Gib Screw Locking Methods

[old martParticipant @oldmart]

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.

[John HaineParticipant @johnhaine32865]

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

[John HaineParticipant @johnhaine32865]

"Tekelec"….

[DiogenesIIParticipant @diogenesii]

Posted by Dr_GMJN on 01/11/2020 14:05:10:

I’ve got hex. Socket grub screws on the mill. It’s the same issue, but using different tools. In fact I found it’s even worse unless you use hex tool bits – a standard Allen key has so much movement in torsion it’s not even funny…

..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..

[Dr_GMJNParticipant @dr_gmjn]

Posted by DiogenesII on 01/11/2020 21:00:19:

Posted by Dr_GMJN on 01/11/2020 14:05:10:

I’ve got hex. Socket grub screws on the mill. It’s the same issue, but using different tools. In fact I found it’s even worse unless you use hex tool bits – a standard Allen key has so much movement in torsion it’s not even funny…

..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.

[oldveloParticipant @oldvelo]

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.

[Dr_GMJNParticipant @dr_gmjn]

Posted by oldvelo on 01/11/2020 21:23:12:

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.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by DiogenesII on 01/11/2020 21:00:19:

Posted by Dr_GMJN on 01/11/2020 14:05:10:

I’ve got hex. Socket grub screws on the mill. It’s the same issue, but using different tools. In fact I found it’s even worse unless you use hex tool bits – a standard Allen key has so much movement in torsion it’s not even funny…

..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..

.

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.

.

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

[oldveloParticipant @oldvelo]

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.

[DiogenesIIParticipant @diogenesii]

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.

.

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..

[Dr_GMJNParticipant @dr_gmjn]

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.

[John HinkleyParticipant @johnhinkley26699]

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

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Dr_GMJN on 02/11/2020 08:51:05:

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.

[…]

.

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

[Dr_GMJNParticipant @dr_gmjn]

Posted by John Hinkley on 02/11/2020 09:04:34:

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

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).

[John HinkleyParticipant @johnhinkley26699]

Posted by Dr_GMJN on 02/11/2020 09:14:27:

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

[Dr_GMJNParticipant @dr_gmjn]

Posted by John Hinkley on 02/11/2020 09:35:33:

Posted by Dr_GMJN on 02/11/2020 09:14:27:

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.

[not done it yetParticipant @notdoneityet]

Personally, I find it needs patience (more than ‘a little’ at times) and a good degree of fiddling around to get gibs set satisfactorily.

Except on new machines, the settings can be a compromise – but the same system has been used for well over a hundred years and (as far as I can see) ‘it ain’t broke so dunt need fixing’.

I expect skilled operators, who actually know their way around machines, can get the job done quite easily and effectively in quite a short time.

[John HinkleyParticipant @johnhinkley26699]

Posted by not done it yet on 02/11/2020 10:12:16:

I expect skilled operators, who actually know their way around machines, can get the job done quite easily and effectively in quite a short time.

I couldn't agree more, but for those of us who have had no engineering training and are, for the most part, self-taught, I see no reason not to make it an easier job to accomplish. Maybe if everybody had the admirable attitude of "if it ain't broke, don't fix it", then we'd all still be galloping up and down dirt track roads in carts pulled by horses!

John

(Can't find a leg-pulling emoji!)

Edited By John Hinkley on 02/11/2020 10:34:33

[Dr_GMJNParticipant @dr_gmjn]

Posted by not done it yet on 02/11/2020 10:12:16:

Personally, I find it needs patience (more than ‘a little’ at times) and a good degree of fiddling around to get gibs set satisfactorily.

Except on new machines, the settings can be a compromise – but the same system has been used for well over a hundred years and (as far as I can see) ‘it ain’t broke so dunt need fixing’.

I expect skilled operators, who actually know their way around machines, can get the job done quite easily and effectively in quite a short time.

I don’t pretend to be a skilled operator, just someone who’d rather spend their hobby time making parts rather than adjustments.

[Clive FosterParticipant @clivefoster55965]

Dr_GMJN

Interested to see that you decided to have a small clearance between the top of the gib and the slide recess.

When I started doing such modifications I considered that the combination of a locating dowel and fitting the gib snugly against the top of the recess would pretty much remove any locating forces from the adjusting screws. Seemed that the system would be better behaved and much longer lasting when the adjusters only had to deal with setting clearance.

Thinking about things fitting it your way with a slight clearance lets the gib float sightly into its best alignment rather than being strictly constrained by fitting and machining accuracy. Potentially giving slightly tighter clearances and smoother working than my way, unless the fitting is essentially perfectly accurate.

Out in the real world such differences are probably moot. How good the workmanship and how well the job is done being probably more important than details of the method. Going for a small clearance is undoubtably makes it easier to do a good job so its probably the better method in practice.

Hmmn. Looks as if I could have saved myself a deal of fretting and extra careful work over the years if I'd thought it through!

A flat, angled pusher provides no location capability and does require the gib to be both dowelled and pushed up into the top of the recess. The pusher does remove the requirement for accurate registration of hemispherical end of the screw with the conical recess. Possibly better engineering but it needs sufficient casting depth to accommodate the pusher. Ideally the pusher should work in a plain bore so the threads ned to be drilled out and either re-tapped or an insert fitted. More work I think.

However the gib modifications are done the GHT thumb lever lock screw is a desirable addition.

Clive

Edited By Clive Foster on 02/11/2020 12:14:01

[Clive FosterParticipant @clivefoster55965]

NDI

The common floating gib located and adjusted by pointed screws in dimples is indeed generally satisfactory when a machine is new and continues to perform well when lightly worn. Especially if well maintained. However it is subject to wear over long life and vulnerable to ham fisted adjustment efforts.

From a manufacturers viewpoint its a relatively inexpensive system to make with relatively basic factory equipment. The "works well" period is likely to outlast both initial buyer and second user ownership. Given the need to match price / performance ratio against the depth of the first purchasers pocket it's an effective engineering choice. Spending on a more expensive system that will still be working perfectly 40 + years and several owners later is pointless.

Given appropriate investment in machinery taper gibs are at least price competitive and, possibly, cheaper than simple screw adjusted gibs. Which is why they now seem to be the norm. But you have to be able to afford the machines.

By the time folk like us have issues with gib adjustment the machine will inevitably be at least somewhat worn. The improved gib location given by dowel location and hemispherical ended screws working in accurately aligned conical recesses significantly improves the ability of the system to cope with wear elsewhere on the slides.

From Home Workshop guy or gal with an older, inevitably somewhat worn machine, perspective an afternoon of careful work is a much better price / performance ratio than obtaining a replacement machine. Even neglecting the negotiations needed to get the requisite expenditure past the domestic authorities!

Clive

[Dr_GMJNParticipant @dr_gmjn]

Thanks Clive,

Yes, the decision to give a bit of clearance at the top of the gib was entirely due to me having to drill my own location dimples. With the best will in the world, these would never be perfectly aligned with the screws no matter how careful I was, and the screws won't be perfectly straight either, to the tolerances we're talking about. I wanted them to be able to find their own best-fit seating without adding a further constraint.

I believe the dimples are there purely to stop the gib from moving left-right.

Regarding fettling old machines, I agree. I just hand filed a 0.002" wear dip in the front slide of the ML7, and converted it to wide-guide:

https://www.model-engineer.co.uk/forums/postings.asp?th=168005&p=4

This is why I bought the new gib in the first place; to eliminate another source of out of flatness.

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