cutting a worm on the minilathe

I have a Cummins 7x12 minilathe and a nicely hand-ground Acme profile tool
I made. Right, so I have to cut a worm at 6.4 tpi. the change gears
with my 16 tpi leadscrew will be:
(30/50) x (40/60)
Can SKS tell me how to set this up so the gears actually mesh? Do I have
to somehow interpose an idler in there somewhere?
Help!
Mike in BC
Reply to
Michael Gray
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Mike, There are two adjustments. When you remove the cover, there is a nut lower than the change gears. Called an "adjuster" in this photo, (page 27 "Changing Gears") (PDF page 29)
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adjuster allows you to correctly set the engagement of the gears "A" and "B" There is a nut on the backside of the shaft holding gears "B" and "C", that nut will allow you to set the clearance of gears "C" and "D". Proper running clearance is one layer of thin paper. Set "C" and "D" first.
I don't see that gear combination or pitch. So, like cutting metric threads on any American leadscrew lathe, DON'T OPEN THE HALF NUT. You will lose sync, (and have a ~1/27 chance of finding it again.) You must stop the head, back the tool out, and reverse the rotation to move back to the start.
Good luck, Dave
Reply to
Mechanical Magic
Generally speaking you need to couple the 50 and the 40 together so they rotate in unison. Not sure how you do that on a mini lathe. A 24 and a 60 in the gear train give you the same ratio ( but I see from the grizzly web page that that the 7x12 does/may not have a 24 tooth gear).
Carl Boyd
Reply to
Carl Boyd
If the gears do not have keys to lock them together with, degrease them and stick a couple drops of superglue between them and press them together. It'll pop apart with some persuasion from a sharp edge driven between them, and acetone will clean the residue off.
Or you can just shoot a hole through them with a drill and tap it, and drop a screw through, if you don't want to trust the superglue to hold up.
If you have to resort to idlers, use 2. First idler will change the direction of feed, second to get it back into the direction it needs to go. If there is not a leadscrew reverse on the lathe.
Cheers Trevor Jones
Reply to
Trevor Jones
Thanks to all for the helpful comments. I've got it sorted now and found the following sites of help:
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I d/l NthreadsP.exe from lathes.co.uk and found it ran well by way of Wine on my linux (Ubuntu) box.
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explanation of what you're trying to accomplish with your change gears.
On some of these you can put in the data and a server programme will sort out the change gears for you (very handy), some let you d/l a programme so that you can "do it at home". I found that many of the programmes wouldn't run under Wine on linux, but they probably would be very comfortable under Windoze. Do check out NthreadP on the lathes.co.uk site, quite nifty I'd say.
HTH, Mike in BC
Reply to
Michael Gray

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