PM1236T: Are custom change gears available?

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macmccaskie

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The short of it, I'd like to cut ~1 TPI (bigger than 2 tpi) on a shaft, are different gears available?

The long of it. I'm working on a Quorn, one shaft has a spiral groove with the designer calling for 1 or 2 turns per inch. I'm not inclined to spend a grand on BS-2 dividing head and searching for alternatives. Any ideas, thanks.
 
So one turn ( revolution ) would move an inch ? Is this what you're asking ?
 
yep, 1/2 to 1 inch travel per turn with 1 inch preferred. with existing gears I can get 1/3 inch per turn.
 
Is it possible that a multi lead thread would work ? A 4 pitch thread with 4 leads as an example . :dunno:
 
One TPI is a hellova spiral. You would want the machine running dead slow for that one. Special gears. . . Naw. There is a train of gears between the reversing tumbler and input to the QCB. If you have one, even simpler if you don't. Simply cut down or speed up the gear train to provide a slower or faster speed before getting into the change gears. On my small machine, I was concentrating on getting a finer thread. Reversing that thought to get coarser is simply a matter of going the other way. But keep things dead slow, an inch per moves the slide fast. Rotating by hand is a common practice for very coarse threads on small machines. A crank or handwheel on the spindle. . .

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Is the purpose of the groove for lubrication?

You will most likely need to modify some off the shelf gears to work, an 18mm bore does not appear to be standard. To get to 1 TPI, you will probably have to change out the 120/127 gear as well to get the speed increase to turn the gearbox input shaft 4x what it was designed for. For metric gears, Mädler out of Germany has a good selection. This is their US operations https://maedlernorthamerica.com. The C45 gears are 1045 steel and would be fine for what you want, as well as easy enough to machine.

By time you buy all the gears needed, and tooling to modify them, it might be cheaper to farm it out to a local machine shop that can make the groove.
 
mmcmdl said:
Is it possible that a multi lead thread would work ? A 4 pitch thread with 4 leads as an example . :dunno:
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Unfortunately, no. The groove is for a height adjusting collar. Turn the collar adjusts the height of the grinding head.
 
macmccaskie said:
True, but I'm a stubborn cuss and have to do it myself :eek:. http://www.hemingwaykits.com could also send one to me for about the same cost.
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I like making things myself, but I’m not that stubborn, I would buy something suitable and spend my money on other things that could be reused. The gears needed to make this would probably only be used for this one purpose and never used again.

How often will that height need to be adjusted so much that you would need 1 TPI?
 
Got me wondering. On my lathe for 8TPI the top change gear is 25 T & the bottom one is 55 T. If I reverse those two I get 2 TPI. I gave it a try. Put a Sharpie in the boring bar holder and got 1/2" between marks. = two TPI.
Given the banjo on my lathe I don't have room to to put a 100 tooth gear on and the 25 T gear is about as small as can go on the bottom shaft.
At any rate if your selection of gears and allows a two time doubling from the set for 8 TPI or Even for 4 TPI, you should be in luck.
 
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