Advice needed - double start worm thread

[morrisman]

Hi

More model train dilemmas !

These brass worm gears are for the venerable Triang X04 motors , they are made from unobtanium .

So how does one go about machining a 2 start thread such as this ?

thanks

Mike

[Stustoys]

Well that depends on the thread and your lathe.
If the thread is the same type as the leadscrew on your lathe and the pitch isnt one that can be dropped in anywhere, you can just use the thread chaser to pick up 180degrees out.
Other than that I dont know how you do it.

Stuart

[Michael G]

Another way is to cut the first thread and then advance the compound half the lead to cut the second - this will only work if you keep the compound parallel.

The second way that may work for you that I can think of is to mark the relation of two of the gears in the train between the spindle and the leadscrew, remove one, rotate the spindle 180 degrees and then replace the gear. This should make it 180 degrees out of phase.

Michael

[morrisman]

OK thanks for the suggestions , I see it's relatively simple .

I just measured the thing.... the outer diam. is .250" . And, measuring the pitch of each 2nd thread , it is .100" , so that means .050" between each thread. So the single pitch of each thread is .100"

I think I can do it, I just need to grind up a tool and find some 1/4" brass stock and set up the lathe to cut a .1" pitch ( 10 tpi ) thread .

Mike

[Metalman]

If you have a Camloc chuck with the right number of pins you can index the chuck and just cut the same thread again.
Mm.