8 Acme 1 1/8 left hand internal

[restore49]

Inset options? repairing half nut - can I feed right to left back side of bore in reverse and use a 16er 8 acme insert -or will the tooth profile be wrong. Will make a new barrel and then cut away remains of threads and solder in .Bob

 

[Nick Hulme]

Not understanding exactly what you are asking?

 

[RM-MN]

If the thread is symmetrical it should work fine. Some may not be symmetrical.

 

[restore49]

Was thinking could make a new sleeve with internal 8 acme - then cut away remains of thread in original and solder in. Wanted to use insert to cut left hand internal threads in sleeve. Not sure I can use External right hand insert - can not find Internal Left Hand. Bob

 

[bmac2]

Hi Bob
You might try https://www.roton.com/ they have a good selection of left hand acme nuts and the prices aren’t too scary.

 

[restore49]

1 1/8 " 8 Acme not common - no learning curve in writing a check.

 

[mfrick]

When replacing the thread in the half nut you might run into a problem with the lead screw its self. On most lathes we use the section up close to the head stock the most. The most wear on lead screw will be on the head stock end of the screw which changes the pitch of the thread, so new threads in half nut will fit the tailstock end of the screw very well but will be lose on the worn portion.
Years back we use to take the half nuts out of the carriage and apron and machine the center section out and then set up on the tail stock end of the lead screw and pour Babbitt to replace the cast iron that we removed, it worked great made a great thread. :thumbup:

 

[Hopper]

I made a brass insert to go in my 8tpi halfnuts using a HSS bit in a boring bar. Ground the HSS bit to fit a standard acme gauge. Using an insert you just need to be aware the leading edge usually has more clearance than the trailing edge to allow for the helix of the thread. So a RH external insert should work ok for LH interrnal.

Usually the halfnuts will be softer material than the leadscrew so will wear out much faster. If the leadscrew is worn in the most used area, sometimes you can cut the threaded section off the leadscrew, turn it around and reattach with a spigot etc so the worn section ends up at the far right near the tailstock where it never gets used.

 

[restore49]

Thanks - Will be careful to check for clearance on insert - have ground HSS in past but eyes are not as young. - like the idea of factory ground insert. Was also thinking of using industrial epoxy to bond new sleeve to old block , not sure if this would be ok?? May try reversing lead screw idea if I find it worn beyond adjustment in the half nut. Can use the virgin end of leadscrew to test my fit of sleeve. This is a Cincinnati Tray top that sat unused in a friends cellar since 1974 in need of a gear Bob

 

[Hopper]

...Was also thinking of using industrial epoxy to bond new sleeve to old block , not sure if this would be ok?? ...

Should do. Specially if you make the insert bobbin shaped with a small flange on each end for location. Epoxy or solder, you will need to make sure the threads in both top and bottom nut are perfectly aligned, so it would probably be easiest to use epoxy and set the half nuts in position in the apron on the lathe and place the inserts in place with epoxy on them and then clamp the half nuts closed on the leadscrew to get perfect alignment and leave it for the glue to set. A bit of grease on the leadscrew might be an idea to keep stray expoxy from sticking, or a layer of cling wrap.

 

[restore49]

Bobbin shape is very possible - was planning to leave the sleeve intact until set and then cut in half. If I bore out the old threads accurately (make a jig to hold or use the apron) to match the OD of the new sleeve was thinking this would align ok??? Bob

 

[john_reese]

Several years ago I rebuilt the half nuts for a 20" lathe. The first step was to make a fixture to hold the half nuts in the lathe for boring and threading. I had the half nuts normalized to cook out any lubricant the iron had absorbed. I welded up the half nuts with oxy-acetylene using cast iron rod and borax flux. I had the half nuts normalized again for machinability. I bored them out and single pointed the threads. The tool I used was HSS that I ground myself.

It is absolutely essential that you get the half nuts fixtured properly before doing any welding. Design the fixture so the parts will return to their original position after they are removed for welding. The fixturing was the most complicated part of the job.

 

[Hopper]

Bobbin shape is very possible - was planning to leave the sleeve intact until set and then cut in half. If I bore out the old threads accurately (make a jig to hold or use the apron) to match the OD of the new sleeve was thinking this would align ok??? Bob

That's a good idea. It's the lateral alignment of the new threads relative to the old dovetails that is important too. I would do as you say, leave the new nut in one piece and split it after glueing to the bored out old nuts. To ensure both halves of the old nut are in the correct position when gluing in the new threaded insert, I would pop the old nuts into their dovetail track in the apron to keep them both aligned while the gluing the insert in.