Metric thread on imperial lathe, without reverse.

[Ueee]

I'm not 100% on this, but other than Stuarts suggestion you can do it by reversing the leadscrew with the tumble reverse. You must however mark a tooth/valley on each gear and make sure you only engage the tumble reverse on the marks, for the cut anyway. Again, the half nuts must remain engaged the whole time.

I don't know why more lathes are not made with a single tooth reversing dog clutch like the hendys and some Holbrooks have. Solves the whole metric/imp threading issue.

Ew

[Oldneweng]

Thanks Fred ... I have an old Nuttall lathe, which has a leadscrew reverse lever already.

I just did a search on here and realised that I asked this very same question some time ago (2010) , but unfortunately I didn't post what the conclusion was. Although I seem to remember that I ended up opting for an imperial thread.

I might have to do some testing tonight and see what my options are in regard to the leadscrew reverse.

No can do (and I have tried) - the lathe has a clutch and it doesn't work correctly when run in reverse.

I cannot help with your question but I am interested in the fact that your Nuttall clutch doesn't work properly in reverse. Mine has a reversing motor on it and the clutch works fine regardless of direction. Maybe a different clutch or something.

Dean

ps My CY has that thing Ewan described. Harty69 explained it to me in relation to his lathe last weekend and I realised that my lathe had the same system.

I don't know why more lathes are not made with a single tooth reversing dog clutch like the hendys and some Holbrooks have. Solves the whole metric/imp threading issue.

[malb]

If you reverse the tumbler gears, you are effectively going to cut a left handed thread, it might or might not work by fully retracting the tool from the thread prior to running back with the tumbler reverse, then feeding back to the previous cut and adding the next cut before making the next pass.

The issue that will determine whether or not it works is whether you can change the tumber and have the gears engage repeatedly without needing to rotate the spindle or leadscrew even minutely. The few lathes I have dealt with (Southbend and Chinese) tended to have a tooth offset of about 1/5 to 1/3 tooth when operating the tumbler mechanism, meaning that the spindle needed a small tweak to engage the gears during the tumbler reverse operation. Remember that the tumbler mechanism is intended to select RH or LH thread before starting to cut the thread, rather than wind back the saddle in sync with the thread in the workpiece at the end of each cut.

My dad would have cut 1000's of threads with his SB in the 45 years he ran it, no chaser or dial gauge, always half nuts engaged continuously, cut lowest speed backgear or hand cranked, and returned by hand cranking at the chuck or faceplate.

[Michael G]

A while ago there was an article in MEW about this and the author made a threadng dial for metric threads on an imperial lathe. Because of the conversion between the two I think it had 127 teeth on it. This was because the first integer that converted inch to metric was 127.
For an occasional thread keep the half nuts in and reverse the spindle after winding out. Some people have made cranks or wheels that lock into the back of the spindle to make it easier to turn the spindle back.

Michael

[Vernonv]

I cannot help with your question but I am interested in the fact that your Nuttall clutch doesn't work properly in reverse. Mine has a reversing motor on it and the clutch works fine regardless of direction. Maybe a different clutch or something.

Hi Dean. I did the test in 2010 and I found (if I remember right) that the clutch permanently engaged when I ran it in reverse. My Nuttall is a 1948, threaded nose model.

I didn't get a chance to do any testing last night, although I did get it mostly setup. Hopefully tonight I will have a go at it.

[PDW]

ps My CY has that thing Ewan described. Harty69 explained it to me in relation to his lathe last weekend and I realised that my lathe had the same system.

It solves more than the metric threading issue. You can screw-cut at higher speeds without risking a crash or needing lightning reflexes and you can use it under power feed to a shoulder and walk away to do something else without a worry about getting back before a crash. I use it all the time on my Monarch CY.

PDW

[Oldneweng]

Hi Dean. I did the test in 2010 and I found (if I remember right) that the clutch permanently engaged when I ran it in reverse. My Nuttall is a 1948, threaded nose model.

I didn't get a chance to do any testing last night, although I did get it mostly setup. Hopefully tonight I will have a go at it.

Mine is about the same period and chuck mounting is also screw on, as in threaded spindle. My lathe has a combo clutch and brake although the brake has stopped working. Needs adjusting I think. I had forgotten it even existed until I started to think about how the clutch operates. If the handle is not engaged the brake should be automatically applied. The brake consists of a friction disk that presses against the outer end of the clutch housing which has a raised disk for this purpose. Is this similar to yours?

IMG_0651.jpg

I have found a picture of yours and although it looks more pretty it is the same.

Dean

[Retromilling]

If you have the correct gear combination for the pitch then it is possible to disengage the half nuts without using a thread dial . You have to close the half nuts and pull the lathe forward to start near the thread start . Then put three witness marks on the lathe. One on the backing plate to head stock. One on the lead screw to gearbox housing and one on the bed way at the edge of the carriage .
Start the lathe and take the first cut and disengage as normal . Then move the carriage back to that mark , pull the lathe around until the other two marks line up if you miss go back and pull forward again to stop backlash , move the carriage in towards the chuck to line up and close the half nuts and you should be back in the same starting point. Increase the cut and start the lathe . That's as best I can remember I have never done it myself but I have seen it done by a person I knew years ago and on a you tube video a while back which I will try to find again .
I think this is the same one https://www.youtube.com/watch?v=FNajMA4I20A

[cba_melbourne]

It's been a long time since I cut a metric thread and I can't remember if I have even cut one on my current lathe (which doesn't have a reverse).

Anyway, my question is .... is it possible to cut a metric thread on an imperial lathe, if I disengage the half nuts and reposition the tool at the same location and start on the same number on the thread dial, for each pass?

Vernonv, the answer to your question is an unconditional no. And I am 100% confident about this.


If your lathe had a metric leadscrew, then you could open and close the halfnuts wherever you want and how often as you like and without using a thread dial, for those metric thread pitches that are contained as a whole number in your leadscrew pitch. For all other metric pitches you could use a thread dial if available. But since your lathe is imperial (eg has an imperial leadscrew), there is absolutely NO way to disengage the half nuts without ruining the thread being cut. Some people may claim you can with some tricks, but your chances of getting onto a "false match" are many times greater than hitting by chance the one and only engagement point that exists. Without a reverse on the spindle, your only option is as suggested earlier, leave the halfnuts closed and turn the spindle backwards by hand. Chris

[Vernonv]

Is this similar to yours?

Yes, as you said, it's the same ... although I didn't realise it braked as well - I guess that doesn't work on mine either.

So your clutch works regardless of the direction of rotation?
Maybe I need to have a closer look at the clutch mechanism.

You don't happen to have a manual do you?

[Oldneweng]

Yes, as you said, it's the same ... although I didn't realise it braked as well - I guess that doesn't work on mine either.

So your clutch works regardless of the direction of rotation?
Maybe I need to have a closer look at the clutch mechanism.

You don't happen to have a manual do you?

Unfortunately I don't have a manual. Just had a quick look again on the net. I had a look when I first got it but had no success. I found a reference on PM from 2008, to a very worn Nuttall purchased by "RC99" whose location was given as "near Rockhampton, Queensland, Australia". Also a thread on this forum from 2009 with discussion from .RC. and an "Old Croc" who it appears was about to receive a manual. Title "Nuttall Lathe Manual".

I also found this picture of a very well preserved unit.

Nuttall Lathe.jpg

This was on Lathes.co.uk. They don't have a manual.

I cannot help much but if you need pictures just let me know. They may be of some use. I broke the clutch housing by dropping the lathe when moving it into my shed and had to weld up a replacement. The clutch/brake mechanism is self supported on the shaft so the only thing the housing did was to provide a fixed surface to brake against and a cover over the top. This cover survived.

Dean

[Retromilling]

I'm not 100% on this, but other than Stuarts suggestion you can do it by reversing the leadscrew with the tumble reverse. You must however mark a tooth/valley on each gear and make sure you only engage the tumble reverse on the marks, for the cut anyway. Again, the half nuts must remain engaged the whole time.

I don't know why more lathes are not made with a single tooth reversing dog clutch like the hendys and some Holbrooks have. Solves the whole metric/imp threading issue.

Ew

It's not such an issue on a modern lathe with an instant stop foot brake . I cut metric and Imperial on an Imperial lead screw and never use a thread dial on Imperial . I just hit the foot brake and the lathe stops dead on , back out and reverse . On an instant reverse three phase lathe you can just whack the lever into reverse as you back out or use the brake . Not having reverse would be a bitch .

[Vernonv]

Ok I cut the thread. A few things to note:

1. My lathe has a brake . Works really well at lower speeds (stops it dead) and slows the chuck much quicker than normal, at high speeds.

2. Reverse lever (for the carriage only) does not bring you back to the correct spot when metric threading.

3. I had to reverse the chuck by hand, with everything engaged to get back to the start of the thread. Of note was that I could change the gearbox from slow to fast to allow me to easily reverse the chuck and it reversed to the correct start position. I could then change back to slow to cut the thread.

4. I needed to cut an M16 x 1.5 thread (16.9333 TPI) and using the standard change gears (only 3 of them ), I could get (using the Lathe Gears program to work it out) to 1.511mm (16.8 TPI) which is a 0.79365% error. That was close enough for my application.

Only thing left now is to revisit the clutch operation when the motor runs in reverse - it's a 3 phase motor so will be easy.

[Oldneweng]

Ok I cut the thread. A few things to note:

1. My lathe has a brake . Works really well at lower speeds (stops it dead) and slows the chuck much quicker than normal, at high speeds.

2. Reverse lever (for the carriage only) does not bring you back to the correct spot when metric threading.

3. I had to reverse the chuck by hand, with everything engaged to get back to the start of the thread. Of note was that I could change the gearbox from slow to fast to allow me to easily reverse the chuck and it reversed to the correct start position. I could then change back to slow to cut the thread.

4. I needed to cut an M16 x 1.5 thread (16.9333 TPI) and using the standard change gears (only 3 of them ), I could get (using the Lathe Gears program to work it out) to 1.511mm (16.8 TPI) which is a 0.79365% error. That was close enough for my application.

Only thing left now is to revisit the clutch operation when the motor runs in reverse - it's a 3 phase motor so will be easy.

I guess that you don't have the metric thread cutting gears for your lathe. They came with mine. I am going to have another look at my clutch/brake setup and take some pics. I would like to fix the brake but as the lathe is not really mine anymore I don't plan on spending much time or money. Might be a good idea to have some photos for when it is gone. Wont be far away tho.

Dean

[Stustoys]

Vernonv, the answer to your question is an unconditional no. And I am 100% confident about this.

100% is a lot.

I think I've just done the maths on cutting a 1.5mm pitch on an 8 tpi leadscrew.
Now if I'm right you get exact pick up every 127 pitches(60 turns on the leadscrew). Only 22 of the other turns will the leadscrew be within 36 degrees of TDC with the chuck is at TDC. So granted....... it could be tricky on the fly and at 75rpm... slow.

But this idea might work.
Make up a gage that allows you to move the carriage 7.5" +/-1/32(you just need to be on the correct "turn" of the leadscrew"
Cut your thread, turn the lathe off, open half nuts, move the carriage back 7.5" close halfnuts, cut thread, repeat.

I cant check my maths on the lathe as its metric.

IF the above idea works, another idea you could make up a thread chaser dial with a 60 tooth* gear, wouldn't that let you pick up on the fly?

Granted this wont exactly be fast as you'll effectively be cutting a 7.5" long thread regardless of how much you want.(though you do get quick return unlike full reversal, if the chaser works you wouldn't even be turning the lathe off)

Stuart

p.s. Surely I'm missing something?

0.5 pitch = 2.5" reset
0.25 pitch= 1.25" reset

0.5 pitch = 20 tooth gear
0.25 pitch = 10 tooth gear

p.p.s I've got to be missing something!