Tom Senior Advice needed

[ANDY CAWLEYParticipant @andycawley24921]

i have an enormous amount of backlash in my table X lead-screw. I need to remove the bronze nut from the main casting. I have removed the grub screw which was pretty tight and I am now wondering how tight the nut itself is in the casting. My thought is to put the lead screw back into the nut and then whack it on the end with a large copper hammer. Before I go ahead has anybody got advice based on experience with this type of milling machine?”

[ANDY CAWLEYParticipant @andycawley24921]

[Simon Williams 3Participant @simonwilliams3]

DON'T HIT IT!!!!!!!

If you take a look at the ongoing thread Restoration and modifications you'll see someone did exactly that with mine and broke the casting.

To be strictly fair I suspect they failed to remove the grub screw first. But is there only one screw?

Before getting too much into this, what machine are we talking about, and can we have a picture of the problem?

I pulled mine out with a length of M12 studding and some washers. Much more controllable than that horrid hammer.

HTH Simon

edited for link title

Edited By Simon Williams 3 on 09/05/2020 12:39:35

[Brian HParticipant @brianh50089]

Which TS model is it?

Brian

[Simon Williams 3Participant @simonwilliams3]

DEFINITELY DON'T HIT IT!

Re-reading the thread referenced above Old Mart found a second grub screw lengthways.

You might like to read his post on page 3 of the thread, dated 28/08/19 20:56:16. For completeness here's the link again:

Restoration and Modifications

Take care, stay safe

Rgds Simon

[not done it yetParticipant @notdoneityet]

If it is like that other thread, the simple engineering (not ‘fitter with big hammer’ 🙂 ) method might be to place a piece of pipe over the nut, thread a bolt from the end of pipe (through a suitably thick washer), though the nut and another washer and nut on the other end of the feed nut. Tightening the bolt should remove the feed nut safely with no risk whatsoever of breaking anything! Fitting the new feed nut, if a tight fit, would be a simple reversal of the puller direction.

Using brute force with heavy steel hammers on any part of a small machine is both unnecessary and potentially damaging.

edited to get rid of the forum gremlin! and tidy up the grammar😀

Edited By not done it yet on 09/05/2020 14:00:27

[BazyleParticipant @bazyle]

Before leaping in to removing the nut if it is going to be problematic have you considered adding a second nut in a backlash compensating manner?

[Peter Simpson 1Participant @petersimpson1]

As Simon says, use 12 mm screwed rod, nuts and washers to pull the nut out of the casting, beware that two grub screws have not been used to secure the nut into the casting. I renewed both the X and Y nuts last year. Runs really nice now.

[ANDY CAWLEYParticipant @andycawley24921]

Gentlemen I'm not the sledge hammer wielding gorilla my original posting might have suggested, honest!.

I had read the thread that Simon Williams had suggested which is why I asked for advice. Having read what you all suggested I went out to the shed and:-

I had all the bits to do the job, I used 10mm threaded rod 'cos that's what I had. I even got the chance to use a fancy 17mm spanner that I bought in a panic in France a couple of years ago and never actually used. Wound away on the ratchet and bingo, easy peasy :-

I shall send it off to the Ebay chap from Cardiff for him to make me a new one. I'm not confident enough to have a go my self.

As Basyle suggested now is the time to make a back lash wear adjuster. I did one before on my Centec mill but I'm not qiute sure how to do it on a cylindrical nut, I thought I could some how utilise a bit of the old nut. Any suggestions?

The machine is serial number M2481 which believe makes it 1965 so the is some excuse for a worn nut!!

Thanks to you all for your prompt advice, it is greatly appreciated.

Keep smiling and keep safe.

[Simon Williams 3Participant @simonwilliams3]

My apologies we ever suspected an element of "gorilla-ness" might be going on.

Good news you got the bits to come out without mishap.

Do please keep us posted how this resolves.

All the best Simon

[old martParticipant @oldmart]

Good result, Andy, When I encountered that axial screw it was my lucky day, but nobody has ever mentioned more than the normal screw. My way of making the X axis backlash free was the most complicated way imaginable and required a lathe to make two nuts and to add more acme thread to the leadscrew. Not to mention reworking the whole length of the leadscrew to make it even dimensionally over its entire length. Not for the faint hearted.

[Simon Williams 3Participant @simonwilliams3]

Old Mart – good evening.

Does making the X axis back-lash free mean that it is possible to go climb milling?

Best rgds Simon

[ANDY CAWLEYParticipant @andycawley24921]

PpPosted by Simon Williams 3 on 09/05/2020 18:54:28:

Old Mart – good evening.

Does making the X axis back-lash free mean that it is possible to go climb milling?

Best rgds Simon

That is my hope🤞

[old martParticipant @oldmart]

It always helps to reduce the backlash if you intend to climb mill, but it was a lot of work getting the backlash on the museums T S down to 0.001". Even with more backlash, you can climb with caution. Take the normal depth of cut when conventional milling, but when climbing on the way back, reduce the depth of cut to 1/2 or 1/4 and apply a little friction via the axis locks. Climb milling normally gives a better finish, so try to make a climb the last pass.

[old martParticipant @oldmart]

It always helps to reduce the backlash if you intend to climb mill, but it was a lot of work getting the backlash on the museums T S down to 0.001". Even with more backlash, you can climb with caution. Take the normal depth of cut when conventional milling, but when climbing on the way back, reduce the depth of cut to 1/2 or 1/4 and apply a little friction via the axis locks. Climb milling normally gives a better finish, so try to make a climb the last pass.

[not done it yetParticipant @notdoneityet]

Like old mart, I nearly always complete a finishing cut climb milling. With just a tad of depth of cut on the dials cleans up the srface finish quite a lot

[ANDY CAWLEYParticipant @andycawley24921]

I had a look at Old Mart's thread "Start of Tom Senior Refurbishment" and his backlash adjuster and as he says it reduces table travel quite a bit. I had this in mind:-

Forgive the crude sketch, my idea is to have the nut made with as large a flange as I can get away with left on the nut which will be almost slit off; a small amount of metal left which will produce a "solid" hinge. At the opposite side to the hinge there will be a grub screw which goes through the flange and bears against the nut housing. Tightening the grubscrew will take up any slack. The flange will be at the lefthand outboard end of the machine and will only reduce travel by the thickness of the flange.

I hope the terminology is understandable.

 

What do you all think, do not be afraid to be as critical as you like, I'm slightly dubious myself. If it doesnt work I can always chop the extra bit off and it will be a standard nut which served Tom Seniors for a long time.

 

Edited to add my sketch is the wrong way round , the flange should be on the lefthand side to be more correct.

 

Edited By ANDY CAWLEY on 10/05/2020 18:02:21

[BazyleParticipant @bazyle]

How much spare thread is available on the leadscrew and which side of the main nut is it? Is it in the middle or the outside? I'm not a fan of the tilted nut which is used on some lathe cross slides as it means only a small area is taking the wear and in a lopsided manner.

[ANDY CAWLEYParticipant @andycawley24921]

Bazyle, I know what you mean about the tilting nut I frowned when I had to adjust the play on my CVA toolroom lathe the first time but decided if it was good enough for CVA who was I, a mere amateur, to be critical.

I think I see what you're getting at when you ask about spare thread. If the flange was on the righthand side you wouldn't be able to get at it to adjust without virtually removing the table. The thicker I can make the flange the more wear resistance there will be however I'm not an industrial user so that shouldn't be a problem.

[old martParticipant @oldmart]

The design of tilting nut is used on many lathes and mills, but there are drawbacks. The short end will wear out long before the main thread. The wear on your leadscrew will be in the middle where it is used most often, which means that if the backlash is adjusted to work in one part, it will either be loose or tight over the range of X travel. I had nuts in both housings, one being adjustable and had no alternative but to add another 4" of thread to the leadscrew. Just adding 4" of thread was not enough, however, as the uneven wear on the thread had to be addressed. I had to recut the leadscrew thread in multiple passes as the lathe is only 20" between centres. The leadscrew fortunately, being ACME, had a flat top to the threads which enabled soft jaws to be machined for the chuck. Also the spindle bore was just big enough to pass the leadscrew. I had to use a centre in the tailstock and a traveling steady with wider support fingers. Then I made the whole thread equal in "wear" to the centre, so the backlash could be equal along the entire X movement. Actually, it still gets a bit tight at one end for the last 1 1/2", but that hardly matters. The X axis travel is 18 5/8".

Imperial leadscrews are easy to get hold of in the USA, but not here. Kingston engineering can probably help, but a new leadscrew and nut will be expensive.

I have just noticed that your mill has the second housing being used by the power feed mechanism, which would make a second full length nut a no no .

Edited By old mart on 10/05/2020 19:22:57

Edited By old mart on 10/05/2020 19:26:17

[old martParticipant @oldmart]

I haven't done any research as to whether it would work without loosing travel, but having a floating nut which is spring loaded away from the fixed one would work for backlash with a leadscrew having uneven wear. The floating nut would have to have something to stop it rotating with the leadscrew, a collar clamped around it would work. If you had two nuts made and cut one in half to make the floating nut, not only would you have a spare for the floating nut, but the X axis travel would be less affected.

Edited By old mart on 10/05/2020 20:02:02

[ANDY CAWLEYParticipant @andycawley24921]

Belville washers, hmmmm, now there's a thought!

I cant see anything dramatically against the idea, can anyone else?

I would be able to use the old nut if I can think of a way of making a suitable housing. I like the idea in principle all I have to do is figure out the detail. Thats the tricky bit.

[Brian HParticipant @brianh50089]

I have seen an idea on another site which involves making a thin sawcut in the nut and drilling and tapping a couple of holes so that the sawcut can be closed to reduce of eliminate backlash.

Brian

[Simon Williams 3Participant @simonwilliams3]

Not convinced about the Belleville washers idea. It's a simple elegant solution, but introduces elasticity into that direction of that axis. It's got to be elastic or you'd lock the lead screw up solid.

In the direction where the Belleville washer is taking the reaction force from the cutting at the tool, it's a competition between the force to overcome the compression of the spring washer, and the reaction from the cutting forces. It would work OK if you could guarantee never to cut against the Belleville washer, but that's just not going to happen

Rigidity of a machine as all about how steep the stress/strain curve is for the forces resisting that movement at that point in the lead screw. Adding springiness – even if only in one direction on one axis – into the machine is a step in the wrong direction.

We all know that having the cutting forces reacted by positive location is the key to clamping the part successfully, By the same token the leadscrew's function is to provide a controllable and moveable positive location of the work table. The reason climb milling is so dodgy on a machine with back lash is that you don't control the location of the work piece with positive location.

So the squashed up nut is a better option, it has a much stiffer stress/strain characteristic though the point about longevity is well made. Old Mart's description of fettling the leadscrew to have a constant (and therefore correctable) amount of backlash over its usable working length is the corollary.

Rgds Simon

[old martParticipant @oldmart]

My reasoning for using Belleville washers (springs) is to have a compact spring which can be pretty high rating. The main reason for this is because the uneven wear on the leadscrew threads makes any fixed form of backlash adjustment impossible. If you have 0.002" backlash in the centre of the leadscrew which has 0.010" wear, you will not be able to use more than 1/3 of the X axis movement.

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