So if I had an inch leadscrew I could just use a 127 tooth gear and work out the ratio and get a metric thread; is there a gear-based way to reverse this?
Lathe in a 7x10; tpi I need is 56 - closest it'll do with standard change-geas is about 56.44 - not good enough for the length of thread that will be in the spoke nipple.
(no I'm not cutting spoke threads on a lathe, I'm making new rollers for the thread roller 'cause the old ones are badly worn)
Sure -- for one style of conversion, the input is to a 100 tooth gear, and the output from the 127 tooth gear (keyed to rotate together on a common shaft). For the other style of lathe and conversion, the input is to the 127 tooth gear, and the output from the 100 tooth gear.
In either case, note that the threading dial will be useless (though a bit of fudging can make it work, sort of). Normally, you have to leave the half-nuts engaged, and reverse the lathe to get back to the start of the cut.
Hmm ... I seem to remember reading that there is no threading dial (and no half nuts) on the 7x10 machines. Am I wrong on that?
Hmm ... what is the thread form on those? A standard 60 degree included angle? 55 degrees (Whitworth), or something else entirely. If anything but 60 degrees, you will have to grind your own threading tool, as the standard insert tooling is only 60 degrees (at least, what I have found in the USA).
Good Luck, DoN.
No, you are correct - it means I turn it off, pull the tool out, and reverse the motor.
Tool bit's already ground, 60 degree, the radius of the inserts I have was too big anyway. If it ain't supposed to be 60 degrees, well at that small a thread there won't be much difference.
O.K. A real pain -- but not much more than normal threading on the same machine, other than the having to build up a special geartrain.
[ ... ]Hmm ... the screws holding the endboxes on older English-system concertinas (say from around 1850 or so) are strange beasties. Diameter is 0.100 (roughly), and the threads are very coarse for the diameter, 42 TPI, IIRC. As a result, the threads are rounded root and crest, and about 90 degrees included angle. (60 degrees would have resulted in the root being somewhere near the center of the shank, so it would have been more like a corkscrew. :-)
I wonder how they cut that coarse a thread in that small a diameter of bronze back then?
Good Luck, DoN.
Rather than going on a quest for gears you may or may not find, why not get the real deal, an inch leadscrew and halfnuts?
Stan
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