Myford type M half nut

Hi

i have recently acquired a myford type M in amazing condition. I’ve just stripped it down and cleaned off 80 years of grease embedded with brass filings and got to the half nut. This is novel to me as my previous lathe was the earlier drummond with a full nut. My question is what’s the top half for? The bottom half moves up and down on the bronze arm to disengage the lead screw but there’s a top half shell to the nut which doesn’t appear to be threaded. Is this just a support in case the lead screw bends under load?

Thanks

Dan

You have it right. The top half slides along on top of the leadscrew to prevent the leadscrew pushing away from the bottom half nut. It wears a little over time to have a impression of the leadscrew and that can give a ratchet effect as you traverse the saddle along. Just scrape and file it smoothe.

David

My mini lathe also has 1 half nut and is constructed the same as your myford lathe. On my mini lathe, There isn't enough space for a second half nut and a lead screw protection. Nevertheless, even with one half half nut, it serves me well over 10 years now.

There is a lot of good info on M-Types at the Drummond Lathes group here **LINK**

Check out the FILES section in the group homepage. Lots of good stuff there, including the essential how to adjust the rather unusual headstock bearings.

Check the condition of the thread in your lower half-nut. There is a repair procedure involving making a threaded "bobbin", cutting it in half and soldering it into a recess machined in the old half nut lever. It is a bit involved so unless the old one is completely stripped, not worth the bother. A bit of backlash there does not affect its operation at all.

Edited By Hopper on 15/03/2023 22:58:03

If you use your pal a lot you will burn through halfnuts, the bronze is very soft

I am looking at having some castings made. I have drawn and modelled the casting and looking at the pattern for casting in phosphor bronze.

David

PB may be too hard

I burned through 2 original leadscrew halfnuts in 12 months early in my ownership, it was a really soft type of bronze to save on leadscrew wear and maximise half nut wear

A small sample piece from your own one might be testable by someone who is familiar with these things

Edited By Ady1 on 16/03/2023 23:38:44

Hi David

So your making a new pattern.

Are going to have the boss cast whole so you can machine the full thread.

Should be possible to set up a jig on the faceplate to bore out and machine the thread in the casting.

Why not cast some in cast iron, easy to machine and the very early drummond nuts were c.i.

Geoff

The bronze casting will be half sided, the casting will be drilled and milled to give a datum and then it can be mounted on the crossslide on a jig with an inline boring bar, suported by the tailstock ccenter, with the thread form on to screw cut the thread moving in sidways per cut to depth of thread.

David

Edited By David George 1 on 17/03/2023 19:06:32

Edited By David George 1 on 17/03/2023 19:07:56

Thanks for the replies all.

It’s funny I’d been pondering what to do when the nut wears - try and cast another entire armature or just make a threaded section and solder or braze it on. For now it’s not an issue as it’s in very good condition and I’ve cleaned all the crud off and gone all 21st century with the lube. Dry ptfe spray and a very thin smear of moly grease with the intention of keeping it as immaculate as possible

regards

Dan

I made the traditional threaded "bobbin"-cut-in-half repair piece for my M-Type out of plain brass. It seems to have lasted well with no signs of wear yet. It was my only lathe for about five years used regularly for hobby work, including making my fabricated GHT versatile dividing head before I got the ML7 and shared the love around. So quite happy with the brass, plus it is supposed to be gentler on the leadscrew. Soft solder seems to have stood up well too, no doubt due to the shoulders at each end of the "bobbin" taking the load.

People turn their nose up at soft solder but those little solder on pipe repair patches you can get if you’ve ever drilled a hole in a heating pipe (guilty as charged), are pressure tested to 50bar

People turn their nose up at soft solder but those little solder on pipe repair patches you can get if you’ve ever drilled a hole in a heating pipe (guilty as charged), are pressure tested to 50bar

Hi Daniel,

This stuff is pretty strong as well, an old pre war cast iron arm with a bronze bobbin repair, still going strong after 10 years

Geoff