metric thread on my imperial lathe

That handle sounds like hard work

I am used to imperial threading on my imperial L5. I have the necessary gears for metric threading and understand what is necessary but what about the clutch? Should I leave it engaged all the time too?

I have no reversing switch on my motor so winding the carriage back is the issue. Will I be able to hand-wind the gears backwards with or without disengaging the back gear? Could I stop the motor and reverse the feed direction in order to use the motor for the rewind and still pick up the thread?

Any suggestion please!

If metric threading becomes a regular need I will fit a reversing switch at some point.

The mandrel handle may sound like hard work, but if that is the only way to do the job, you have no alternative.

Gives an incentive not to be too brave with depth of cut!

Do you have tumbler reverse on your machine? If YES, it can be used to ensure that the saddle moves AWAY from the Headstock while the chuck rotates in the normal direction, to produce the required L H thread..

BUT you do not touch it once you start cutting the thread! The relationship between spindle ( mandrel ) and leadscrew MUST remain the same until the thread cutting is finished.

My advice would be not to open the half nuts, but to withdraw the tool between cuts, and wind back the saddle by hand, if the motor cannot be reversed. Wind it back a little too far, to ensure that any backlash has been taken out before the tool starts cutting again.

Keep us posted!

Howard

morning folks, sorry for dragging up my old thread but i need to cut a 1.25 pitch thread now and ive lost the screwcutting book somewhere.

any help would be great, thanks

chris

Cut away from the shoulder and outwards from the bottom of a bore and these issues are non-issues.
From personal experience, and not from watching YouTube videos, it's easier not to open the half nuts when cutting Metric threads on an Imperial lathe

Chris, more info needed -- what make/model is your lathe, is it imperial or metric, or whats the lead screw pitch, what change wheels do you have etc.

John

Hi john, it’s all above but here it is my friend

harrison l2

imperial lathe

4tpi leadscrew

20, 40, 50, 55, 60, 60,80,127

First thought that comes to mind is:

If you have a note of the train for a 1.5 mm pitch, and it contains a 50T , (unless it is an Idler ) take it out and replace it with a 60T.

That should rotate the Leadscrew at 6/5 the speed of the 1.5 mm set up, and so produce a 1.25 mm pitch.

Howard

Edited By Howard Lewis on 29/02/2020 15:02:52

50/80/40/127

Edited - poor information.

Edited By Pete Rimmer on 29/02/2020 21:20:53

There are only 3 shafts for gears to go on, or do I double gears up on the middle?

I god a code in duh hed dis morning, so haven't checked the maths, but that's how I read Bazyle's instructions:

50 drives 80
80 and 40 on same shaft
40 drives 127

Although checking screw-cutting ratios on paper isn't rocket-science, I normally make a mess of it. Safer for me to set the gears up and check on the machine. Turn the lathe by hand to scratch a short spiral on a length of rod and measure the distance between turns in mm with a caliper. Or compare the scratched spiral with a known bolt or thread gauge.

Dave

If you go to this online calculator and put in "Other Lathes", your leadscrew and collection of gears, it gives you half a dozen alteratives including the one posted above . A handy resource to bookmark.https://littlemachineshop.com/reference/change_gears.php

Edited By Hopper on 01/03/2020 10:46:18

Edited By Hopper on 01/03/2020 10:48:55

Edited By Hopper on 01/03/2020 10:49:31