Hexagonal collet block in the mill vice will give you 6 positions or a square one rotating the work half an index would give you 8. For support use a machinists Jack under the overhang with a clamp on top of the work if you don't need to go all the way to the end. If you do you will have to move the clamp mid cut.

Why not bite the bullet and get a rotary table and tailstock though, once you have it you will find other uses for it.for parts for your engines.

Paul

Joe Pie's knurling lesson

You will need a lot more than a 2mm pitch thread, depending on the diameter and number of starts the pitch will be in the region of 1 to 2 times the diameter of the grip.

To do it you will need to workout the changewheels and to save straining the machine you turn the LEADSCREW by hand and that drives the spindle. Multi starts are best done with the topslide set along the lathe axis and if say using a 3 start thread then move the topslide 1/3rd of the pitch for each pass, 1/2 pitch for 2 start.

Edited By JasonB on 24/05/2021 07:10:37

This is what you want I presume.

This was an example for another thread from July 2018. Not easy on a lathe, you need a pitch equal to the circumference to get 45° helix angles. It is an example of helical milling which used to be done with a gear driven head mounted on a milling table but is now relatively easy to do with CNC if you have it.

On a lathe as you said driving the leadscrew would be best if you can set up suitable gearing, seems unlikely to me but you may find a way.

For a hand grip of about Ø25mm you would need a pitch of about 78.5mm. You then need to be able to index the part around by a suitable amount to get evenly spaced grooves. So let's say use 72mm pitch then you can divide this easily by 3 to give 24 positions around the circumference by just moving the carriage further along the leadscrew. Use similar sums if you have a machine with an inch leadscrew. This will be close to but not actually 45° but you could use a wooden dowel and marker pen to see if it works.

Martin C

I assumed a 3mm pitch leadscrew, hence the divide by 3 above.

Edited By Martin Connelly on 24/05/2021 18:13:47

You should just be able to reverse the leadscrew, I'm sure Myfords can do that so tool stays same way up but just cuts from the chuck to the tailstock for LH threads.

3mm pitch will still be way too little, compare the 3mm or 1/8" pitch of your leadscrew to the pitch you have drawn on the cardboard tubes to see how much longer the pitch needs to be. You just need to play with what change gears you have to get the longest pitch you can and try it with a sharpie in the toolpost like my video.