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View Full Version : 5/8X30 TPI (Lyman 310) Die


Antietamgw
06-07-2006, 10:14 AM
Anyone know how to cut 30 TPI in a lathe? My 9" South Bend won't, nor will a friend's 10" SB or Jet. I've not been able to find a 5/8X30 TPI threading die. I'd like to make a few special 310 dies for my use and hate to alter existing dies if I don't have to. Thanks for your thoughts!
grumpy one
06-07-2006, 07:28 PM
This depends on how your lathe works. 30 tpi is not listed on the chart for my lathe either, but it can be cut using a compound gear train - and there are too many possible combinations of these for them to be shown on the chart. I have a set of interchangeable gears, plus a quick-change gearbox in multiples of 2:1. To get 30 tpi I'd use a compound gear train made up from the change gears (30:40 and 50:20), which would give me 15 tpi, then run the quick-change in 2:1 mode. This would suit my 8 tpi leadscrew. If you have a 16 tpi leadscrew you'd have the quick-change in a 4:1 ratio.

I can't get more specific than this because lathes vary quite a bit, but 30 tpi does not sound like a difficult one provided you have a quick-change gearbox as well as change-gears in steps of 10 teeth, that can provide a compound gear train. Incidentally I've never cut a 30 tpi thread, but the above is what I get using the calculation formula that is on the gear-cutting chart for my lathe. I don't recall ever seeing a lathe with change-gears that can't be set up to create a compound train. I did have a problem once that the required combination of gears could not be installed due to incompatible diameters, and I overcame that by making up an additional idler pivot. Most things are possible, given some ingenuity.
Antietamgw
06-07-2006, 09:28 PM
"Most things are possible, given some ingenuity."

You're right, guess I wasn't thinking past what my Quick Change box told me. Thanks for the reply! The only change gears I have are those installed. I check and see if there is already a compatable combination with a little shifting around. If not, additional gears for South Bend are not that hard to find and maybe I can come up with something that will work.