Gib material - Is brass best?

You'd be lucky to get them made out of Nylon 6 now!

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Yes [often working brass-on-brass] ... and many of them were sufficiently accurately made that they did not need adjustable gib strips.

MichaelG.

Yes. Also clocks are full of brass bearings and I've got an old book that calls bearings 'brasses'.

I'd have thought brass was a good gib material. Takes a good polish and would wear instead of the slide. Possibly ordinary brass isn't thought much of these days as a bearing metal because superior alternatives are available. I don't suppose James Watt could get Phosphor Bronze or Babbit metal. I expect his broadband service was terrible - he lived up north somewhere...

Dave

Are the adjusting screws pointed? if so I would change them for dome shape with the same shape on the gib strip, brass sounds OK for that lathe.

Bearing "brasses" are actually bronze.

I fancy it all depends on surface speed multiplied by loading, so for something very slow and lightly loaded ordinary brass will give a good service life. Up the speed and the load (i.e. main bearings in a traction engine) and ordinary brass isn't hard enough to resist the friction of the load it is supporting.

I don't know much about clocks, but it seems from the little I've seen that the bearing surfaces, if brass, which carry the load of the mainspring etc wear oval if left long enough, whereas up by the escapement the forces are very much less and the bearings' service life is much better.

Local surface finish and hardness of the supported surface is also going to have a bearing (sorry!) on the service life.

Is brass best?

The answer to the original post is 'no' but it will work - probably just as well as some other alternatives. As soon as gibs allow any lateral movement, there will be a considerable force applied by the machine across the slideway. That may accelerate the wear on the gib/slideway. Think here white metal bearings for crank pins. Lead/tin white metal is suitable for petrol engines, but diesels require something a little harder - more tin, some antimony and, latterly, indium as well.

Perhaps the gib might wear rather than the slideways initially, I don't know, but likely a steel gib would give better/longer service life overall. Microscopes don't have any lateral loading, so not really comparable, I would think. As far as I know bearings were brass, unless bronze was substituted for a good reason. Slow moving, large area, well greased and easily/cheaply replaced. I know that bronze was used, in preference to brass, in disc coulters on ploughs, probably due to the side loading, but perhaps because of the harsher environment.

But get the right type of brass, as there are several and some are better than others for different applications.

I've always used gauge plate for gib strips. Not the easiest material to work with but seems to do the job OK at least with cast iron.

If you look on various mini-lathe forums it seems brass gib strips is a common modification that apparently works for them. It's a low speed , low load application so material spec is not real critical. Not like on a motorbike main bearing etc.But a strip of bright mild steel might be easier and cheaper to obtain and will work just.fine, as on most lathes ever made.

When the cast iron/ Chinese cracker carriage gibs cracked on my mini-lathe (as many others have found out it is weak spot waiting for a heavy hand) I made replacements from 6mm brass plate and after many years they are still working well with the odd tweak when chasing down a chattering problem during parting-off.

The chattering was mainly due to operator error and loose top-slide clearance. I checked this by putting a DTI on the bed and leaning hard on all the moving bits until the clock gave me something worthwhile to investigate.

Diamond lapping and carbide paper dressing the moving faces (gibs and bearing faces - the bearing faces were quite roughly finished, tailstock similar) improved things nicely and inserting 1.5mm ball bearings under replacement cup-pointed gib adjusting screws got things moving nicely.

I used bearing blue to check the progress but am not experienced at scraping so just used it as an indicator.

* Danny M *

Having googled, I learnt that normal gib strips are quite big. The gib strips on the Simat are 2mm or less thick.

I've been rummaging in my scrap box for sheet steel I can cut some strips out of. I have some pressed steel parts from an ink jet printer that look promising.

I have read that the Simat top slide (held by a single hex bolt) is not very rigid, and best removed (if you can manage without it). I have evidence that "someone" took this seriously. In my "bits" pile I had a small slide, that I was going to use as a focusing/traverse for focus stacked macrophotography. On close reinspection it's the top slide from a Simat!

BugBear

Edited By bugbear6502 on 30/10/2017 13:02:29

http://www.model-engineer.co.uk/forums/postings.asp?th=51850

A lot of sheet metal is very ductile steel, so that it can be pressed to shape easily. This means it would bend easily in use where the gib screws press. It might be worth purchasing a piece of gauge plate the thickness and width you need. It is a higher carbon steel, quite rigid, ground flat on both sides and ideal for gib strips. It is commonly available in circa 500mm lengths quite inexpensively.

I fitted brass gibs to my little Meteor II instead of the plastic. I also pinned them and it seemed to me to feel better.
It's not a major operation, try several materials, see what works best?

Just for comparison, the gib strips on a Super Adept, that paragon of British Quality Engineering, appear to be from unfinished 1/16 x 3/16" or 1/4" black steel...

You mean it's just like, hacked off either end? sounds like a very british thing to do, id say.

Natural for a UK engineer to get hacked off, we were always the end of the line.

Seriously gib material should be softer than the mating material. Hardened ways can use cast iron gibs, cast iron ways can use soft steel gibs or in the case of small lathes even brass. Materials shouldn’t be able to be deformed under pressure as this negates any chance of constant pressure.

If that were true, why have all my Myfords (an ML4, two Super 7's and a Speed 10) had hardened steel gib strips along with my Emco Compact 5, Zyto and Cowells ME lathe? They're all hardened steel running against cast iron.

Edited By Chris Trice on 08/11/2017 00:03:02

..... except the Compact 5 which is hardened steel running against Mazak.

If the OP had set his question as simply 'which material is best? ' rather than 'is brass best? he would have received better replies.

A bit like 'is carbide best?' for cutting tools rather than an enquiry as to which material is best. Often 'horses for courses', so no best for all situations.

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The opening post seemed very reasonable to me ... and has elicited some good replies.

MichaelG.