Inserted cross slide feed nuts

You mention a load of crud in the recess; are you sure the insert wasn't pulled in rather than pressed.
i.e. a bit like a top hat bush, with the grub screw just to prevent subsequent rotation??

Maybe screw in the leadscrew itself, almost all the way, and tap the end with a suitable hammer and a bit of copper to protect the screw end.

Bill

Edited By peak4 on 24/06/2020 10:59:31

While heat cycling may loosen crud in the joint it requires cooling to loosen the insert - yellow metals have a considerably higher ceoff. of exp. than cast iron. I expect, if it were shrink fitted, it would likely drop out if immersed in liquid nitrogen.🙂

A simple puller made form bits would remove it.

After a good clean of the less accessible side of the insert in the saddle it seems that the hole behind the insert is 7/16 ( a good deal smaller than the front face of the insert) and there is no sign of a thread.

I decided that I was looking at a pressed nut and tried some cautious exploratory hitting on the end of my 7/16 brass bar. To my pleasant surprise it started to move before I chickened out.

So now it's out and pretty much undamaged I call that a result. Thank you for all of your input. Definitely a case of several heads being better than one.

The hole does indeed have a stepped recess.

I've miked the outside of the nut and (avoiding any potentially deformed areas) it reads between 5 and 10 thou over 0.5 inches... quite a wide range.

The compound will need a bit more thought because having cleaned out the crud it's clear that instead of a stepped hole the casting just overlaps part of the rear of the insert. I will need to make a custom punch to shift the nut but I'm not planning to mess with the compound until I've made some progress on the saddle. The saddle threads are pretty much trashed but the compound still has some life left in it.

For future reference I'd press the insert out or use the puller idea rather than hitting on the end of a brass bar but we will gloss over that for the time being.

Thanks again.

Good result, Andy

... it all seems obvious [albeit perhaps not very well made] now.

MichaelG.

Agreed. Pressing or pulling is definitely potentially far gentler than hammering.

Edited By not done it yet on 24/06/2020 15:25:30

Good result, now you have to decide what to do next, there is very little chance of finding a new one. If one is made, it would be safer to make it a just gentle push in fit and use Loctite, the cast iron is so thin on one side that there is a risk of cracking if the nut is tight.

Yes indeed... thoughts are turning to making a new nut.

Materials... I'm sure I've seen plenty of discussion on various forums, not all of them entirely relevant to an 80+ year old lathe. From memory the front running options seem to be brass (on the basis that it will wear in preference to the screw), leaded gunmetal or colphos 90.

Replacing the screw is also on the cards at some point. If I keep a square thread form then I can do one job at a time. If I was in the US then I'd probably buy some 3/8 x 12TPI LH ACME threaded rod and a matching tap all of which seem readily obtainable over there but not so easy/cost effective to get over here?

At the moment the plan is to use 3/8 silver steel to make a square thread profile tap (or is it three taps?) to match the existing feed screw. Then I can replace the feed screw as and when the mood takes me.

I will likely be doing this job several times over so making taps to suit should be worth the effort... if I can do it.

Hi Andy,

Great news Success now all the fun and work starts now

Good luck Brian

You might have some luck googling Kingston Engineering.

I checked HPC but theirs start at 0.5 inch. Kingston too. No doubt I could ask about a custom one but presumably that would be pricey.

Mc Master Carr does a 6ft length of 3/8 x 12 LH for 14 dollars in the US. HPC want 63 quids for a 1/2 inch one half as long in the UK.

I havent so far found any taps for a sensible price on this side of the pond either. Maybe there are some but I havent found them.

Locktite will make future removal difficult if the rapairer doesn't know it was used. You might consider boring out the rest of the length so the new nut can be longer - last longer. Maybe add a second screw to secure it.

I used a metric trapezoidal leadscrew and nuts on an imperial machine. The pitch is 3mm, that is close to 0.118", so a crosslide scale with 118 divisions was made for the lathe. The worn out original was 1/2 X8 ACME.

Tracey tools has ACME taps, rh and lh, but the 3/8 is 10tpi, and new leadscrews would be required. You will probably find that both nuts and matching threaded rod are the only way to go.

Yes I really want to stick with 12 TPI in spite of it being a bit silly.

The cross slide (the proper one, not the spare) has a nicely made brass resettable dial using the usual 80 graduation fudge. I'd be really loathe to lose that or make it so that the scale was meaningless.

How do you intend to produce a new nut in 3/8 x 12?

I think DiogenesII was correct yesterday. The hole is not concentric so the insert needs to be pressed into the casting and the hole and thread made in situ. So whatever thread I choose will need to be tapped I think.

Can I make a square thread tap (or three) myself?

No idea but I will give it a go. Worst case I will press the thing out again and go with a different option.

To find if the thread in the nut is concentric with the od, all you have to do is screw the nut on the leadscrew and see if it runs eccentrically. I would bet on it being in the same centreline, these big threads have a way of producing optical illusions. What is the OD of the nut?

Good point.

So I went and checked... but I think it really is not concentric.

OD measured at between 0.505 and 0.511 depending on where I measured it (and that was avoiding the ends and the area around the grub screw hole).

I assume that you took it off because it is so worn that the backlash is unacceptable. When the thread is worn, the wear may well be biased to one side, if there are sideways forces, or even gravity. I realise just from seeing the dreadful design (only an idiot would bore a casting so close to the edge) that you worry about the concentricity, but would it matter if the replacement was made properly?

Don't worry too much about my ranting about the quality, I have seen the guts of a Tom Senior mill, and the quality of that particular example leaves much to be desired in design and the dreadful casting quality.

Edited By old mart on 25/06/2020 20:33:57

Edited By old mart on 25/06/2020 20:34:28

Yes I was thinking that it might be worth just making a concentric one using single point threading... although even then I will need to make a tool to do a square thread inside a 7.4mm (I think) hole. The front plate on the cross slide is hardly high tech - just a flat steel plate with the hole for the feed screw and a couple of 1/4 BSW fixing screws. The 'aim' judging from the old nut seems to be about 0.5mm left of centre.

Whether an internal threading tool is a sensible idea is debatable. I've seen opinions expressed elsewhere that 3/8 is below the size at which one whould switch to tapping.

I agree the design is pretty odd. I don't think Faircut had really got the hang of the whole lathe thing when they made this but one can't be too critical - mine has lasted 80+ years and is still usable... plus they have provided me with a way to refurb the cross slide nuts - a job that would be a more difficult proposition on a lathe with the threads cut straight into the cast iron.

The nut in the spare is on the verge of a complete thread breakdown which is actually quite useful because I now have no qualms about messing with it. The proper one is not so bad but there is still significant backlash in my cross slide and if I can make it better then I would very much like to do so... after I use the spare for practice.