Inserted cross slide feed nuts

I'm not sure if Faircut used a design similar to other lathes but so far my searching hasn't turned up anything similar. The nut is a non ferrous insert into the saddle (the compound and tailstock barrel have a similar arrangement).

A slotted grub screw bears on the insert. I've got the screw out (it broke a bit) but I'm not much wiser. A straight pull with the leadscrew showed no sign of shifting it. The lack of concentricity on the cross slide insert suggests it may be threaded but getting anything to turn it will take some thinking. The compound insert doesn't show such noticeable eccentricity.

I can speculate on how to shift it (or drill it out) but I'm hoping that someone has seen something similar and can give me some clues.

At a guess, it is merely pressed in. You should measure both ends just in case there is a shoulder, otherwise some sort of puller should be made, or use a press if you have one. If you are still concerned about the possibility of it being screwed in, then either turn up a piece of metal that just fits the bore nicely, with an end the same size as the interface between the bronze and cast iron. That would prove the presence or absence of a thread. You could also measure the interface diameter at several angles to see if it is round or not.

The other end is quite deeply recessed in the casting so it's not possible to do any useful measurements there (same on the compound).

The cross slide insert is pretty convincingly non circular... which would suggest the start of a thread but the situation with the compound is not so clear.

I have a theory that Faircut liberally borrowed ideas from other lathe makers so I'm hoping that someone will say 'ah, that's exactly like the XYZ lathe'.

Hi Andy , Your insert is so close to the bottom of your cross slide ,Just like mine was at the top which was why I made my replacement the way I did fear of breaking the top of my cross slide , Yours very little room to play with i will watch this operation of yours with interest. I wonder if this has just been pressed in does not like this could have been screwed in . Before i had a lathe. I had a small pulley made for a motor when collected was told this will not fit your motor shaft . Put the motor in the freezer for 24 Hrs Then push the pulley on do not use for 24 Hrs . This I did and it ran for years without any further problem the machine was eventually scrapped with the motor still OK

Good luck Brian

It was upside down when I took the photo but I take your point

If it is pressed in then I struggle to see why it would be worth having a grub screw but who knows.

You mention the deep recessing of the other end, I would then expect any threads in the cast iron to be visible. The only time I have seen nuts like this in threaded housings is if there are two in the hole and there is backlash adjustment. The Smart & Brown model A tailstock has screwed in nuts to Adjust the backlash. There are slots in the outer nut to turn it.

Edited By old mart on 23/06/2020 20:40:12

..well, if iti helps to provoke discussion, maybe they fitted plain slugs and secured them with a grubscrew, and then spotted the thread-centre through the leadscrew brackets after they were fitted-up, in order to ensure alignment.. ..wouldn't be odd for them to come out a bit off-centre..

If they are pressed in, they'd still have to be positively located by a screw/pin/collar to resist the thrust of the screw causing "creep"..

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If the hole is blind I'd pump it full of grease and wind the screw into it. If it's a through-hole I'd wind the screw right in then punch it out with an aluminium drift against the end of the screw.

That's a good idea. At the moment it's all darkness and decades of crud on t'other side but I shall give it a clean and see what turns up.

I doubt there is anything so clever as backlash adjustment going on here.

Hmm... an interesting point... which suggests that I'd need to do the same when making a new one (which is of course the point of all of this). So some sort of transfer punch type of arrangement and then drill and tap (square thread ) in situ.

Not blind. It will need a shouldered punch making up I think. The surviving threads in the saddle insert are paper thin and wont take that sort of force... but no point beating away at a punch if it's threaded so I need to be as sure as I can on the answer to that question first.

Happily both the cross slide and compund screws are 3/8 inch so hopefully I only need to make one tool.

BTW, the saddle in the photo is a 'spare'. The one that belongs to my lathe should have less wear but I'm not intending to mess with it until I know that I can make this work on the 'spare'.

Andy,

There is a solution of thread repair by drilling out the original diameter, tapping a larger diameter thread and placing an insert.

If it is allowd to mention trade names:

Helicoil applies an insert which is some kind of shaped wire that follows the new tapped thread.

Time-Sert applies a thin walled solid insert of which internal thread and external thread have the same pitch.

The latter seems to me more suitable for thread repair where the spindle has to move more or less freely.

Thread for spark plugs is often repaired with the Time-Sert or equivalent solution.

You need special tooling to place the insert and there is also a tool to replace an insert which means that, once you tapped the larger diameter thread, you can easily replace the insert when it is worn.

I have not seen inserts made from brass or bronze.

I have thought of repairing the thread for the spindle in my Emco Compact 5 saddle with a Time-Sert insert.

Edited By Jouke van der Veen on 23/06/2020 21:52:01

Edited By Jouke van der Veen on 23/06/2020 21:56:07

Not much room for an insert. Robert Butler

Thanks. This insert is definitely original rather than a later repair - I have two cross slides, two compounds and two tailstocks which have come from lathes at the opposite ends of the country and they all have the same arrangement.

I guess that helicoils may have been in the back of my mind when I wondered if these inserts are threaded both outside and inside but the possibility that the inside hole was made in situ and may not be concentric is one that I had not considered until this evening.

Definitely a job where it is worth spending plenty of time thinking and asking questions before starting.

Edited By Andy Carlson on 23/06/2020 22:08:40

" The other end is quite deeply recessed in the casting so it's not possible to do any useful measurements there (same on the compound). "

My trick for measuring awkward recesses and holes is to use the shanks of drills or milling-cutters, or other suitable round items, as plug-gauges.

To measure the depth down to the insert if it does not have much rim showing, you could wind the leadscrew in until its end arrives flush with the end of the insert, so giving plenty of land for a depth-micrometer or the tail of a vernier / digital caliper. That may also help show if the insert is down against a shoulder within the casting.

Thanks. A close inspection (...or as close as I can get) of the less accessible side of the inserts is definitely on the agenda for today. Hopefully it will help me to figure out whether the thing is threadded or pressed in.

Time to choose just one of these (spare) items, carefully align and mill out the insert carefully to full diameter of the parent hole (core diameter if that is appropriate). It will soon become apparent whether there is, indeed a thread in there if helical stripes of metal become visible in the hole. I wrote ‘mill’, not ‘drill’, specifically.

Inspecting the bottom of the grub screw hole might also be enlightening?

added to edit.  Another alternative might be to securely loctite a bolt in the thread and apply a large spanner when at full strength?

Edited By not done it yet on 24/06/2020 08:19:17

Just some guesses!

As the thread takes a fair amount of stress as the saddle is worked, I believe it must be well fixed. I don't think there's enough room for another thread. So I suspect a shrink fit, ie a tight insert was forced into a hot saddle sized to give a really strong friction grip when the saddle cooled down. In which case it will have to be bored out.

Another possibility is age related corrosion. This can be better than superglue, and the grub-screw being damaged removing it could be a clue! Heat cycling is a good way of breaking gunged up joints, plus penetrating oil.

I suspect the grub-screw is a crude backlash adjuster, not a fixing. As the insert wears, the grub might be tightened to crush the insert down on the leadscrew. If so, the deformation would also make it hard to get the insert out.

Dave

Edited By SillyOldDuffer on 24/06/2020 09:19:55

Warning: This suggestion may cause outrage amongst conservators

Mill away the cast iron and the insert [inspecting and photographing as you proceed], in the manner of an archaeological excavation.

This will provide clear evidence of the original construction and a convenient recess in which to fit a bespoke replacement.

MichaelG.

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This recent thread may be relevant to to selection of a suitable cutter, if you prefer to avoid creating stress-raisers.

https://www.model-engineer.co.uk/forums/postings.asp?th=162127&p=3

Edited By Michael Gilligan on 24/06/2020 10:22:51

The edge of the casting adjacent to the bush at the 10:00 to 11:00 position looks like it is proud of the surface like the start of a thread being pushed out. This might mean it is threaded. As this is a spare I'd suggest a semi-destructive investigation. If you have a mill start to cut away the end of the bush at it's thickest point. Use an end mill bigger than the thickness of the bush but less than half th diameter. It should be obvious if there is a thread as ou will hit cast iron. A drill or even slitting at an angle with a hacksaw blade (with the height reduced by grinding) would also do.
When removing by whatever method, applicatin of heat will help a lot. A paint stripping type hot air gun is a useful heat source and safer than an open flame.

Robert G8RPI.