Gib Screw Locking Methods

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 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

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

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

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

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.