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Thread rolling device

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madjackghengis:
Hi, I used to use thread rollers to thread spokes, both for bicycles, when I was young, and later, with six and eight gauge spokes for motorcycles.  As far as I know, all spokes are still roll threaded, as that is a substantially stronger thread, and it allows for an effective heavier gauge in the thread, while the spoke shaft remains light.  The thread rolling machines I used were hand cranked, with a set screw to tighten up one of the rollers, and they cranked right off, turning backwards.  I expect you would have no problem rolling those stainless spokes, and using the rolls you have on your lathe would entail making a holder with three angled axles, at least one set up for tightening, and I'd run the lathe at slow speed while pressing the tailstock by hand, up against the job in the chuck, once the rolls start, they will pull the tailstock if it's loose.  Definitely use lots of cutting oil, like knurling.  The stock should be approximately the final pitch diameter, but I think there is a section in Machinery's Handbook that gives a formula for figuring out the proper diameter.  Thread rolling is generally done on a screw machine, automatically, so tail stock mounting is generally the rule, as it allows fast retraction for the next screw.  For what it's worth, Mad Jack

ClydeBuilt:
Didnt know such a thing existed! I'll have to keep an eye out for that sort of thing.

Ideal for push rods etc in the rc model hobby, I tend to use pretty beefy ball/socket connections to save slop, a gadget like that would save a shedload of time looking out and setting up the die etc....lucky man!

Jasonb:
I think it is going to have to be a hefty fixture if you intend to use the M27 size, its hard enough using a ratched die stock to cut threads at that sort of size let alone squeezing the metal into place. A google for images of thread rolling machines will give a good idea of whats needed.

I don't see the need to release the rollers you could just reverse the lateh and back the work out unless you are intending to do a lot of long threads

Do the rolls have any form of lead on them to start the thread off as there are also hydralic ones which are pushed into the work and would probably not require any leadin.

Jason

madjackghengis:
Hi Jason, I know when thread rolling is used on a turret lathe, the third roller is the means for setting the final o.d., and the means for releasing the roller assembly from the finished thread, so it can be retracted straight back.  I did some work on a machine in a shop that made their own special screws for the machines they made, and I watched their turret lathe turn them out about one every fifteen or twenty seconds.  I think the lathe used hydraulics to lock the rolling assembly as it moved up to the blank, and released it as soon as the thread was complete so the turret could instantly retract.  You might have to use back gear to get the torque to turn the blank, but you can probably use them in a home lathe, that third wheel definitely needs a means of adjusting for thread depth and o.d.   :headbang: mad jack

Lew_Merrick_PE:

--- Quote from: madjackghengis on April 03, 2010, 12:27:11 PM ---The stock should be approximately the final pitch diameter, but I think there is a section in Machinery's Handbook that gives a formula for figuring out the proper diameter.
--- End quote ---

Mad Jack is generally (mostly sort-of kind-of) correct.  You are moving material from the "low side" of the thread to the "high side" of the thread.  As you squish material, it will reduce the total volume by a factor of 1 - 2*Poisson's Ratio for the material.  Rubber has a Poisson's Ratio of .50 -- which means that it stays the same volume no matter how you squish (or stretch) it.  Most steels have a Poisson's Ratio in the .270-.290 (.3 is the value taught in engineering classes) range.  Thus, if I have a block of steel that is a 1 unit cube and I squish it to .5 unit tall, I will end up with .5(1-2*.28) = .22 (i.e. 22%) less volume than I started out with.

Accounting for this in rolled threads is non-trivial.  It will depend on the exact metal and alloy with which you are working.  It is even somewhat dependent on the lubrication you are using.  As I recall (and this is from nearly 40 years ago which was the last time I rolled threads seriously), 4130 steel used a 7.5% increase over the pitch diameter for Unified National screw threads.

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