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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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Making a long threaded screw
Let's say I have a small lathe (length) and need to make a threaded screw
longer than the max length of my lathe. Obviously this can be done in theory by just threading one part, removing from the chuck, reinserting further back in the headstock and continuing the thread. But in practice can this be done with enough accuracy for something like a replacement lead screw for a lathe? Yes, I am aware of parts on Ebay and long threaded rods from MSC, etc. - this is more of a "how to use my lathe" machining question. Thanks. Steve. |
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SteveF wrote:
.. in practice can this be done with enough accuracy for something like a replacement lead screw for a lathe? No. |
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"Grant Erwin" wrote in message ... SteveF wrote: .. in practice can this be done with enough accuracy for something like a replacement lead screw for a lathe? No. Hey! Not true, at all! It's something of a chore to re-index a piece of threading work, but it's not that bad. Takes patience and time, that's all. Consider: Mark a thin scribe line down the length of the work to show the rotational indexing position. Position your tool in the thread very near the chuck, and lock the half-nuts. Then unchuck, and re-index the work in rotation by the scribe, and longitudinally by leaving a small amount of the already-threaded portion remaining beyond the chuck jaws, and using the (never moved) bit to find the correct longitudinal position in the chuck. Keep lost motion in mind, and snug the tool to the "cutting" face of the thread (by moving the work to the tool) before each re-chuck. LLoyd |
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You know, I don't think you can do it really accurately, but, if you
examine how a lead screw is used, you could probably do it well enough that it does not run into the boundary area often. Do it in 3 passes instead of two and you will probably never hit it, how often do you use the end 3 inches of thread on your lead screw? Lloyd E. Sponenburgh wrote: "Grant Erwin" wrote in message ... SteveF wrote: .. in practice can this be done with enough accuracy for something like a replacement lead screw for a lathe? No. Hey! Not true, at all! It's something of a chore to re-index a piece of threading work, but it's not that bad. Takes patience and time, that's all. Consider: Mark a thin scribe line down the length of the work to show the rotational indexing position. Position your tool in the thread very near the chuck, and lock the half-nuts. Then unchuck, and re-index the work in rotation by the scribe, and longitudinally by leaving a small amount of the already-threaded portion remaining beyond the chuck jaws, and using the (never moved) bit to find the correct longitudinal position in the chuck. Keep lost motion in mind, and snug the tool to the "cutting" face of the thread (by moving the work to the tool) before each re-chuck. LLoyd |
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In article , Grant Erwin says...
SteveF wrote: .. in practice can this be done with enough accuracy for something like a replacement lead screw for a lathe? No. LOL. The real long answer is, the task will be so time-consuming, and the outcome so uncertain, that you are better off doing it another way. Borrow a larger lathe. Purchase the lead screw and fit to your machine. etc. Short answer though is correct. Umm, not really. No. Also you did not specify any kind of lead accuracy tolerance on your requirement. A lot depends on that. If the tolerance is "it's gotta be the right number of tpi," then the answer could be yes. If you need ten microinch lead tolerance over the entire thing, then definitely no. The truth lies somewhere in between. Jim -- ================================================== please reply to: JRR(zero) at pkmfgvm4 (dot) vnet (dot) ibm (dot) com ================================================== |
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"SteveF" wrote in message
. com... Let's say I have a small lathe (length) and need to make a threaded screw longer than the max length of my lathe. Obviously this can be done in theory by just threading one part, removing from the chuck, reinserting further back in the headstock and continuing the thread. But in practice can this be done with enough accuracy for something like a replacement lead screw for a lathe? Yes, I am aware of parts on Ebay and long threaded rods from MSC, etc. - this is more of a "how to use my lathe" machining question. Steve, It's been about a quarter century since I've done this (CNC spoiled) but I'll give it my best shot. First off set your compound slide at 30 degrees and square up your tool and cut the first section of thread. In all likelihood your lathe has a threading dial on it and you engage the feed at the same number at every pass. If so, then what you need to do after you rechuck the part is to engage the feed on the same number, feed up close to a cut thread and shut the spindle off leaving the feed engaged. If your lathe doesn't have a brake be careful as the carriage will continue to feed as long as the spindle is rotating. Now use a combination of cross slide travel and compound slide travel to nest the tool into the previously cut thread. Note the numbers on your compound feed dial as they will be different than your first thread section. Depending on how fussy you want to be you can use an eye loupe or some Dykem, and rotate the spindle slightly by hand to make sure the tool is lined up perfectly with the previously cut section. Once you are satisfied that the tool is lined up with the thread, back the tool out, disengage the feed, back the carriage up, start the spindle and begin threading as normal by picking up the same number on the threading dial. HTH Dan |
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"SteveF" wrote in message . com... Let's say I have a small lathe (length) and need to make a threaded screw longer than the max length of my lathe. Obviously this can be done in theory by just threading one part, removing from the chuck, reinserting further back in the headstock and continuing the thread. But in practice can this be done with enough accuracy for something like a replacement lead screw for a lathe? Yes, I am aware of parts on Ebay and long threaded rods from MSC, etc. - this is more of a "how to use my lathe" machining question. Thanks. Steve. Given the proper setup, it's possible, but would be a serious challenge, especially if you are new at machining. You'd need a follow rest, possibly a steady rest, be able to feed the material through the headstock, and be able to pick up threads properly. Having considerable skill and experience would be the most valuable asset, along with soft jaws. Depending on how you pursued the project, you might be limited to length, but you could cut one longer than the center length of the machine. Harold |
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"Harold & Susan Vordos" wrote in message ... "SteveF" wrote in message . com... Let's say I have a small lathe (length) and need to make a threaded screw longer than the max length of my lathe. Obviously this can be done in theory by just threading one part, removing from the chuck, reinserting further back in the headstock and continuing the thread. But in practice can this be done with enough accuracy for something like a replacement lead screw for a lathe? Yes, I am aware of parts on Ebay and long threaded rods from MSC, etc. - this is more of a "how to use my lathe" machining question. Thanks. Steve. Given the proper setup, it's possible, but would be a serious challenge, especially if you are new at machining. You'd need a follow rest, possibly a steady rest, be able to feed the material through the headstock, and be able to pick up threads properly. Having considerable skill and experience would be the most valuable asset, along with soft jaws. Depending on how you pursued the project, you might be limited to length, but you could cut one longer than the center length of the machine. Harold I should have mentioned that the end product would likely be of questionable quality. Harold |
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In article ,
Harold & Susan Vordos wrote: "SteveF" wrote in message .com... Let's say I have a small lathe (length) and need to make a threaded screw longer than the max length of my lathe. Obviously this can be done in theory by just threading one part, removing from the chuck, reinserting further back in the headstock and continuing the thread. But in practice can this be done with enough accuracy for something like a replacement lead screw for a lathe? Yes, I am aware of parts on Ebay and long threaded rods from MSC, etc. - this is more of a "how to use my lathe" machining question. [ ... ] Given the proper setup, it's possible, but would be a serious challenge, especially if you are new at machining. You'd need a follow rest, possibly a steady rest, be able to feed the material through the headstock, and be able to pick up threads properly. Having considerable skill and experience would be the most valuable asset, along with soft jaws. Depending on how you pursued the project, you might be limited to length, but you could cut one longer than the center length of the machine. If I had a choice for this, I would probably use a Geometric Die Head to do it. Make the first cut as far as the turret would feed, then (after the head released), reposition the stock through the spindle, and close the Geometric on the existing thread, perhaps an inch or two from the end of the cut thread. Then switch spindle on again, and feed until end of turret travel again. If I were dealing with an Acme thread, or even a particularly coarse thread, I would use a Geometric Die Head with the rough/finish switch lever, and do two passes for each section. Actually, I've never seen Geometric chasers for Acme threads, but I could imagine them existing. 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 --- |
#10
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"DoN. Nichols" wrote in message ... In article , Harold & Susan Vordos wrote: "SteveF" wrote in message .com... Let's say I have a small lathe (length) and need to make a threaded screw longer than the max length of my lathe. Obviously this can be done in theory by just threading one part, removing from the chuck, reinserting further back in the headstock and continuing the thread. But in practice can this be done with enough accuracy for something like a replacement lead screw for a lathe? Yes, I am aware of parts on Ebay and long threaded rods from MSC, etc. - this is more of a "how to use my lathe" machining question. [ ... ] Given the proper setup, it's possible, but would be a serious challenge, especially if you are new at machining. You'd need a follow rest, possibly a steady rest, be able to feed the material through the headstock, and be able to pick up threads properly. Having considerable skill and experience would be the most valuable asset, along with soft jaws. Depending on how you pursued the project, you might be limited to length, but you could cut one longer than the center length of the machine. If I had a choice for this, I would probably use a Geometric Die Head to do it. Make the first cut as far as the turret would feed, then (after the head released), reposition the stock through the spindle, and close the Geometric on the existing thread, perhaps an inch or two from the end of the cut thread. Then switch spindle on again, and feed until end of turret travel again. If I were dealing with an Acme thread, or even a particularly coarse thread, I would use a Geometric Die Head with the rough/finish switch lever, and do two passes for each section. Actually, I've never seen Geometric chasers for Acme threads, but I could imagine them existing. Like you, I've never seen the inserts for Acme, but I can't help but think that using a die head for a thread of any length of substance would be a mistake, not that chasing it wouldn't present its own problems. If you're seen Acme taps, you know that they're considerably longer than a typical V type tap, so I'd assume the chasers for a die head would have to have a corresponding increase in length. Die heads were suspect enough when I worked at Sperry that they were not used. We single pointed all threads, some of which were really a tough job. One of them was a long manganese bronze shaft, 5/8" diameter, center distance, roughly 4" long, was cut 16 pitch, with the ends turned and ground for bearings, plus another thread or two. There were various configurations depending on the function. These went to the control system that fired the missile. I have and use a die head, but I've yet to see a thread that came from a die head that rivaled one that was single pointed, chased, although I have seen some quite pretty threads from die heads. Harold |
#11
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In article ,
Harold & Susan Vordos wrote: "DoN. Nichols" wrote in message ... [ ... ] If I had a choice for this, I would probably use a Geometric Die Head to do it. Make the first cut as far as the turret would feed, then (after the head released), reposition the stock through the spindle, and close the Geometric on the existing thread, perhaps an inch or two from the end of the cut thread. Then switch spindle on again, and feed until end of turret travel again. If I were dealing with an Acme thread, or even a particularly coarse thread, I would use a Geometric Die Head with the rough/finish switch lever, and do two passes for each section. Actually, I've never seen Geometric chasers for Acme threads, but I could imagine them existing. Like you, I've never seen the inserts for Acme, but I can't help but think that using a die head for a thread of any length of substance would be a mistake, not that chasing it wouldn't present its own problems. If you're seen Acme taps, you know that they're considerably longer than a typical V type tap, so I'd assume the chasers for a die head would have to have a corresponding increase in length. Agreed. I have (so far) *one* Acme tap, and would by preference single-point the thread in a single setup. But with the task stipulated -- cutting a thread longer than the travel of the carriage -- the requirement to pick up the previous part of the thread and continue with another section of the thread -- it strikes me that a die head would close nicely on the previously cut part of the thread to continue. As for the longer thread cutting requirement for Acme -- consider that Geometric chasers are available either plain, or with a projection to allow work closer to a shoulder, and that normally only the first few threads do the cutting, allowing many re-sharpenings. With a larger than normal Geometric head, it should be possible to pick up enough extra length so it would at least duplicate the extra length of the tap -- at the cost of many fewer resharpenings. Die heads were suspect enough when I worked at Sperry that they were not used. We single pointed all threads, some of which were really a tough job. One of them was a long manganese bronze shaft, 5/8" diameter, center distance, roughly 4" long, was cut 16 pitch, with the ends turned and ground for bearings, plus another thread or two. There were various configurations depending on the function. These went to the control system that fired the missile. I have and use a die head, but I've yet to see a thread that came from a die head that rivaled one that was single pointed, chased, although I have seen some quite pretty threads from die heads. One of the benefits of the die heads is that they can cut a full thread form -- and are intended to work from stock that is a few thousandths oversize, so you can mike over the crests to get a good idea whether they are oversized, undersized, or right on, without the need for the more expensive thread pitch diameter micrometer -- or juggling the thread wires and the tables or formulae to get the right measurement. It does make setup a bit easier at least. I normally use the Die heads when making batches of parts with the turret. The typical thread that I am cutting is 5/8-27 (microphone mount thread), and I am cutting it in 360 brass. Yes, I could single-point the thread, but in a situation like that (cutting to a shoulder, piece after piece for an afternoon and an evening), the Geometric die head is the better choice for me. (It is also a *lot* quicker than single pointing it, even with the rough/finish lever and two passes.) The other thread is a small metric -- for concertina endbox screws. M2.5x0.45 -- again done with the turret. A second lathe (A Taig, FWIW) is set up with a watchmaker's collet and a form tool to crown the heads, and then the Nichols horizontal mill with a fixture for holding twenty of them at a time in four rows for slitting with four slitting saws. Neither of these parts have a long enough engagement relative to the diameter for drift of thread pitch to be a problem, so I don't know how good that would be with the Geometric heads. But non-production threads I normally do single-point. 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 --- |
#12
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On Thu, 20 Jan 2005 05:16:33 GMT, SteveF wrote:
Let's say I have a small lathe (length) and need to make a threaded screw longer than the max length of my lathe. Obviously this can be done in theory by just threading one part, removing from the chuck, reinserting further back in the headstock and continuing the thread. But in practice can this be done with enough accuracy for something like a replacement lead screw for a lathe? Yes, I am aware of parts on Ebay and long threaded rods from MSC, etc. - this is more of a "how to use my lathe" machining question. Can you use the lathe to turn the stock, and use a die to cut your threads, or is this for a thread you don't have a die for? Novice question on my own part as well. |
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"Dave Hinz" wrote in message ... On Thu, 20 Jan 2005 05:16:33 GMT, SteveF wrote: Let's say I have a small lathe (length) and need to make a threaded screw longer than the max length of my lathe. Obviously this can be done in theory by just threading one part, removing from the chuck, reinserting further back in the headstock and continuing the thread. But in practice can this be done with enough accuracy for something like a replacement lead screw for a lathe? Yes, I am aware of parts on Ebay and long threaded rods from MSC, etc. - this is more of a "how to use my lathe" machining question. Can you use the lathe to turn the stock, and use a die to cut your threads, or is this for a thread you don't have a die for? Novice question on my own part as well. Well, that gives me two more questions for the group. One - Assuming some experience on the part of the operator in cutting threads and a good lathe, how much less accurate is using a die than cutting with the lathe? Two - How could one measure the thread to thread distance accurately to see how much error was created when reindexing after moving? Looks like thread micrometers only measure the diameter. Steve. |
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Two - How could one measure the thread to thread distance accurately to see how much error was created when reindexing after moving? Looks like thread micrometers only measure the diameter. Make a rig with two nuts, possibly (probably?) each made with some way of getting rid of play/backlash. Fix them so they don't rotate but allow some motion along the length of the screw. Start with them both on one side of your "join", measure the distance between (marks on) them, then move them so one is past the join and measure again. |
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On Thu, 20 Jan 2005 17:05:01 GMT, SteveF wrote:
"Dave Hinz" wrote in message ... Can you use the lathe to turn the stock, and use a die to cut your threads, or is this for a thread you don't have a die for? Novice question on my own part as well. Well, that gives me two more questions for the group. One - Assuming some experience on the part of the operator in cutting threads and a good lathe, how much less accurate is using a die than cutting with the lathe? It would depend on the quality of the die, compared to the accuracy of re-aligning the stock for the later cut(s). I'd like to think that a good die is going to give you the quality you'd need? Two - How could one measure the thread to thread distance accurately to see how much error was created when reindexing after moving? Looks like thread micrometers only measure the diameter. I'm interested in the answers you'll get to this. What kind of accuracy are you looking for? |
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"Dave Hinz" wrote in message ... On Thu, 20 Jan 2005 17:05:01 GMT, SteveF wrote: "Dave Hinz" wrote in message ... Can you use the lathe to turn the stock, and use a die to cut your threads, or is this for a thread you don't have a die for? Novice question on my own part as well. Well, that gives me two more questions for the group. One - Assuming some experience on the part of the operator in cutting threads and a good lathe, how much less accurate is using a die than cutting with the lathe? It would depend on the quality of the die, compared to the accuracy of re-aligning the stock for the later cut(s). I'd like to think that a good die is going to give you the quality you'd need? Two - How could one measure the thread to thread distance accurately to see how much error was created when reindexing after moving? Looks like thread micrometers only measure the diameter. I'm interested in the answers you'll get to this. What kind of accuracy are you looking for? If I can see or feel the break in the thread where the stock was moved, there really isn't any point in measuring it. A measurement would need to detect .01 or less. Steve. |
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| | It would depend on the quality of the die, compared to the accuracy | of re-aligning the stock for the later cut(s). I'd like to think | that a good die is going to give you the quality you'd need? Seems to me that if you used a die you would likely get good threads, but if you pulled or pushed on the stock while it was passing through the die you would gain or lose a thread or more over the length of the screw. Again, it's a tolerance stackup, but over a long item it adds up to be a whole bunch, especially on a lead screw. |
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On Fri, 21 Jan 2005 04:25:07 GMT, carl mciver wrote:
| | It would depend on the quality of the die, compared to the accuracy | of re-aligning the stock for the later cut(s). I'd like to think | that a good die is going to give you the quality you'd need? Seems to me that if you used a die you would likely get good threads, but if you pulled or pushed on the stock while it was passing through the die you would gain or lose a thread or more over the length of the screw. Again, it's a tolerance stackup, but over a long item it adds up to be a whole bunch, especially on a lead screw. Great information. Question though, is that an SAE "whole bunch", or a metric "whole bunch"? |
#19
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"SteveF" wrote in message
. com... "Dave Hinz" wrote in message ... On Thu, 20 Jan 2005 05:16:33 GMT, SteveF wrote: Let's say I have a small lathe (length) and need to make a threaded screw longer than the max length of my lathe. Obviously this can be done in theory by just threading one part, removing from the chuck, reinserting further back in the headstock and continuing the thread. But in practice can this be done with enough accuracy for something like a replacement lead screw for a lathe? Yes, I am aware of parts on Ebay and long threaded rods from MSC, etc. - this is more of a "how to use my lathe" machining question. Can you use the lathe to turn the stock, and use a die to cut your threads, or is this for a thread you don't have a die for? Novice question on my own part as well. Well, that gives me two more questions for the group. One - Assuming some experience on the part of the operator in cutting threads and a good lathe, how much less accurate is using a die than cutting with the lathe? Die cutting would not be very accurate for a long thread. The die will want to wander and the concentricity will be bad. I missed the part about cutting a lead screw in the OP. Precision lead screws are usually ground. Although some ball screws and lead screws today are cut out of hardened blanks on thread whirling machines. http://tinyurl.com/5bn5d Non precision lead screws (those not used in a machine tool) are for the most part thread rolled. Long threads like those on all-thread rod are through-feed rolled on a double roll type thread rolling machine. You can easily make a long machine screw to the accuracy required by cutting the threads in sections on a manual lathe. The problem with cutting a lead screw on a lathe is that all of the accumulated error in the lathes drive train, plus deflection, run out, slide wear, and thread form errors in your tool all stack up and prevent you from making a lead screw that's as good as the one in the lathe. Two - How could one measure the thread to thread distance accurately to see how much error was created when reindexing after moving? Looks like thread micrometers only measure the diameter. That is what the optical comparator was invented to do, check thread form and thread lead. http://www.qualitydigest.com/may02/html/optcomp.html Modern manufacturers of ball screws and precision lead screws use special electronic gaging machines that check the lead, run out, and accumulated error. Dan |
#20
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In article , Dave Hinz says...
Can you use the lathe to turn the stock, and use a die to cut your threads, A die won't give a precision lead to the part. Because this is a leadscrew for the lathe, that's not the best way to make the part. Leadscrews not only have to have the correct thread geometry, but they are effectively length standards in and of themselves. A die-cut leadscrew would work, but it would impart all the lead error into whatever parts were then fabricated when using it on the lathe. Jim -- ================================================== please reply to: JRR(zero) at pkmfgvm4 (dot) vnet (dot) ibm (dot) com ================================================== |
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On 20 Jan 2005 09:14:31 -0800, jim rozen wrote:
In article , Dave Hinz says... Can you use the lathe to turn the stock, and use a die to cut your threads, A die won't give a precision lead to the part. Because this is a leadscrew for the lathe, that's not the best way to make the part. Ah, I missed the part about it being a lead screw for a lathe. Leadscrews not only have to have the correct thread geometry, but they are effectively length standards in and of themselves. A die-cut leadscrew would work, but it would impart all the lead error into whatever parts were then fabricated when using it on the lathe. So...how does one cut a clean leadscrew when one doesn't have a clean leadscrew to start from? Someone made the first one... |
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In article , Dave Hinz says...
So...how does one cut a clean leadscrew when one doesn't have a clean leadscrew to start from? Someone made the first one... Screw threads have been fabricated for a long time, using manual methods like chasing. The real trick to to create the metrology needed to check them, and refine them. Basically you are talking jo blocks and maudsley. Jim -- ================================================== please reply to: JRR(zero) at pkmfgvm4 (dot) vnet (dot) ibm (dot) com ================================================== |
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"Dave Hinz" wrote in message ... On 20 Jan 2005 09:14:31 -0800, jim rozen wrote: In article , Dave Hinz says... Can you use the lathe to turn the stock, and use a die to cut your threads, A die won't give a precision lead to the part. Because this is a leadscrew for the lathe, that's not the best way to make the part. Ah, I missed the part about it being a lead screw for a lathe. Leadscrews not only have to have the correct thread geometry, but they are effectively length standards in and of themselves. A die-cut leadscrew would work, but it would impart all the lead error into whatever parts were then fabricated when using it on the lathe. So...how does one cut a clean leadscrew when one doesn't have a clean leadscrew to start from? Someone made the first one... I would guess (note the word "guess") that the better way would be to turn a couple of threads onto the end of the stock and then stick it into a precision nut which is the work holder for a grinding machine and grind the thread. The grinding wheel is always going to be a constant distance from the nut so just apply constant pressure to continuously turn the stock and work it into the nut and a screw of unlimited length could be done accurately. Maybe I can make an attachment for my lathe! Steve. |
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SteveF wrote:
this is more of a "how to use my lathe" machining question. I have absolutely no idea if this is going to work, but it is just an idea to save on 2nd, 3rd, etc, realignments (which probably saves nothing if you are making it for your own lathe). 1) Make first bit of threaded screw. 2) make threaded tube to match screw, tube extends through head stock, 3) make "lock nut" (or 2?) 4) mount threaded tube into jaws, 5) load lock nut onto thread part of screw 6) load threaded bit of screw into tube 7) lock threaded screw into threaded tube 8) align in jaws and tail stock 9) realign tool. 10) cut next section 11) unlock lock nut(s) 12) screw threaded rod through threaded tube and relock[1] 13) got to 10. Theorectically you could make it as long as you like, but you need steadies on the long bit, [1] each turn just advances the rod the size of the pitch. |
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