toothbrush). But before I do anything, I'd like to be sure of what kinds of conditions contribute to this kind of uneven motion in a rack and pinion. It mostly turns evenly but in some places it seems more prone to offer some resistance. Leaving aside whether it would be permissible to make repairs on the borrowed scope, I don't know if it is possible to replace the rack. It seems to be riveted in place. I wouldn't know how to select a replacement rack or two replacement rivets. Maybe with suitable machines, I could make my own rack. That is something I would keep in mind for the future, when I have some machines and want to modify or build my own telescope. Continuing with the hypothetical, suppose I want to be really fanatical about figuring out what exactly is wrong with the rack. Since eyeballing it suggests some irregularities, suppose I want to measure all of the heights of the teeth and all of the widths of the peaks and of the valleys. Is there any convenient way to do this? One way that occurrs to me is to take the rack, clean it, ink it and press it against a piece of paper to make a print of the rack. Then I can photocopy the inked page with enlargement and measure it. There would still be a lot of measurements to make, but they wouldn't be so small and easy to mess up. Also, if the print were faint in some places, that would confirm my impression that it was badly worn in some places. There is one other issue related to the rack and pinion. There seems to be no barrier between the rack and pinion and the interior of the telescope tube. It occurs to me that this might let vapors from the oil diffuse into the tube and possibly also coat the inner surface of the telescope lens at the other end. That sounds undesirable and makes me wonder whether someone might have made a mistake by oiling the rack and pinion in the first place. If so, the source of the mistake might have been that someone noticed the uneven motion and resistance to turning, didn't realize the role that wear might have played in it, and instead tried to solve the problem by oiling it without realizing that this might be bad for the optics. On the other hand, I don't know anything about scopes or racks and pinions, so my 'pinions aren't worth anything. If someone is better informed, please inform me. Thanks. -- Ignorantly, Allan Adler * Disclaimer: I am a guest and *not* a member of the MIT CSAIL. My actions and * comments do not reflect in any way on MIT. Also, I am nowhere near Boston. |
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#10
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In article ,
Allan Adler wrote: The telescope I've referred to in recent postings has a pair of knobs joined by an axis whose center is a pinion that engages a rack on a tube that holds the eyepiece. This enables one to focus the telescope. The rack seems to be well-oiled but still moves somewhat unevenly in some places as one turns the knobs. When I look at it so that I can see all the teeth below me: ||||||||||| it seems that they have not all worn evenly, that some are apparently [ ... ] I'd like to be sure of what kinds of conditions contribute to this kind of uneven motion in a rack and pinion. It mostly turns evenly but in some places it seems more prone to offer some resistance. [ ... ] Continuing with the hypothetical, suppose I want to be really fanatical about figuring out what exactly is wrong with the rack. Since eyeballing it suggests some irregularities, suppose I want to measure all of the heights of the teeth and all of the widths of the peaks and of the valleys. Is there any convenient way to do this? One way that occurrs to me is to take the rack, clean it, ink it and press it against a piece of paper to make a print of the rack. Then I can photocopy the inked page with enlargement and measure it. There would still be a lot of measurements to make, but they wouldn't be so small and easy to mess up. Also, if the print were faint in some places, that would confirm my impression that it was badly worn in some places. What I would do to examine the rack is to check it on an optical comparator (after a through cleaning, of course). Mount it so you see the rack teeth in profile. Put some clear plastic film under the clips on the display, select the largest magnification you can manage with the optical comparator, and trace the outline of the profile on the plastic film. Now, move to one of the worst teeth, adjust so the bottom of the tooth profile is the same, and trace this one, The area between the two profiles should give you a good idea how badly worn it is. To *make* one, the ideal way (with HSM tooling) would be a horizontal milling machine, a proper gear tooth profile mill (for the rack gear -- which is either #8 or #1 -- I forget which end is correct, but when you buy it you can look that up in the catalog. One end of the set is for 135 tooth through rack, and the other end is 12-13 teeth. Obviously, you first have to know what the size of the rack teeth are -- both diametrical pitch (or "module" for metric gears, IIRC), and the pressure angle. And if the teeth are cut at an angle instead of straight across the gear (more like "/////////" than "||||||||") you will need to angle the blank, and to calculate a correction factor to your feed using a bit of trig to get the tooth spacing to come out right. Note that the angled teeth are a lot smoother in the feed, but you will need better bearings on the pinion, as it will have a side thrust which the straight tooth will not. Now -- if you want to avoid the side thrust, but benefit from the smoothness, then a herringbone gear would be ideal -- but more difficult to make. It would look somewhat like this: / / / / / / / / / / / / / \ \ \ \ \ \ \ \ \ \ \ \ \ There is one other issue related to the rack and pinion. There seems to be no barrier between the rack and pinion and the interior of the telescope tube. It occurs to me that this might let vapors from the oil diffuse into the tube and possibly also coat the inner surface of the telescope lens at the other end. That sounds undesirable and makes me wonder whether someone might have made a mistake by oiling the rack and pinion in the first place. If so, the source of the mistake might have been that someone noticed the uneven motion and resistance to turning, didn't realize the role that wear might have played in it, and instead tried to solve the problem by oiling it without realizing that this might be bad for the optics. The typical lube used in the focusing rings of cameras (multi-start threads) is typically a quite thick grease, and has fairly minimal vapor -- unless it is kept in the direct midsummer sun. :-) On the other hand, I don't know anything about scopes or racks and pinions, so my 'pinions aren't worth anything. If someone is better informed, please inform me. Thanks. Well -- you have most of what I know about the subject above. Good Luck, DoN. -- Email: | Voice (all times): (703) 938-4564 (too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html --- Black Holes are where God is dividing by zero --- |
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#11
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In article ,
wrote: [ ... ] Helical focuser is also an option, and I've made a couple of those too, each has it's benefits and drawbacks. Personal preference there, neither has a clear advantage over the other unless you're putting a camera on the focuser, in which case the helical is out. A double helical -- a tube threaded inside and outside -- one left-hand thread and the other right hand thread, with an inner tube connected to the camera and the outer tube connected to the telescope, and some kind of keyway to prevent rotation of the inner tube relative to the outer tube and you are fine. This is pretty much the way the focusing ring on SLRs is done. (Some older lenses on folding cameras had the front element on a single thread -- but that did not need to move as far to focus through the desired range. Moving the entire lens to focus takes more motion. Good Luck, DoN. -- Email: | Voice (all times): (703) 938-4564 (too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html --- Black Holes are where God is dividing by zero --- |
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#13
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In article ,
wrote: On 27 Nov 2004 22:17:10 -0500, (DoN. Nichols) wrote: A double helical -- a tube threaded inside and outside -- one left-hand thread and the other right hand thread, with an inner tube connected to the camera and the outer tube connected to the telescope, and some kind of keyway to prevent rotation of the inner tube relative to the outer tube and you are fine. This is pretty much the way the focusing ring on SLRs is done. Nope. Focus ring is a nut, with a retainer to keep it from moving, the male thread is on the lens barrel. Usually 4 to 6 lead though, never single lead. Which means there are a lot of ways that it will go together, only one of which is right. That may be the case in the eyepiece focusing on a telescope, and for *some* camera lenses, but the longer the focal length, and the more desire for close focusing, the more likely the camera lens is to be with double helical. I have disassembled lenses of this sort, so I am sure that they exist -- even as short as 135mm focal length on a 35mm camera. The focus ring is tied to the ambisexual ring, with a female thread attached to the camera body, and a male thread attached to the lens cell itself, so you can move the lens cell a long distance without having to have a threaded sleeve the whole length of the travel. Yes, multi-lead makes for faster focusing, and is amost always found in SLRs at least -- and even in the very fine thread on the front element of a Zeiss 75mm f3.5 Tessar on a folding 120/620 roll film camera (16 shots per roll, with that short a focal length -- vertical format by default. That was my first camera with a reasonable quality lens. Suppose a helical focuser for a scope could be made that way, but most of them don't have a real thread as such, it's usually a radiused groove, and engages a ball indent for rapid focusing. I make mine like a very shallow acme thread, the groove just wide enough to take the ball, and deep enough so the ball almost touches the bottom. Parfocal eyepieces eliminate the need for the rapid, but add quite a bit to the cost. There are focusers available in just about any configuration anyone would want, if their wallet is heavy enough. The ball and groove one would work well enough for something light, like an eyepiece, but when you hang the weight of a camera body -- especially if it has a motor drive as part of it for semi-remote shooting -- you need something more sturdy, like a real thread. Enjoy, DoN. -- Email: | Voice (all times): (703) 938-4564 (too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html --- Black Holes are where God is dividing by zero --- |
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Grant Erwin writes:
Allan, what if you ask for a digital camera for Christmas? OK, Grant: Can I have a digital camera for Christmas? (How's that for grantsmanship?) -- Ignorantly, Allan Adler * Disclaimer: I am a guest and *not* a member of the MIT CSAIL. My actions and * comments do not reflect in any way on MIT. Also, I am nowhere near Boston. |
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#17
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In article ,
Allan Adler wrote: It's a refractor. I noticed that, where the lens is, there are 6 screws It's a refractor, and it's borrowed. Two good reasons not to mess with it. The latter because it's very irritating to find that something you've loaned out and mentioned that it would be OK to oil is "rebuilt" without your blessing. Especially if the rebuilding goes awry. The former because I'm about 99% certain that what you are describing (right down to the zinc rack) is a cheesoid "christmas and birthday telescope". The outside of the box prominently tells you it's 200x or 400x, it's got a wobby tripod which may have a low quality "polar" mount, the aperture is a whopping 3 inches or so, etc. These things have probably driven thousands of people away from astronomy. They never work very well, and you should be able to get your own at a junk shop, flea market, recycling center, goodwill or tag sale for very little money. Don't buy one new. You can waste as much time and effort as you would like tearing that apart, without annoying anyone. Don't expect a very satisfying viewing experience. If you actually want a telescope to look at the sky with, get a reflector with a "dobsonian" mount. A physics teaching acquaintance has 2 or 3 of the cheesy refractors (people donate them when they discover that they can't actually see all the stuff they thought they'd see), and one reflector (bought). There's just no comparison, the reflector is that much better - and not really much more expensive if bought new. You can also go the traditional route and grind your own mirror, if you like, or buy mirrors and build the rest of the scope (pretty easy). The mount is easy to build, as well. -- Cats, Coffee, Chocolate...vices to live by |
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#18
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On 28 Nov 2004 02:11:16 -0500, Allan Adler
wrote: You also clean the inside of the telescope tube? As far as cleaning out the spiderwebs, but all I do is run a dry towel through it for that. Mine are all reflectors. I do have a wide field made from a Kodak Aero-Tessar, but that lens is so heavy that I seldom use the instrument, Very difficult to balance it on the mount. The tube is some 20 inches long, not counting the focuser, and balances 3 inches behind the objective lens. Is there a good book that discusses all the things you can do to maintain a scope in good condition? Amateur Astronomer's Handbook, J.B.Sidgwick, Dover press 0-486-24034-7 Also Amateur telescope Making, Ingalls, but it's long out of print, might find a copy at a library. Scientific American Publishing, my copy is copyright 1935. If it's a refractor, they're almost impossible to screw up as long as you don't take the lens out of the cell. It's a refractor. I noticed that, where the lens is, there are 6 screws holding a metal piece that I figure probably clamps the lens in a certain position. The 6 screws are arranged in three pairs, with the three pairs placed 120 degrees from each other. Yes. Antagonistic screws, one will move the lens mount, the threads are in the mount, the other is the locking screw, the threads are in the part that is mounted to the tube. They should be snug, but not tight, excess pressure from them can distort the lens, or in really bad cases, crack it. Also a sign of a little better quality instrument, BTW. Even with the reflectors, collumination is a process of three interactive adjustments, the degree of perfection being dependent on your patience. I have cheaters methods I use in the field, probably not giving perfect collumation, but good enough for casual stargazing. Sidgwick covers it fairly well, but he also goes into making micrometers and other attachments that would require a higher degree of perfection than I do. |
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#19
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On 28 Nov 2004 01:52:42 -0500, Allan Adler
wrote: I would be more concerned if there was slop in the drawtube/focuser body fit. As a matter of fact, there seems to be, if I understand you correctly to mean on the same surface that the rack is mounted to. It is mostly near the rack but "slop" is a good description of it. Ok. On some of the focusers, I don't know if Meade ever used it, there are flat springs opposite the rack, and they furnish friction to keep it from moving unless driven by the rack/pinion. If these are properly set, they will hold the drawtube in a sort of balance with the pressure of the rack, but will seem to be allowing movement, which in use will not be the case. The old 6" Edmonds has two felt strips opposite the rack, some have other methods, even going so far as to having eliminated the rack for a friction drive, and having ball bearings instead of springs or felt. The main thing is that with the eyepiece installed, it should be centered and with the optical axis also centered and parallel to the optical axis of the objective lens. If it was a cheaper focuser, and has the felt, chances are that the felt has compressed and is no longer holding it firmly. Quicky repairs can be made by replacing the felt, but I prefer to use the flocking from the film slit of a 35mm cartridge instead of felt. It seems to not compress as quickly, and sometimes gives a little more "solid" feel to the focuser. When you say "to one side", I think you mean either towards or away from the eyepiece. It should be holding it so the shaft can't move up or down or towards the drawtube easily. If it's too loose, it acts like backlash, or excess play when changing the directon you're moving the drawtube. There are as many variations in how it was accomplished as there are makers of telescopes, every one of them believing they have a "better idea." My own "better idea" would be a planetary drive fine focus knob, but due to the costs of making such an animal, maybe it wouldn't be worth it. I probably have ten or fifteen focusers in different stages of "maybe this will work" in the basement, but still have to come up with the "perfect" idea. It's pretty hard to improve on something that people have been working on for several hundred years. |
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#21
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Ecnerwal writes:
The former because I'm about 99% certain that what you are describing (right down to the zinc rack) is a cheesoid "christmas and birthday telescope". The outside of the box prominently tells you it's 200x or 400x, it's got a wobby tripod which may have a low quality "polar" mount, the aperture is a whopping 3 inches or so, etc. These things have probably driven thousands of people away from astronomy. I doubt very much that there is a telescope that is so bad that I can't learn something from it. Galileo discovered the moons of Jupiter with a much worse scope. Tycho Brahe didn't even have a telescope. Neither did Ptolemy, whose 2 millennium old astronomical contributions are immortal and can still give an amateur plenty of work to do. I may wind up agreeing with you about this scope, but not until after I have made every effort to get something out of using it and examining it. The person who loaned it to me is pretty competent in astronomy and I have a lot of confidence in him. The manual says one can see cloud belts on Jupiter, the Galilean moons of Jupiter, Saturn's rings and some of its moons and lots of details of the Moon. That's not a bad start. Meanwhile, the scope didn't cost me anything and I'm up for the experience of using it, good or bad. Even the low level routine of setting up a scope and finding something in a finder scope and training the main scope on it is more than I am currently competent to do. If I only get that much out of it, and even if the images are lousy, I'll be ahead of the game. Part of finding stuff without computer control is having a certain amount of experience with the general layout of the sky without a scope. That's also something I don't have and I expect I'll get a lot of practice with it trying to use the scope. So what if I can't see anything as long as I walk away from the experience stronger for having tried? That's really all I care about. Which reminds me: is it better to get one dinky Unimat1 now and be able to use all of its component machines, or get the admittedly much better Sherline lathe now and have to wait perhaps several years to get the Sherline milling machine? I'm finding it a tough call, not unlike the issues raised above. If I could get the Unimat1 immediately for free under these circumstances, I would take it and benefit from the experience of using it. It's the same with the telescope. I already go out with binoculars to look at the sky. This scope's a lot better than that. -- Ignorantly, Allan Adler * Disclaimer: I am a guest and *not* a member of the MIT CSAIL. My actions and * comments do not reflect in any way on MIT. Also, I am nowhere near Boston. |
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On 29 Nov 2004 03:19:43 -0500, Allan Adler
wrote: I doubt very much that there is a telescope that is so bad that I can't learn something from it. Galileo discovered the moons of Jupiter with a much worse scope. Tycho Brahe didn't even have a telescope. Neither did Ptolemy, whose 2 millennium old astronomical contributions are immortal and can still give an amateur plenty of work to do. I may wind up agreeing with you about this scope, but not until after I have made every effort to get something out of using it and examining it. Allan, the lens mount you describe rules out a deparment store scope, what you have is a much more expensive instrument. Meade has, and does, import some rather poor scopes, but they also have their higher lines, which are quite good. Here's a quicky test for the mounting of the lens, pick any star, move the focus until you get a blurry dot. If it's round, the lens is mounted square, it it's an oval, the lens needs to be collumated, and the axis that needs adjusting is 90 degrees to the shorter axis of the image. They will interact, and it can be a long and frustrating process to get the dot round. For visual observing, perfection is not needed. Which reminds me: is it better to get one dinky Unimat1 now and be able to use all of its component machines, or get the admittedly much better Sherline lathe now and have to wait perhaps several years to get the Sherline milling machine? I'm finding it a tough call, not unlike the issues raised above. If I could get the Unimat1 immediately for free under these circumstances, I would take it and benefit from the experience of using it. It's the same with the telescope. If you can get one for free, go for it. Don't even think about it, you can learn a lot from the Unimat. For a step up from the Unimat, I would say the Taig, rather than the Sherline. Both have their limitations, but neither of them has an advantage in the quality of the work they can do. The quality of the work depends more on the hands on the machine than on the machine itself. If you can get one with all the attachments, much the better, the only limitation in what you can attempt will be in the size of the work. For small work, and learning purposes, they're excellent little machines. |
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#23
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Donald Nichols wrote: What I would do to examine the rack is to check it on an optical comparator (after a through cleaning, of course). I looked in my optics books and didn't find "optical comparator", so I did a google search and found some information about it. Based on that, I'm wondering whether an old microfilm reading machine I fished out of a dumpster could be adapted for this purpose. It's housing is made of wood, the optics are in metal and it is intended for strips of microfilm, but I did manage to look at some crystals with it. It's a piece of junk but I've been reluctant to give up on it. The point is moot at the moment since it is in storage where I can't get at it, but I expect that situation to change. Even so, I'll need to acquire more practical knowledge about optics than I have at the moment before tackling it. This would be a lot cheaper than buying a comparator, I think, which would probably cost more than a new scope. But I'm looking forward to trying out this comparator idea for checking out the rack. -- Ignorantly, Allan Adler * Disclaimer: I am a guest and *not* a member of the MIT CSAIL. My actions and * comments do not reflect in any way on MIT. Also, I am nowhere near Boston. |
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#25
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"Kelly Jones" described very clearly and in great detail how I could make a thorough check of the condition of the rack and pinion on the telescope. I just have a few questions: Then, do a contact pattern check. This is simply applying some sort of compound to the entire rack and repeatedly running the rack end to end several times and reviewing the "pattern" left behind. Obviously, don't use too much or anything that will get into the optics. Any good grease will do. (On a side note the professional gear guys use colored componds similar to jewelere's rougue.) Is there some kind of common coloring one can mix with with "any good grease" to simulate the stuff the professional gear guys use? For example, how about adding a tiny bit of alizarin crimson or emerald green oil paint to the grease? -- Ignorantly, Allan Adler * Disclaimer: I am a guest and *not* a member of the MIT CSAIL. My actions and * comments do not reflect in any way on MIT. Also, I am nowhere near Boston. |
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#26
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In article ,
Allan Adler wrote: Donald Nichols wrote: What I would do to examine the rack is to check it on an optical comparator (after a through cleaning, of course). I looked in my optics books and didn't find "optical comparator", so I did a google search and found some information about it. Your'e unlikely to find them in an optics book -- but a well-equipped machine shop is more likely to have one. Based on that, I'm wondering whether an old microfilm reading machine I fished out of a dumpster could be adapted for this purpose. It's housing is made of wood, the optics are in metal and it is intended for strips of microfilm, but I did manage to look at some crystals with it. Those tend to have more magnification, and less depth of field than an optical comparator for machine shop work. Also, the screen tends to be a bit awkward to get to to add a transparent sheet to draw on. The one I have apparently came with optional lenses for 10X, 20X, and 40X, but I only have the 20X lens. A proper one has a collimated illuminator, a stage on which the object under test resides (with X and Y motion to move the viewpoint, plus Z for the focus. Usually, there is a way to measure the X and Y motion -- either with big micrometer heads to move the stage, or with dial indicators to measure the motion. However, there are minimal ones which are handheld, including a set of reticles to measure various things including small threads, and angles, an eyepiece, and a tube to join them. eBay auction #3855942073 has a set of reticles, but not the eyepiece and tube. I'm not sure, but I think that the price there is a bit high. Reliable tools has a nice looking one up for auction #3856418973, but it's heavy (300 pounds), and is certain to go higher, as there are over four days left. There is another by Nikon which is still within reason, and it suggests an alternative name "Profile Projector" for the equipment. (Auction #3856039570). I don't see any of the lightweight ones like mine -- it *looks* heavy, but is mostly blown plastic shell and a wood base. The size is necessary to get enough optical length for good magnification. Note that it *will* take up a lot of benchtop space. Try eBay searches for "optical comparator" (with the quote marks) and one will show up sooner or later. A reasonable price is somewhere in the $200-$300 price range. Unfortunately, this type is not there at the moment. Note that the same comparator shows up in the MSC catalog and in sales flyers for significantly more -- reasonable for a business, but not for a hobbyist. The brand on mine is "Micro-Vu", and the one on the MSC offering is Fowler, IIRC. It's a piece of junk but I've been reluctant to give up on it. The point is moot at the moment since it is in storage where I can't get at it, but I expect that situation to change. Even so, I'll need to acquire more practical knowledge about optics than I have at the moment before tackling it. This would be a lot cheaper than buying a comparator, I think, which would probably cost more than a new scope. But I'm looking forward to trying out this comparator idea for checking out the rack. If you want to try to make one, the general design involves: 1) Illuminator on one side of the stage (or below it with a transparent stage). (Plan on something like one of the Quartz Halogen projector lamps in their own parabolic reflectors so you have adequate brightness for good visibility in a well-lit shop. Remember that the more the magnification, the less the brightness remaining. 2) Moving stage for the device under test. 3) Lens to focus the image onto the screen. 4) Angled mirror in the back to bounce the image back and up towards the screen. 5) Round ground glass screen with reference lines (cross hairs plus angle lines and radius lines engraved in the glass, and filled with black paint. 6) Ring surrounding the ground glass screen, with a full 360 degree angle scale on it, and a vernier scale adjacent to it to allow measuring to fifteen minutes or so. 7) Spring fingers (similar to those which hold slides on cheap microscopes. These are used to hold the transparent films, either for hand drawing to compare worn and unworn teeth, or printed in a plotter from a computer, or photographically printed, to compare new parts to their designed profile for quality-control inspection. Good Luck, DoN. -- Email: | Voice (all times): (703) 938-4564 (too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html --- Black Holes are where God is dividing by zero --- |
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On 30 Nov 2004 01:28:24 -0500, Allan Adler
wrote: "Kelly Jones" described very clearly and in great detail how I could make a thorough check of the condition of the rack and pinion on the telescope. I just have a few questions: Allan, as so often happens in this group, most of them have gone off the deep end again. You do not have to do a pattern check on the rack and pinion, that is for precision gearing, and precision gearing is not found in focusers under the $250 range. THe pinion is probably cut from extruded pinion wire rather than being a cut gear. The rack, if it's a gray metal as you describe, is die cast zinc, and no degree of precision there either. It simply is not needed. The optical comparator is massive overkill, just looking at the teeth with a good hand lens will show the problem if it's bad enough to cause a real problem. The racks and pinions in my old Edmonds are now over thirty years old, were never the epitome of quality to begin with, and don't cause any problems in use. If I were using one of the remote focusing units, the backlash might be a problem, but as I focus "eyeball to the eyepiece", it is not. Lube, I lube the drawtube, but grease and oil only attract dirt to cling in the rack, so mine runs dry except for the shaft and the drawtube itself. My final advice, put it back together, take it out and use it. If nothing else, it will give you far better views than the telescopes of Galileo, Herschel, Newton and others. IF the drawtube moves when you turn the knob, it's doing what it's supposed to do. A lot of time can be taken with technicalities, without looking at practicality. And already has, the prime question is "can I get this thing in focus", and if the answer is yes, going deeper into it is only wasting time and money. Your time would be better spent in a dark place, with the scope, even just sweeping starfields to see what is there that you can resolve with the instrument. Have fun. |
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#29
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In article ,
Gunner wrote: On 30 Nov 2004 02:25:01 -0500, (DoN. Nichols) wrote: You're unlikely to find them in an optics book -- but a well-equipped machine shop is more likely to have one. [ ... ] business, but not for a hobbyist. The brand on mine is "Micro-Vu", and the one on the MSC offering is Fowler, IIRC. I have a spare Micro-Vu that Id let go really cheap. Screen is in excellent condition, but the light source was removed for some reason. Power transformer is fine as is the staging. Might be a good place to put on a nice bright LED light source. Or build one around one of the Quartz Halogen projection lamps with built-in reflector. Some of them (usually marked 82 V IIRC) are designed to run from the AC line fed by a single rectifier diode. No big transformer to deal with. But then again, the transformer in the back helps counterweight the optics, stage, and lens at the front. No dial indicators, clamp your own on. Of course -- but provisions for mounting them. I've put a 5" travel one on the X-axis on mine. Out of curiosity, do you know which lens yours has? Enjoy, DoN. -- Email: | Voice (all times): (703) 938-4564 (too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html --- Black Holes are where God is dividing by zero --- |
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Off the deep end? Perhaps. But the original question was about how to
check the rack and pinion, not whether it should be checked. I appreciate you pragmatisism, but it was still fun to describe how to do a pattern check. Whare's your sense of humor?  wrote in message ... On 30 Nov 2004 01:28:24 -0500, Allan Adler wrote: "Kelly Jones" described very clearly and in great detail how I could make a thorough check of the condition of the rack and pinion on the telescope. I just have a few questions: Allan, as so often happens in this group, most of them have gone off the deep end again. |
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On Tue, 30 Nov 2004 18:34:19 -0800, "Kelly Jones"
wrote: Off the deep end? Perhaps. But the original question was about how to check the rack and pinion, not whether it should be checked. I appreciate you pragmatisism, but it was still fun to describe how to do a pattern check. Whare's your sense of humor? My sense of humor disappears very quickly when it goes from the realm of the ideal to the realm of the ridiculous. A patten check on the hypoid diff gears that I used to do by the dozens is one thing, on a rack and pinion, where the rack is die cast and the pinion extruded is senseless. I could have gone into the whole nine yards of a gear lab check, but to what end? In this particular application, if the spur gear has .0002" helix, and the involute error is .001", what's the difference? Even pitchline to pitchline makes no difference here, the pinion is crushed into the rack for full engagement by a spring, and the relation of the pitchlines really don't mean squat. DP of the rack and pinion is going to be probably 32 or finer, you're looking for errors that are going to be in ten thousandths, and even if they're found, they won't bother anything. Even my 35 year old Edmonds, the focusing isn't perfectly smooth, but it doesn't make one bit of difference, it still works just fine. There are some focusers out there that are perfectly smooth, or as near as is possible, but at $300 or so per copy. To what end? The mirror in my 10" f8 cost me $350 for figuring and coating, I don't think a $300 focuser is going to make it work any better. It has an off the shelf Boston rack, and the pinion cut from pinion wire. Works just fine, and a hell of a lot cheaper. Why complicate things? |
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On Tue, 30 Nov 2004 18:34:19 -0800, "Kelly Jones"
wrote: Off the deep end? Perhaps. But the original question was about how to check the rack and pinion, not whether it should be checked. I appreciate you pragmatisism, but it was still fun to describe how to do a pattern check. In all fairness to Kelly Jones, I did ask for how one would go about taking a fanatical approach to the wear on the rack and pinion. And I did find his reply interesting and informative, just as I found yours to be. I'm not really in a position to carry out his suggestions at the moment, and you're probably right that it isn't necessary, but I like to know how to do things, even if they're not appropriate to the task at hand, as long as I'm not under extreme time pressure to get something done (and with the weather the way it's been, there's nothing to look at in the scope anyway for the time being). Similarly, I realized that I probably don't need to buy a comparator, but it was good to learn about it, since I'd never heard of it. As long as there was one person who was telling me exactly how to handle the specific situation I was asking about, there was no real harm in getting supplementary information from others that was not immediately applicable. In the absence of that specific information, it would have been a different story, but I think I can tell the difference between what is immediately applicable and what isn't. If you don't mind, I'd like to ask about of your other comments, namely about the Taig lathe. I had never considered it and didn't know anything about it. I just took a look at http://www.taigtools.com and I see that the basic Micro Lathe II only costs $173 (or only $144, if I can assemble it myself, which I'm not sure I can do), and I think I saw somewhere that shipping is free if I buy it online. That's pretty tempting, but I may not realize that there is something else I would obviously need that would raise the price by a lot. I see that their milling machines are a lot more expensive. I learned about the Sherline by reading Joe Martin's book, Tabletop Machining. I see that the Taig website lists a book by Tony Jeffrey, entitled, "The TAIG Lathe". Would it be a good idea to purchase this book before committing to getting a Taig lathe? They show it with optional 3-jaw chuck, boring bar, tailstock, drill chuck, 1/4 HP 1725 RPM motor, motor mounting bracket, mounting board and pulleys for $399, presumably with free shipping for online purchase, which is less than the Unimat 1 comes to after taxes and shipping are added. Hmm, the motor is optional, as in no motor with the $144 deal? Of course, the Unimat 1 comes with the other stuff (notably the milling machine attachment), but one can't go too far wrong for $144, can one, as long as it works, and the other stuff can wait a little while. It's also probably easier to learn something by taking the Taig apart than a Unimat 1... I've decided on the first thing I will do when I finally get a lathe: I have a T-connector for my Minolta XG-1 camera (which, even with its apparently broken internal LEDs, is adequate for taking photographs through my microscope), and an adapter to connect it to my microscope. Now that I finally got my hands on a telescope, I tried to see if the adaptor would work with the telescope and, of course, it doesn't. But if I can machine a 1.25" O.D. tube to have a somewhat smaller O.D. near one end, I can use it as an adaptor adaptor, with the telescope eyepiece holder grabbing onto the 1.25" O.D. end and the camera-microscope adaptor grabbing onto the smaller end. This seems like the absolutely simplest first project one can do with a lathe, and I have an immediate use for it. The following is probably a bad idea, but it would be instructive to try out. I have a few eyepieces for my microscope. They are intended to fit the microscope barrel, but again it wouldn't be hard to make an adaptor that would let me insert them into the telescope. That is another very simple lathe project. Whether these eyepieces would be any good with the telescope is something I could then try out. Probably they wouldn't be, but I'd see for myself. The next problem would be to learn why, from the standpoint of optics, I should never have expected it to work in the first place. But there is a kind of information mismatch. The microscope eyepieces are only marked with their magnifications, such as 5X, 10X, 15X, while those for the telescope are marked with their focal lengths, such as 15mm,25mm,30mm. Even if the viewing isn't good, maybe I could wind up using the telescope to measure the focal lengths of the microscope eyepieces. In the absence of any optical equipment for doing such measurements, the idea of using a telescope as an optical lab bench is rather tempting, even if somewhat ridiculous. -- Ignorantly, Allan Adler * Disclaimer: I am a guest and *not* a member of the MIT CSAIL. My actions and * comments do not reflect in any way on MIT. Also, I am nowhere near Boston. |
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On 01 Dec 2004 03:49:43 -0500, Allan Adler
wrote: If you don't mind, I'd like to ask about of your other comments, namely about the Taig lathe. I had never considered it and didn't know anything about it. I just took a look at http://www.taigtools.com and I see that the basic Micro Lathe II only costs $173 (or only $144, if I can assemble it myself, which I'm not sure I can do), and I think I saw somewhere that shipping is free if I buy it online. That's pretty tempting, but I may not realize that there is something else I would obviously need that would raise the price by a lot. I see that their milling machines are a lot more expensive. The basic Taig is just that, the headstock, bed and carriage. Everything else is an extra, But it's still possible to have a complete lathe, with all accessories for under $500. IN the micro lathes, between one and the other, everything is different. The chuck for the Taig comes with soft jaws, which means, you have to learn to bore them. Not really a negative, but on the flip side, getting concentricity to where it's almost to little to measure is relatively easy. I learned about the Sherline by reading Joe Martin's book, Tabletop Machining. I see that the Taig website lists a book by Tony Jeffrey, entitled, "The TAIG Lathe". Would it be a good idea to purchase this book before committing to getting a Taig lathe? By all means. I haven't seen the book, but often a look at what someone else has done makes what you want to do much eaiser. Maybe Nick Carter will jump in here, he sells them and is very knowledgeable on what people are doing with them. They show it with optional 3-jaw chuck, boring bar, tailstock, drill chuck, 1/4 HP 1725 RPM motor, motor mounting bracket, mounting board and pulleys for $399, presumably with free shipping for online purchase, which is less than the Unimat 1 comes to after taxes and shipping are added. Hmm, the motor is optional, as in no motor with the $144 deal? Right. The package sounds very good, although I bought mine piecemeal, which probably cost me more in the end. The shortcomings of the machine show up, but by that time, you'll probably be far enough along to recognize them, and have an idea of what to do to clear them up. (There is no "perfect" machine for everythng.) One thing they don't push very much, the collets for it, this is something I bought quite some time after I had the basic machine and enough of the extras to make it work. They are invaluable when you have smaller diameter work, 5/16" is the biggest collet they have. Mine ran dead true and held like a bulldog. The instructions for assembling the kit sound somewhat simplistic, but that's really all that's involved, it only takes a few minutes, well, less than an hour. I've decided on the first thing I will do when I finally get a lathe: THis would be a very good project, not too much involved, but enough to learn from it. One of my buddies put a University mirror cell in an Oddesy scope, which moved the mirror forward almost 1 1/2", and no focuser has the reach to make up for that. Making an extention tube to move the eyepieces out was a relatively simple job, the Taig did well. The following is probably a bad idea, but it would be instructive to try out. I have a few eyepieces for my microscope. I've always had that idea, but have never acted on it. THe eyepieces are of a much different design from telescope EP's, and probably something is going to have to be done to compensate. IIRC, the focal plane of the microscope EP is between the lenses, but that's looking at older units. I have quite a few 10X and 15X wide field AO eyepieces, but as they're in scopes, I'm somewhat reluctant to risk taking them into the field. I spent hours going through a drawer of hundreds of eyepieces trying to match pairs, losing one of them would mean I couldn't find another to match it. I don't know any reason that they wouldn't work, and probably pretty well. |
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#35
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In article ,
Gunner wrote: On 30 Nov 2004 20:31:52 -0500, (DoN. Nichols) wrote: [ ... Micro-Vu optical comparator ... ] Out of curiosity, do you know which lens yours has? Not at the moment. Ill have to dig it out and look. I believe the magnification is 10x IRRC but which lens..no idea. It has the standard MicroVu screen and grid pattern. O.K. That screen has markings for three magnification ratios, 10X, 20X, and 40K IIRC. Mine has the 20X lens. (No real markings on it, you need to measure something of known dimensions to tell what you have. Frankly its in my way, and Id like to see someone get it. Ive a minty 12" Dorsey OC in my back office that I use and I understand that Ive just been bequeathed a Sony (? its orange) floor model with DRO. ("Its in my way..come and get it..we just got new CMMS and Mitys"...click) Well ... you are a bit too far away to make this practical, or I would be very tempted. :-) Thanks, DoN. -- Email: | Voice (all times): (703) 938-4564 (too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html --- Black Holes are where God is dividing by zero --- |
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e writes: The basic Taig is just that, the headstock, bed and carriage. Everything else is an extra, But it's still possible to have a complete lathe, with all accessories for under $500. IN the micro lathes, between one and the other, everything is different. The chuck for the Taig comes with soft jaws, which means, you have to learn to bore them. Not really a negative, but on the flip side, getting concentricity to where it's almost to little to measure is relatively easy. It makes sense that someone would purchase a complete lathe with all the accessories. If they already had accumulated some of those accessories from earlier acquisitions, it would make sense that they might forgo some of them when purchasing a Taig. It would then make sense that Taig might accomodate them by offering lathes without the accessories. But I'm not sure under what circumstances someone (other than a complete beginner like me, who doesn't know any better) might purchase a minimal $144 Taig that doesn't even have a motor. Is there a significant part of the market represented by people who already have a supply of motors? I spent hours going through a drawer of hundreds of eyepieces trying to match pairs, losing one of them would mean I couldn't find another to match it. I've been thinking about this statement and there are two things you might mean by it. (1) You sometimes take your eyepieces apart to scavenge the individual lenses to recombine them in ways you find more advantageous. I know from experience that they come apart, and I also found a website (e.g. http://www.astronomyboy.com/eyepieces) that tells you how to make your own telescope eyepieces, so this isn't unthinkable. It's another thing I was considering playing with when I get some machines. I'm not sure but it sounds a lot cheaper than buying eyepieces. (2) You have a binocular microscope and you need identical eyepieces for each eye. In the latter case, it sounds like you have all the eyepieces loose in the drawer but not grouped in matching pairs. If you had enough little boxes, you could group together all the ones that have the same magnification and not have to spend hours looking for matching pairs. Regarding the threads on the threaded metal shells that hold individual lenses in an eyepiece, are these threads that would be easy to duplicate with standard tap and die sets or is there something special about them? -- Ignorantly, Allan Adler * Disclaimer: I am a guest and *not* a member of the MIT CSAIL. My actions and * comments do not reflect in any way on MIT. Also, I am nowhere near Boston. |
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In article ,
Allan Adler wrote: writes: The basic Taig is just that, the headstock, bed and carriage. Everything else is an extra, But it's still possible to have a [ ... ] It makes sense that someone would purchase a complete lathe with all the accessories. If they already had accumulated some of those accessories [ ... ] Regarding the threads on the threaded metal shells that hold individual lenses in an eyepiece, are these threads that would be easy to duplicate with standard tap and die sets or is there something special about them? The only taps which are likely to be usable for that sort of thing would be the collapsable taps (sort of inside-out Geometric die heads) used on turret lathes or automatic screw machines. Optical threads of this sort are *very* fine relative to the diameter. The reason for this is because they typically screw into thin-walled cylinders, and fine threads are not as deep as coarse threads. And you wind up with really weird bybrid threads. IIRC (and I could well be wrong) the standard thread for microscope objectives is 0.800" x 0.5mm (Inch diameter and metric thread pitch). For production, you would use a collapsing tap to cut the inside threads, and a Geometric die head with custom chasers to cut the outside threads. For onesy-twosy work, you would single-point it on a lahte, which means (if you get a Taig) that you need to investigate Nick Carter's mod which gives it threading capability. Normal taps and dies are difficult to start square without some kind of machine support helping you. You *could* have any special tap and die made for you by the companies which make them, but it would cost you quite a bit, and you still have the problem of getting them started straight. And if you don't get them started straight, you have lens elements tilted relative to the axis of the equipment, thus offering optical abberations. I think that if you are going to be doing much of this sort of thing, you want to look for a dual-system lathe, with threading setups for both Imperial and metric threads. (To do this properly means two leadscrews with matching threading dials, and two quick-change gearboxes to provide the proper ratios for the different systems.) It is possible (with a set of transposing gears) to cut metric threads on an Imperial machine or vise versa, but it will be a serious pain, as you can't disengage the half-nuts until the thread is complete, with however many passes it requires. So -- while I have the Metric transposing gears for my Clausing, as long as the size can be handled by my little Compact-5/CNC, I will use it for metric threads, as all I need is to flip a switch to change systems. (And even then, the 0.800" x 0.5mm thread would require setting it up for metric threading, and converting the 0.800" to mm before programming the machine.) Enjoy, DoN. -- Email: | Voice (all times): (703) 938-4564 (too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html --- Black Holes are where God is dividing by zero --- |
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On 02 Dec 2004 22:55:28 -0500, Allan Adler
wrote: It would then make sense that Taig might accomodate them by offering lathes without the accessories. But I'm not sure under what circumstances someone (other than a complete beginner like me, who doesn't know any better) might purchase a minimal $144 Taig that doesn't even have a motor. Is there a significant part of the market represented by people who already have a supply of motors? Taig also sells the motors, but most people just use a scavenged motor from an old washer, dryer or whatever. 1/4 horse is plenty, I ran mine on 1/6 horse until I got tired of having to lift the whole thing, and the old motor was from 1937, HEAVY! Changed it over to a 1/12 horse scavenged from an old Bodine gear motor with the gear broken. If you can get a slower motor, maybe 1140 RPM, it would be better. Don't know if they're available on the surplus market or not. (2) You have a binocular microscope and you need identical eyepieces for each eye. In the latter case, it sounds like you have all the eyepieces loose in the drawer but not grouped in matching pairs. If you had enough little boxes, you could group together all the ones that have the same magnification and not have to spend hours looking for matching pairs. Bingo. Actually 5 binocs, two trinocs and a whole bunch of monocs. I like old things. Maybe too much. Matching them for power isn't too bad, but making sure they have the same aperture is where it gets fun, you have to hold the pair to your eyes, then swing the fields until they come together, they should be the same. (But usually aren't.) I don't have a good supply anymore, but used to work with J&H microscope on mods and accessories. You can get into some really wierd stuff. Regarding the threads on the threaded metal shells that hold individual lenses in an eyepiece, are these threads that would be easy to duplicate with standard tap and die sets or is there something special about them? Most of them that were made in the US had an unwritten standard of 40 threads per inch. Sometimes an odd ball of 36 TPI, but usually 40. Metric, I don't know about, I've been out of the attachment making for about ten years now, They're usually not included in the normal tap and die sets, but most of the supply houses will have them. The objectives, with only a very few exceptions, are .800"-36 TPI, 55 degree Whitworth threads. Most of the supply houses also have taps and dies for this as well. Prices are pretty reasonable. |
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On 3 Dec 2004 00:37:40 -0500, (DoN. Nichols) wrote:
snip For onesy-twosy work, you would single-point it on a lahte, which means (if you get a Taig) that you need to investigate Nick Carter's mod which gives it threading capability. Normal taps and dies are difficult to start square without some kind of machine support helping you. You *could* have any special tap and die made for you by the companies which make them, but it would cost you quite a bit, and you still have the problem of getting them started straight. And if you don't get them started straight, you have lens elements tilted relative to the axis of the equipment, thus offering optical abberations. I think that if you are going to be doing much of this sort of thing, you want to look for a dual-system lathe, with threading setups for both Imperial and metric threads. (To do this properly means two leadscrews with matching threading dials, and two quick-change gearboxes to provide the proper ratios for the different systems.) It is possible (with a set of transposing gears) to cut metric threads on an Imperial machine or vise versa, but it will be a serious pain, as you can't disengage the half-nuts until the thread is complete, with however many passes it requires. So -- while I have the Metric transposing gears for my Clausing, as long as the size can be handled by my little Compact-5/CNC, I will use it for metric threads, as all I need is to flip a switch to change systems. (And even then, the 0.800" x 0.5mm thread would require setting it up for metric threading, and converting the 0.800" to mm before programming the machine.) If I recall correctly, there was something called a Frog which could control a Taig, and would do threads under program control. Yeah, here it is http://www.avatartools.com/Merchant2/merchant.mvc I considered trying that, but wound up getting another lathe with threading capabilities before I ever pulled the trigger on purchasing a Frog. I kept the Taig, and still use it for a lot of little fiddly projects. It is excellent for small work. But threading jobs go on one of the other lathes, or get handled by taps and dies. Adding a Frog still looks like an attractive way to upgrade a Taig to 1 axis CNC. With 2 Frogs, you could do 2 axis CNC (the Frogs can talk to each other, so interpolated taper and radius turning would be possible in addition to fully automatic multipass threading). At $199 each, that's starting to cost real money, but it is still a lot cheaper than most CNC retrofits. Gary |
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