Gib material - Is brass best?

In my tweaking of my little Simat 101, I was trying to make the slide rest move better (and conversely, stay still better).

I discovered that the gib strips were some kind of delrin/tufnol type material, and were nearly pierced completely through by the adjusting screws.

Should I attempt to find one-for-one replacement, or would brass (easier to obtain, in any case) be an upgrade?

BugBear

I should think brass would be an upgrade from warped and distorted Delrin. But steel would probably work just fine as it does on most lathes.

You want the gib to spread the load a bit over an area rather than be little better than the point load of the screw. So it depends a bit on the thickness whether brass will distort. You will probably be ok if you can fit >2mm in the gap.

Brass is next to useless for a sliding bearing, it just wipes leaving brass dust behind. You would be better off with steel, so long as it is lubricated. Tufnol is a brilliant wear resistant material but (to quote the late and great JS) you have to use the right grade of tufnol (iirr the woven one) and it has to be loaded in the correct orientation to the fibres. Do you have anything bronze telated, probably doesn't matter which grade? Failing that I'd choose ordinary mild steel.

Edited By Simon Williams 3 on 27/10/2017 13:15:33

I stand corrected; in truth I was speaking from a part-memory that (in wood working tools) brass adjusting nuts on steel bolts are used because of low friction, so I extrapolated that brass/steel is a good sliding combination.

BugBear

As it is most likely your machine ways are made of cast iron which is an inherently slippery material then steel will be ok as a complementary material. I don't think you need to mix two slippery materials.

Mike

Ground flat stock, which is available in many sizes is the best, its flat and very smooth. Have used it for gibs many times.

A long time ago, still at school, (1970 or thereabouts) in Stroud, not that has anything to do with it, I persuaded the metalwork teacher (there's a strange concept in this day and age) to allow me to make a new main bearing for my Triumph Twin. The non drive side was a plain bearing, I had a lump of brass, what could possibly go wrong.

He did warn me that my lump of brass wasn't the right place to start, but young and arrogant as I was I wasn't having any truck with that. I spent ages making a new bush, also grinding the end of the crankshaft true and round. I remember being told off for leaving the school's one and only 1 - 2 inch micrometer in the suds in the lathe drip tray - which was by this time awash. I enjoyed every minute.

Installing the bearing was easy peasy, bolting the crankcase back together the work of a few moments, jump on the kickstart and all was hunky dory. Brmmmmmmmm! Deep Joy.

For maybe five minutes.

The brass bearing was in bits in the oil, my crankshaft was flapping about in the breeze, long faces and wall to wall despondency.

So. Lesson learned, green brass is a lousy bearing material.

Gauge plate is a much more workable suggestion. Not that it would have fixed my Triumph, but I guess that's beside the point nearly 50 years later.

It may have been built with a plastic gib (having been sold as a kit), but that probably isn't optimal for the size of the lathe. If you've got more than 1/8" of space for the gib, try to use cast iron. If less, then use mild steel or gauge plate, depending on what you have available. Try to use all the available space to give as thick a gib as possible. This will improve the load distribution from the adjusting screws and make things stiffer (in the 'tippy' sense, not the 'slidy' sense).

Hard brass will be fine for something like a Simat.

Neil

Just out of interest - I've got a strip of steel with a brass 'face' on one side which I'm sure I was told was for use as a gib strip (can't recall the details now). Am I recalling this correctly and what would be the pros/cons of that approach in the Jurys opinion?

Regards,

IanT

Ian,

I hope this doesn't muddy the waters too much but I have been told (more than once from different sources) that brass has a 'sponge' like behaviour that is good for absorbing point pressure and shock. It might not be great for a high speed bearing but a gib is obviously not a high speed bearing.

Phil H

I would use steel to slide against cast iron. Colin

For what it is worth, my little Multico morticer has a solid yellow metal gib on steel slide.

.

24 carat ?

24 carat gold is rediculously soft. Lower carats with the right alloying metals might last a while, but definitely not 24 carat! You don't need to drop a 3.5kg pure gold cone very far to very much flatten the tip considerably. Seen it done!

Edited By James Alford on 28/10/2017 18:51:41

Michael Gilligan:

I was trying to indicate that I don't know what my gib was made of but that it might have been brass. This is the kind of information we would like but that manufacturers often fail to give; the Multico literature just says "precision dovetail slides" (to their credit, they say "mortiser" rather than morticer - cf practice and practise).

Apart from the fact that the forces in a lathe slide act differently, a solid gib is, of course, doing a different job from the OP's strip gib.

.

Please forgive my flippancy ... But, in my defence 'Yellow Metal' is a commonly used term for Gold, as well as for a specific composition of Brass.

MichaelG.

Just a thought, but weren't most microscope dovetails in brass in the good old days?