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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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#1
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edge finder sensitivity
The recent thread on edge finders got me
wondering. I'm of the 'Spin it at 1000 or so, bring it slowly to the edge and watch for the "jump"" school. I have two edge finders, .500 and .200 diameter. All other things being equal, which is more accurate in finding an edge? The jump on the .200 is harder to see, but it almost seems more consistent. |
#2
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edge finder sensitivity
I like the 0.200 better. Just personal preference.
Karl |
#3
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edge finder sensitivity
On Aug 14, 1:55 pm, "BillM" wrote:
The recent thread on edge finders got me wondering. I'm of the 'Spin it at 1000 or so, bring it slowly to the edge and watch for the "jump"" school. I have two edge finders, .500 and .200 diameter. All other things being equal, which is more accurate in finding an edge? The jump on the .200 is harder to see, but it almost seems more consistent. I favor the .200" size but not for accuracy (which I have not compared between it and the .500) It's just easier, in my mind, to add .100" to the 'step off' dimension, rather than .250". Having said that, I used the .500" one for about 40 years before I even saw a .200" one. Lewis. ***** |
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edge finder sensitivity
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#5
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edge finder sensitivity
On Aug 14, 10:32 pm, "Terry Coombs" wrote:
wrote: On Aug 14, 1:55 pm, "BillM" wrote: The recent thread on edge finders got me wondering. I'm of the 'Spin it at 1000 or so, bring it slowly to the edge and watch for the "jump"" school. I have two edge finders, .500 and .200 diameter. All other things being equal, which is more accurate in finding an edge? The jump on the .200 is harder to see, but it almost seems more consistent. I favor the .200" size but not for accuracy (which I have not compared between it and the .500) It's just easier, in my mind, to add .100" to the 'step off' dimension, rather than .250". Having said that, I used the .500" one for about 40 years before I even saw a .200" one. Lewis. ***** The screws in my mill are 8 tpi . Easier for me to use the .500 , cuz it's zackly two turns of the wheel to center . -- Snag wannabe machinist I like the .200" dia. edge finder because my feed screws are .200" per turn and 1/2 turn gets me to the spindle center line :-)). Here is a question: Has somebody here actually TESTED an edgefinder to determine accuracy and repeatability? Never got to check it myself because the results were usually workable, but it would be nice to know. Wolfgang |
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edge finder sensitivity
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#7
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#8
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edge finder sensitivity
.... I have, but my results would not be helpful to others because particular edgefinders can vary quite a lot. A well-made edgefinder, e.g. Brown & Sharpe, is quite good. It gets even better if carefully lapped with fine compound, then carefully cleaned and lubricated for use. I trust my best edgefinder to half a thou, though I very rarely need that kind of accuracy. Another important factor is what you're mounting the finder in. We use a dedicated end mill holder and never remove the finder. Put the finder in a drill chuck and you haven't got much accuracy. I'm "kick school". My son proved to me that this puts the 0 point 1/2 thou too far over. "flick it and center school" is more accurate if you've got young eyes and a serious touch for machine accuracy. Karl |
#9
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edge finder sensitivity
On Aug 15, 1:15*am, Don Foreman wrote:
On Thu, 14 Aug 2008 19:43:47 -0700 (PDT), wrote:... Here is a question: *Has somebody here actually TESTED an edgefinder to determine accuracy and repeatability? ... Wolfgang ...I trust my best edgefinder to half a thou, though I very rarely *need that kind of accuracy. * I checked how repeatable mine was the other day because of this thread. It repeated to about half a thousandth turning at 600 RPM on a filed surface and I could get it within a thousandth by feeling for a step when it was stationary, which is how I use the center finder. When I want accuracy I surface-grind the block before milling and drilling. A surface-ground edge seems to behave differently with an edge finder, maybe it's the friction or lack of it? I haven't made anything recently that could be used to check the accuracy of the edge finder. Maybe a carefully bored hole near an edge would do. |
#10
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edge finder sensitivity
On Fri, 15 Aug 2008 03:11:49 -0700 (PDT), Jim Wilkins
wrote: On Aug 15, 1:15*am, Don Foreman wrote: On Thu, 14 Aug 2008 19:43:47 -0700 (PDT), wrote:... Here is a question: *Has somebody here actually TESTED an edgefinder to determine accuracy and repeatability? ... Wolfgang ...I trust my best edgefinder to half a thou, though I very rarely *need that kind of accuracy. * I checked how repeatable mine was the other day because of this thread. It repeated to about half a thousandth turning at 600 RPM on a filed surface and I could get it within a thousandth by feeling for a step when it was stationary, which is how I use the center finder. When I want accuracy I surface-grind the block before milling and drilling. A surface-ground edge seems to behave differently with an edge finder, maybe it's the friction or lack of it? I haven't made anything recently that could be used to check the accuracy of the edge finder. Maybe a carefully bored hole near an edge would do. ========= Anyone have accuracy numbers for the cheapscrew method of using a dowel pin and feeler gage or slip of paper? Unka' George [George McDuffee] ------------------------------------------- He that will not apply new remedies, must expect new evils: for Time is the greatest innovator: and if Time, of course, alter things to the worse, and wisdom and counsel shall not alter them to the better, what shall be the end? Francis Bacon (1561-1626), English philosopher, essayist, statesman. Essays, "Of Innovations" (1597-1625). |
#11
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edge finder sensitivity
On Aug 15, 1:25 pm, F. George McDuffee gmcduf...@mcduffee-
associates.us wrote: On Fri, 15 Aug 2008 03:11:49 -0700 (PDT), Jim Wilkins wrote: On Aug 15, 1:15 am, Don Foreman wrote: On Thu, 14 Aug 2008 19:43:47 -0700 (PDT), wrote:... Here is a question: Has somebody here actually TESTED an edgefinder to determine accuracy and repeatability? ... Wolfgang ...I trust my best edgefinder to half a thou, though I very rarely need that kind of accuracy. I checked how repeatable mine was the other day because of this thread. It repeated to about half a thousandth turning at 600 RPM on a filed surface and I could get it within a thousandth by feeling for a step when it was stationary, which is how I use the center finder. When I want accuracy I surface-grind the block before milling and drilling. A surface-ground edge seems to behave differently with an edge finder, maybe it's the friction or lack of it? I haven't made anything recently that could be used to check the accuracy of the edge finder. Maybe a carefully bored hole near an edge would do. ========= Anyone have accuracy numbers for the cheapscrew method of using a dowel pin and feeler gage or slip of paper? Unka' George [George McDuffee] ------------------------------------------- He that will not apply new remedies, must expect new evils: for Time is the greatest innovator: and if Time, of course, alter things to the worse, and wisdom and counsel shall not alter them to the better, what shall be the end? Francis Bacon (1561-1626), English philosopher, essayist, statesman. Essays, "Of Innovations" (1597-1625). Unka George, (we're probably a similar age?) I think that by using a dowel pin in a collet the accuracy of picking up an edge depends very much on the run-out(TIR)of the collet/pin combination. The kick-off type edge locator is much less affected by run-out. As others have mentioned the surface finish used to locate off is important; The better the surface finish the smaller the locating error, up to the point where the inherent process error governs. The point about lapping the two sliding surfaces on the locator is also a good idea. If one were really anal one would check the flatness of these surfaces with an optical flat and a monochromatic light :-)). As to whether the kick-off method or 'dead-nuts' concentricity gives better locating accuracy off an edge... I don't know for sure; but here is an observation based on physical principles: 1) Two objects cannot occupy the same space at the same time. 2) A 1" diameter pin will not fit into a 1" diameter hole without force. Based on this I would venture an opinion that the kick-off method is more accurate; it is certainly more precise ie. it has greater repeatability. ..0005" accuracy is, in all likelihood sufficient for most work. I run at 1000 RPM or so when edge finding, and also place a drop of oil on the pick-up edge to "improve" things :-)). Wolfgang |
#12
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edge finder sensitivity
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#13
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edge finder sensitivity
snippage
Another important factor is what you're mounting the finder in. We use a dedicated end mill holder and never remove the finder. Put the finder in a drill chuck and you haven't got much accuracy. more snippage Karl Actually, it doesn't matter how true the body of an edge finder is running as the action is only with the tip against the part that you are trying to locate. Try it...mount an edge finder in a drill chuck with a 1/32" shim under one jaw, then locate the same edge without the shim...same location. Mike |
#14
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edge finder sensitivity
F. George McDuffee wrote:
(...) ========= Anyone have accuracy numbers for the cheapscrew method of using a dowel pin and feeler gage or slip of paper? I dunno, but as a data point, teenut appears to say one can locate to within a tenth using oiled tissue paper and a mounted cutter. http://yarchive.net/metal/edge_finders.html See entry "Wed, 05 Jan 2000 23:07:11 GMT" --Winston |
#15
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edge finder sensitivity
On Aug 16, 3:12 am, Winston wrote:
F. George McDuffee wrote: (...) ========= Anyone have accuracy numbers for the cheapscrew method of using a dowel pin and feeler gage or slip of paper? I dunno, but as a data point, teenut appears to say one can locate to within a tenth using oiled tissue paper and a mounted cutter. http://yarchive.net/metal/edge_finders.html See entry "Wed, 05 Jan 2000 23:07:11 GMT" --Winston George, (I'll be 63 this fall) I read teenut's article you referred to; in fact I read the whole list. When you asked about the accuracy of the dowel pin-in-collet plus cigarette paper method of edge finding, and if you wanted to locate the spindle centre line over the edge, then my posting above is correct in that the collet/spindle/pin run out limits the accuracy of edge location. However, after reading teenut's old post it occurred to me that you may be talking about locating a work piece edge with the edge of a milling cutter. This is a horse of a different colour because here we want to determine the EFFECTIVE diameter of the cutter because the location of any edge machined, from the located edge, is determined by that EFFECTIVE cutter diameter which includes its wobble and run-out. The paper-stuck-on-work edge is very effective for this purpose. I have seen people use feeler gauge stock to do this but I wouldn't do that to a sharp cutter. Brass shim stock is what I have used for this purpose because its thickness is easily added to any dimension. With cigarette paper it is hard to tell how much to allow for; I suppose for most purposes the .001" thickness of the paper is ignored. Wolfgang |
#17
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edge finder sensitivity
F. George McDuffee wrote: FWIW - I use an electronic edge finder like this one. http://www.use-enco.com/CGI/INSRIT?P...PARTPG=INLMK32 Anyone have data on these? Unka George: This obviously isn't my normal sandbox, but in cruising through here this thread happened to catch my eye. Here are the relevant portions of a reply I made to an edge finder thread in amc. ================================================== ============= "Newsgroups: alt.machines.cnc From: BottleBob Date: Thu, 07 Apr 2005 01:48:38 GMT Subject: just how good are electronic edge finders? Paul: The solid stem electric edge finder is junk IMO. They run out even when new and all you have to do is overtravel a little too much and you tweak them. Electric edge finders are used with the spindle not turning. I also have a ball tip electric edge finder that I use from time to time but here too, you have to touch off your part, record the axis dimension then turn the edge finder 180 degrees and touch off again and subtract one dimension from the other and divide by 2 and move that amount to get the correct edge reading because they run out a little also. The thing about the ball type is it's spring loaded so if you overtravel a little you're not going to do it much damage. ================================================== ============= Also what has the groups experence been with the "audible" edge finder with a flat ground on the tip to produce a clicking noice? Less accurate? More accurate? than the standard edge finder? for examples see http://www.cartertools.com/fm.html#hfef (about 2/3s of way down) http://brownandsharpe.com/precision-...le-edge-finder I bought a couple of those "audible" edge finders that make a clicking noise when they "kick-out". They are not very loud in a noisy shop environment. They have a small flat ground on the edge finder. I tried them a few times but the spinning flat has a tendency to dig into soft materials, so I don't bother to use them anymore. The following bears on how the accuracy of an edge finder is influenced by the concentricity of the edge finder body. From an amc thread in 2003: ================================================== ================ Yesterday I made a $5.00 bet with another machinist, here is what it entails. Picture a 1/2" shank edge finder (.200 tip) in an ER 32 collet holder. Find the edge of a part to the nearest .0001, zero the axis. Take out the holder and put a narrow .010 brass shim between ONE side of the edge finder and the collet to simulate some severe runout. Re edge-find the same edge of the same part as before. Look to see how far off the axis reading is from before. I said it will probably be within .001 of the prior reading. We didn't have time to physically test this yesterday, but probably will Monday. Will I be $5.00 richer, or should I go try to dig up 500 pennies to pay off my gambling debt? g OK, here's what happened with the bet at work today. I took a 1/2" shank edge finder and put it in an ER-32 collet holder (made sure everything was clean with no mico chips that I could see), scaled the edge finder 1" from the top of the collet (I wanted to minimize any possible exaggeration if the collet taper or holder taper were off a little bit. Cleaned the spindle. Indicated a 1-2-3 block in the vise and cleaned out the spindle taper and installed the holder and edge finder. Called over my betting opponent and a witness that held the money, just a formality. Brought the Z axis down to -9.880 (recorded that figure so I could come to the same setting later), edge found the 1-2-3 block and zero'd the readout. Took the holder out of the machine and turned it 180 degrees to see if there was a difference, it was off about a .0001, no biggie. Took the tool holder out and went and made up a .015 think brass shim. The shim was about .400 wide and a little longer that the collet, I pre-bent it in a V-block with a transfer punch. Put the shim and the edge finder in the collet, not an easy fit, scaled the edge finder 1" from the collet. Tightened it up and went to the machine with my entourage. Brought the Z down to -9.880 and fed the edge finder over in ..010 increments, then .001 increments, then .0001 increments until it kicked out. It ended up being .0001 different than the original edge find. Much cheering, dancing, and commotion was seen and heard coming from MY corner! My betting buddy was pretty convinced but he wanted to try it in a drill chuck (just in case I had rigged the collet to tilt the precise amount the get my reading), we put the shim on one of the three chuck jaws, inserted the edge finder, tightened it, and went back to the machine. To make a long story short it was out .0002 from the original edge find. He was convinced, and took his loss gracefully. A fine time was had by one and all. LOL BTW, I plan to use my windfall profits to buy donuts for the shop tomorrow morning. ================================================== ================= -- BottleBob http://home.earthlink.net/~bottlbob |
#18
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edge finder sensitivity
On Sat, 16 Aug 2008 19:08:24 -0700, BottleBob
wrote: snip My betting buddy was pretty convinced but he wanted to try it in a drill chuck (just in case I had rigged the collet to tilt the precise amount the get my reading), we put the shim on one of the three chuck jaws, inserted the edge finder, tightened it, and went back to the machine. To make a long story short it was out .0002 from the original edge find. He was convinced, and took his loss gracefully. A fine time was had by one and all. LOL BTW, I plan to use my windfall profits to buy donuts for the shop tomorrow morning. ================================================= ================== Thanks for the insight and some real world experience and numbers -- much better than opinions. FWIW -- I have always had the spindle turning [c. 500 rpm] when using the electronic edge finder. Also very careful sneaking up to a contact. Light is not very bright though when it makes contact. Unka' George [George McDuffee] ------------------------------------------- He that will not apply new remedies, must expect new evils: for Time is the greatest innovator: and if Time, of course, alter things to the worse, and wisdom and counsel shall not alter them to the better, what shall be the end? Francis Bacon (1561-1626), English philosopher, essayist, statesman. Essays, "Of Innovations" (1597-1625). |
#19
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edge finder sensitivity
F. George McDuffee wrote: FWIW -- I have always had the spindle turning [c. 500 rpm] when using the electronic edge finder. Also very careful sneaking up to a contact. Light is not very bright though when it makes contact. Unka George: If the electric edge finder is spinning, AND if it runs out a little, it will probably light up when the high point contacts a conducting surface. But you really won't know if that high point is .0001", ..001", or even .010" off center. That's why I would contact your part with the edge finder stopped (then zero out your axis), back off your part, turn the edge finder 180 degrees and contact your part again to see if there is a difference in the two positions of the edge finder. Half that distance difference should be your off-center runout -- BottleBob http://home.earthlink.net/~bottlbob |
#20
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edge finder sensitivity
On Aug 17, 5:57 am, BottleBob wrote:
F. George McDuffee wrote: FWIW -- I have always had the spindle turning [c. 500 rpm] when using the electronic edge finder. Also very careful sneaking up to a contact. Light is not very bright though when it makes contact. Unka George: If the electric edge finder is spinning, AND if it runs out a little, it will probably light up when the high point contacts a conducting surface. But you really won't know if that high point is .0001", .001", or even .010" off center. That's why I would contact your part with the edge finder stopped (then zero out your axis), back off your part, turn the edge finder 180 degrees and contact your part again to see if there is a difference in the two positions of the edge finder. Half that distance difference should be your off-center runout -- BottleBobhttp://home.earthlink.net/~bottlbob I don't want to sound nit-picky about this but to be really certain about the effect of excentricity of the edge locator, the 180 degree turn-around test described above would need to be repeated at 90 degrees from the first tests. Unless, of course, you were really sure that at the first trial you indeed were at the high point of any excentricity. Wolfgang |
#21
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edge finder sensitivity
On Sun, 17 Aug 2008 02:57:14 -0700, BottleBob
wrote: F. George McDuffee wrote: FWIW -- I have always had the spindle turning [c. 500 rpm] when using the electronic edge finder. Also very careful sneaking up to a contact. Light is not very bright though when it makes contact. Unka George: If the electric edge finder is spinning, AND if it runs out a little, it will probably light up when the high point contacts a conducting surface. But you really won't know if that high point is .0001", .001", or even .010" off center. That's why I would contact your part with the edge finder stopped (then zero out your axis), back off your part, turn the edge finder 180 degrees and contact your part again to see if there is a difference in the two positions of the edge finder. Half that distance difference should be your off-center runout ========== Good observations, but as an old German tool maker told me years ago, after I took a drawing to him with 4 place decimals for some hole locations, if you can't measure it, it doesn't matter. I see several people have mentioned the Schmidt edge finders, https://www.hermannschmidt.com/produ...&idproduct=148 anyone have comments on /experience with the ones from Flexbar? http://67.59.156.7/merchant2/merchan...uct_Code=18509 Are these that much better than B&S or Starrett, or just more expensive? Unka' George [George McDuffee] ------------------------------------------- He that will not apply new remedies, must expect new evils: for Time is the greatest innovator: and if Time, of course, alter things to the worse, and wisdom and counsel shall not alter them to the better, what shall be the end? Francis Bacon (1561-1626), English philosopher, essayist, statesman. Essays, "Of Innovations" (1597-1625). |
#22
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edge finder sensitivity
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#23
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edge finder sensitivity
wrote: On Aug 17, 5:57 am, BottleBob wrote: If the electric edge finder is spinning, AND if it runs out a little, it will probably light up when the high point contacts a conducting surface. But you really won't know if that high point is .0001", .001", or even .010" off center. That's why I would contact your part with the edge finder stopped (then zero out your axis), back off your part, turn the edge finder 180 degrees and contact your part again to see if there is a difference in the two positions of the edge finder. Half that distance difference should be your off-center runout I don't want to sound nit-picky about this but to be really certain about the effect of excentricity of the edge locator, the 180 degree turn-around test described above would need to be repeated at 90 degrees from the first tests. Unless, of course, you were really sure that at the first trial you indeed were at the high point of any excentricity. Wolfgang: You wouldn't need to know, or be, on the maximum high point of any eccentricity to average out the runout in one axis. Let me try to explain it this way. Let's say the edge finder was bent toward the X+ side by +.001, so therefore the X- side would be bent away by -.001. Now when you touched the X+ side, (recorded your reading) then turned the edge finder 180 degrees and touched it again you'd have theoretically have a .002 difference. So half that difference would be roughly the center of the runout and spindle. Now the Y+ side of the edge finder could be +.005 and the Y- side could be -.005, BUT they don't necessarily influence the amount of runout in the X+ and X- sides. Was that clear as mud, or did it help? One thing that "could" influence the measurement of runout would be the the angle of the stem. If the very tip was touched on one side, and the other side was touched further up the stem due to being bent over... then the true runout would be skewed. Is this type of situation the ball tip electric edge finders would nullify any "bent tip" inaccuracies. -- BottleBob http://home.earthlink.net/~bottlbob |
#24
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edge finder sensitivity
F. George McDuffee wrote: On Sun, 17 Aug 2008 02:57:14 -0700, BottleBob wrote: If the electric edge finder is spinning, AND if it runs out a little, it will probably light up when the high point contacts a conducting surface. But you really won't know if that high point is .0001", .001", or even .010" off center. That's why I would contact your part with the edge finder stopped (then zero out your axis), back off your part, turn the edge finder 180 degrees and contact your part again to see if there is a difference in the two positions of the edge finder. Half that distance difference should be your off-center runout ========== Good observations, but as an old German tool maker told me years ago, after I took a drawing to him with 4 place decimals for some hole locations, if you can't measure it, it doesn't matter. Unka George: It might pay to indicate your electric edge finder from time to time, and tap it to get it centered if it runs out an appreciable amount. As far as the needed accuracy for your job, that depends on the job. Some can be scaled, some can be within a few thou, and some need to be within .0005. In the latter case I wouldn't count on the accuracy of electric edge finders, I'd either use a regular edge finder or indicator sweep your part and move over half the distance of your part. I see several people have mentioned the Schmidt edge finders, https://www.hermannschmidt.com/produ...&idproduct=148 anyone have comments on /experience with the ones from Flexbar? http://67.59.156.7/merchant2/merchan...uct_Code=18509 Are these that much better than B&S or Starrett, or just more expensive? I never felt the need to buy an edge finder more expensive than a good Starrett or B&S. So with the knowledge of me having no direct experience with Herman Schmidt or Flexbar edge finders... my OPINION would be that your money would be better spent in another area. IF you need better accuracy than a good Starrett edge finder can achieve (around ±.0005) then you need to consider using an indicator to find the edge of your part, either by "sweeping", direct indicating the edge, or using a "chair". http://www.wttool.com/product-exec/p...m_source=froog In using those you have to make sure the wall you're edge finding is perpendicular to your table or you might get an angular error. -- BottleBob http://home.earthlink.net/~bottlbob |
#25
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edge finder sensitivity
On Aug 17, 4:55 pm, BottleBob wrote:
F. George McDuffee wrote: On Sun, 17 Aug 2008 02:57:14 -0700, BottleBob wrote: If the electric edge finder is spinning, AND if it runs out a little, it will probably light up when the high point contacts a conducting surface. But you really won't know if that high point is .0001", .001", or even .010" off center. That's why I would contact your part with the edge finder stopped (then zero out your axis), back off your part, turn the edge finder 180 degrees and contact your part again to see if there is a difference in the two positions of the edge finder. Half that distance difference should be your off-center runout ========== Good observations, but as an old German tool maker told me years ago, after I took a drawing to him with 4 place decimals for some hole locations, if you can't measure it, it doesn't matter. Unka George: It might pay to indicate your electric edge finder from time to time, and tap it to get it centered if it runs out an appreciable amount. As far as the needed accuracy for your job, that depends on the job. Some can be scaled, some can be within a few thou, and some need to be within .0005. In the latter case I wouldn't count on the accuracy of electric edge finders, I'd either use a regular edge finder or indicator sweep your part and move over half the distance of your part. I see several people have mentioned the Schmidt edge finders, https://www.hermannschmidt.com/produ...sp?idcategory=.... anyone have comments on /experience with the ones from Flexbar? http://67.59.156.7/merchant2/merchan...uct_Code=18509 Are these that much better than B&S or Starrett, or just more expensive? I never felt the need to buy an edge finder more expensive than a good Starrett or B&S. So with the knowledge of me having no direct experience with Herman Schmidt or Flexbar edge finders... my OPINION would be that your money would be better spent in another area. IF you need better accuracy than a good Starrett edge finder can achieve (around ±.0005) then you need to consider using an indicator to find the edge of your part, either by "sweeping", direct indicating the edge, or using a "chair". http://www.wttool.com/product-exec/p..._medium=cpc&ut.... In using those you have to make sure the wall you're edge finding is perpendicular to your table or you might get an angular error. -- BottleBobhttp://home.earthlink.net/~bottlbob Bottlebob: Excuse the 'senior moment' on my part regarding the 90 degree babble. You are of course correct. As to geometric accuracy of the various features: Anyone who reads this ought to understand that attention to spindle squareness to the table, straight tool, work ref. surface finish and squareness is mandatory for accurate results. The latter is particularly important when using the 'chair gauge' you referenced. No sense in measuring the surface finish of a plowed field in micro-inches:-)). Jig borer operator in my training grounds used a gauge block held to the side of the work. First they swept the work edge and then the gauge block surface with the indicator. When the indicator needle stopped moving the spindle centre line was dead-nuts over the reference edge, say within .0001 or so. The beauty of this method is that no tooling errors are introduced into the process. Theoretically it may be used to achieve any accuracy required. Wolfgang |
#26
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edge finder sensitivity
wrote: On Aug 17, 4:55 pm, BottleBob wrote: IF you need better accuracy than a good Starrett edge finder can achieve (around ±.0005) then you need to consider using an indicator to find the edge of your part, either by "sweeping", direct indicating the edge, or using a "chair". Bottlebob: Excuse the 'senior moment' on my part regarding the 90 degree babble. You are of course correct. Wolfgang: Is that really your name? It's pretty cool if it is. Anyway, we all make the occasional conceptual boo-boo, it's no biggie. As to geometric accuracy of the various features: Anyone who reads this ought to understand that attention to spindle squareness to the table, straight tool, work ref. surface finish and squareness is mandatory for accurate results. The latter is particularly important when using the 'chair gauge' you referenced. Actually, I've got a magnetic "chair" and the "corner finder", but I seldom use them for the very reasons you mentioned above. Possible out of square issues. Jig borer operator in my training grounds used a gauge block held to the side of the work. First they swept the work edge and then the gauge block surface with the indicator. When the indicator needle stopped moving the spindle centre line was dead-nuts over the reference edge, say within .0001 or so. The beauty of this method is that no tooling errors are introduced into the process. Theoretically it may be used to achieve any accuracy required. Correct, and that particular method was what I was referring to when I mentioned "direct indicating the edge". And of course a "tenth" indicator is sometimes used when the tolerance requires it. Wolfgang -- BottleBob http://home.earthlink.net/~bottlbob |
#27
Posted to rec.crafts.metalworking
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edge finder sensitivity
I think you are a bit picky. That is what I was talking about.
The ionic isn't just liquids. If you have a molecule of Iron and in the mix is anything else (as in always) some part will be attached to Fe and the other part hanging out for something to bond to. Think of Carbon it can have Hydrogen attached or sulfur..... so a non-balanced molecule would be making an ionic bond to fill the requirements. Any part has error in the edge. The bar that is used to touch the sides has lots of errors in the 'so called' round bar. Might be an oval, a D or The flat of the 'chair' all sides have tolerances. Mixed with the 'bar' and this becomes a rich set of offsets. Mixed with a tilt of any kind or reason and it becomes richer in offsets with one or more angles causing a touch point to be different down the edge. In general the fast helpers are used when tolerance is tight. If you are making something for a shovel, than it wouldn't really matter. Martin Martin H. Eastburn @ home at Lions' Lair with our computer lionslair at consolidated dot net TSRA, Endowed; NRA LOH & Patron Member, Golden Eagle, Patriot's Medal. NRA Second Amendment Task Force Charter Founder IHMSA and NRA Metallic Silhouette maker & member. http://lufkinced.com/ BottleBob wrote: Martin H. Eastburn wrote: Precision measurements - maybe outside your area - are made with blocks. Martin: I think the term you're looking for is gage blocks, or Jo blocks (short for Johansson blocks). As far as "...maybe outside my area"; I probably have at least a passing familiarity in the use of Jo blocks as I've been wringing stacks of them together since my Tool & Die apprenticeship days in the early 70's. Currently, as an employee I have, and use, my own set of round Jo blocks plus use the shop's square set on a regular basis. The blocks are often in two or three materials and all hold by ionic or molecular forces. An example of an ionic bond is sodium chloride. The wringing, and adhesion of, Jo blocks is a phenomenon that has a number of possible hypotheses. Covalent bonding, metallic bonding, van der Waals force, Casimir effect, the expulsion of air between the surfaces and resulting 14 psi holding force, surface tension of water or oil, or a combination of any of the above or other factors not listed. So if there is a little coolant or sliver under an edge and a bur is within the corner relief - the coolant will hold off the edge providing some level of error. Then there are inherent errors on all edges including the touching edge of the finder. I'm not sure what the relevance of wringing Jo blocks is to putting a "chair" indicating device on the side of a part. But I'll certainly concede that burrs, slivers, and debris could throw off accuracy if they weren't cleaned off first. As I stated elsewhere in this thread, I don't often use the "chair" device due to it's, IMO, greater chance of introducing possible error. Often from tapered part edges. ----== Posted via Pronews.Com - Unlimited-Unrestricted-Secure Usenet News==---- http://www.pronews.com The #1 Newsgroup Service in the World! 100,000 Newsgroups ---= - Total Privacy via Encryption =--- |
#28
Posted to rec.crafts.metalworking
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edge finder sensitivity
On Thu, 14 Aug 2008 18:55:22 GMT, "BillM"
wrote: The recent thread on edge finders got me wondering. ============= Some URLs of interest about edge finders. First US patent appears to be in 1934 Some edge finder URLS of interest Cole et al in U.S. Pat. No. 1,984,864 http://www.google.com/patents/pdf/RE...OzWgMOKNVkSzSw Patent number: 2451904 Filing date: Jul 15, 1946 Issue date: Oct 1940 http://www.google.com/patents/pdf/LO...Py4iCLGES0v7Rw Moore chair Item # 3070-A Edgefinder, Inch $4,110.00 http://mooretool.thomasnet.com/item/...070-a?&seo=110 http://videos.findtarget.com/free_vi...dg/Using_Edge/ http://findarticles.com/p/articles/m...0/ai_n24384929 http://www.stanford.edu/group/prl/cg...le=Edgefinders Unka' George [George McDuffee] ------------------------------------------- He that will not apply new remedies, must expect new evils: for Time is the greatest innovator: and if Time, of course, alter things to the worse, and wisdom and counsel shall not alter them to the better, what shall be the end? Francis Bacon (1561-1626), English philosopher, essayist, statesman. Essays, "Of Innovations" (1597-1625). |
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