Thread Cutting

[Shuswap Pat]

I have a Harrison Lathe (domestic UK model), that doesn't have the right gearing combination to cut some North American thread pitches - (11 1/2 & 27 for pipe). I haven't had too much luck trying to find gears, at a reasonable price, so I was thinking of using a couple of #35 RC sprockets to give me the correct ratio when cutting these pitches. Any thoughts.

Pat

[kap pullen]

Pat,
Should work out fine.
Good thinking.
Harrison is a fine lathe.
The instrumunt company I worked for bought me one to use years ago.
kap

[Paul Alciatore]

Another thing you might consider is using gears of another DP in conjunction with your existing gears. You would have to have enough room on your mounting arm(s) to mount at least one compound in addition to present setups. The compound would consist of one of your present gears and one of the new DP. A second gear of the additional DP would mesh with the first and would be either on the stud, the screw, or on a second compound which would convert back to your original DP.

The additional gears would have to be mated with your existing gears to make the compounds. You can make or buy keyed bushings to combine two gears and/or they can be bolted together. I prefer bolting them as it does not introduce any additional backlash (lost motion if you are across the pond).

I don't know what gears you presently have but if you can cut 36 TPI then an extra pair with a 3/4 ratio should allow 27 TPI. And if you can presently cut 46 TPI then a pair with a 1/4 ratio should allow 11.5 to be cut.

Paul A.