Gib Screw Locking Methods

When I made an improved cross slide for my Starturn lathe I made the arrangement as shown in these two pictures.

I made pushrods with combined dowels and angled faces to give better support to the gib strip. I think I applied some superglue to the threads of the grub screws and let it set before fitting them, to make them self-locking.

Martin.

Hmm.

Fit push-rods yes, but I'd not have locked the screws with glue! That's replacing a possible problem now with a definite one in future.

Cross-slide gib screws tend not to work loose, at least I have not encountered it, but anyway a much better approach is to use longer screws and fit them with lock-nuts, as on my EW lathe..

I used that on my Drummond manual shaper whose action combined with some wear did slacken the screws. This succeeded, and I can still adjust them if necessary.

.

Don’t Panic

[quote] ... I think I applied some superglue to the threads of the grub screws and let it set before fitting them, to make them self-locking. [/quote]

My emboldening for emphasis.

MichaelG.

John - I think you won the internet today!

I cross-drilled the screw threads and...basically what you said:



Also polished the hemispherical ends of the pins, and drilled the new gib. I used a transfer punch - the length of the threaded holes means it pretty accurate. I also put a strip of card on the top edge before marking to ensure a bit of clearance above:



It works absolutely beautifully - just turn the screws until no play and the drag feels right, and leave them. No pratting about with lock nuts. Perfect.

Thanks!

Edited By Dr_GMJN on 01/11/2020 18:36:47

Smart & Brown use a low profile design, with the locknuts pretty much flush with the surface. A tubular spanner is used on the nuts and a screwdriver or hex key is used on the gib screws.

The only tapered gib on the S & B model A is for the sliding leadscrew nut.

There used to be aa design of adjusting screws for microwave cavity resonators, generally known as "Telelecs" after their manufacturer. These were threaded "grub" screws with two sections of thread separsted by a reduced diameter "waist", into which were cut a pair of slots from opposite sides, going perhaps 75% of the way across. The threaded portions were cleverly made so the threads were slightly displaced from one another. When you screwed the thing into a threaded hole you hade to press axially to slightly shorten the screw to make the second part of the thread ine up with the internal threads to be able to continue to screw it in. When this pressure was released the threads would spring apart again and lock. This completely obviated the problem of a locknut fighting the adjusting screw. If you thing adjusting gibs is hard, try tuning a microwave filter which has locknuts on the tuning screws!

Edited By John Haine on 01/11/2020 19:53:10

"Tekelec"....

..Been mulling this over a bit - there doesn't need to be that much torque used to ?lock the nuts - they only need a light nip to stop the screws loosening - the whole operation only requires the tips of the fingers - once you can feel that some friction is present, thats enough..

Yes, but once you've found the exact rotational position of the screw, you have to stop it turning either way even a fraction of a degree. Trying to do this with a screwdriver of allen key while you lock the nut is a pain, and then even if you can do this, nipping the lock nuts can pull the screw back in itself, messing up the adjustment.

I can't see any issue with the nyloc method - simply adjust the screw and leave it. Time will tell of course, but so far so good.

Simple solution to the play of an allen key in a socket head screw is to exert pressure toward the screw at a right angle to the rotatation then do up the lock nut.

It's not just the play in the head, it's the lack of torsional stiffness of the allen key itself, especially the smaller ones. That's why I always use an allen head socket bit, in conjunction with a tightly fitted adjustable spanner. Still a pain in the arse though.

.

Just remembered a neat little tappet adjusting tool from years ago ... it should be possible to make something similar to work with lock-nutted gib screws.

MichaelG.

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Edit: Mine was by SPQR, but I think later ones are Gunson

... for our purposes we wouldn’t need the ‘click’ but the basic layout looks good to me

Edit: I’ve even found the patent 

https://worldwide.espacenet.com/patent/search/family/010318387/publication/GB1293866A?q=spqr%20tappet%20adjust

Edited By Michael Gilligan on 01/11/2020 22:16:06

Edited By Michael Gilligan on 01/11/2020 22:20:57

I guess the point I made was not explained properly that I use good old fashioned "L" shape Allen Keys to adjust gibs and the Ring end of a ring open end spanner on the lock nut. No excess torsion spring forces required.

Just remembered a neat little tappet adjusting tool from years ago ... it should be possible to make something similar to work with lock-nutted gib screws.

MichaelG.

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Edit: Mine was by SPQR, but I think later ones are Gunson

... for our purposes we wouldn’t need the ‘click’ but the basic layout looks good to me

Edit: I’ve even found the patent

**LINK**

I didn't even know Sykes-Pickavant had a factory in Rome..

..Gunson still make them, (P/N G4094).

If I wanted one to experiment with, I'd look for a used SPQR one from a private seller - these items were a staple of autojumbles and "tat" stalls at rallies when we had such things (and we'd miss these people too, wouldn't we?), I think they're currently changing hands for about a tenner..

I doubt the Gunson's tappet tool would make much difference - you're still tightening a nut against a stud/block, and the associated pull-back is half the problem.

My lathe had 0.002" of local wear on the front bed, and that was enough to lock it and prevent full travel towards the tailstock. So if we assume the gib adjustment needs to be of a tolerance significantly less than that, you're back to trial and error in tiny increments.

Eliminate the nuts and you eliminate that issue (I've already proved that by using the nylon insert method - all four screws set in under a minute). The only question mark is how stable the setting will be with use over time.

I'm pleased that the nylon wheeze seems to be working for you. I surmise that there shouldn't be much drop-off in the holding capacity, since there is relatively little, or no, movement of the screws unless you are constantly fiddling with the gib alignment. Should the nylon lose its grip, it is but a matter of moments to whip the screws out and replace it (at minimal cost ). That's what I call a result!

John

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I fully accept that alternative locking methods are available [and I already use them] ... but I was trying to offer an improvement upon your previously referenced tooling:

[quote] That's why I always use an allen head socket bit, in conjunction with a tightly fitted adjustable spanner. [/quote]

MichaelG.

Edited By Michael Gilligan on 02/11/2020 09:15:38

John, there is a potential issue with any slight movement of the gib strip working to loosen the bolts. I expect it would be a bit like a badly designed bolted joint, where any relative movement between components can loosen the fasteners. Depending on the forces involved, a Nyloc wouldn't necessarily stop this (nor would most other "locking" methods).

I get your point. I suppose time will be the final arbiter. I await the long-term outcome with interest.

John

Same here! If it doesn't work out, nothing's lost, I'll just mess about with the lock nuts again. They're still there, just not tight.