Making a gibstrip, how to?

Is there a good explanation of how to construct a gib strip? What material to use? I have poked a bit around on line and have never found a good discussion.

For example should the gib be harder or softer than the material it is against?

Should it be smooth, or have channels for oil?

How tight should it be. Should there be holes for the tighteners, drilled before or after machining. Stress relief?

Would there be considerations for production machines vs hobby machines?

Brian S

Edited By JasonB on 10/03/2015 17:10:44

I've used both black mild steel, machined all over and very hard (not engraving) brass, the brass works really well.

Neil

I have made gib strips from brass. Given a dovetail slide, one way to make the gib is to clamp the slide on the mill table, with the dovetail facing up and set parallel to the axis. Clamp the blank strip into the dovetail using a piece of parallel steel bar in the vee between the blank and the bottom of the slide with toolmakers clamps. Machine the top. Then turn the blank over, with the now angled face on the first side resting in a piece of shim on the bottom of the slide and machine the second face down very nearly to the top of the slide. Job done, if that makes sense.

I really like that idea. Would not the "nearly" though cause an issue rubbing against the way? Perhaps elevate the second cut with a shim at the bottom of the dovetail?

So I understand using Brass for the gib..easy to machine..etc ...but is this the best idea? Would friction be an issue? Teflon coated ?

regards

Brian

Always a softer material so it wears in preference to the slideway. Brass on small machines is best but large industrial machines might use cast iron.

A reasonably good finish so it doesn't sit on peaks but not mirror smooth as that would expel oil and become "sticky"

Oil grooves are fine if you can actually get oil into them otherwise a bit of grease will do.

Holes? Some spot faces or hemi-spheres so the screws stop the strip from sliding out. Just tight enough to stop any sloppyness.

I made the gib strip from bronze for the taper turning attachment on my Smart and Brown lathe. The original, which was missing when I bought the lathe, was also made from bronze. It runs on the steel taper turning guide.

The easiest way I have found for making gibstrips is to cut then with a slitting saw from a plate of material held in a tilting vice. The advantage of this is that the cutting forces are low if you take small cuts and the reaction force to the cutting is along the axis of the plate and hence bending of the plate is minimised. The only thing to be careful of is the plate must be fully annealled or hot rolled. If you use cold rolled material any strip cut from the edge will be bent by the relief of internal stresses.

If the gib is running against cast iron then steel or brass are both good materials.

Mike

Brian, that's why I mentioned the shim! I think I used .5 mm Ali and machined the second face to probably .25 mm above the slide, so the finished gib clears by .25.

You know,,, I don't know how I missed that on the first time through, guess my mind started racing on the idea,

regards

Brian

Regarding the "use a softer material so it wears rather than the slide" comment. Does this really work or does the soft material pick up grit better, turn itself into a lap and proceed to wear away the slide anyway. Brass wheels always do this to steel pinions on clocks for this very reason. Admittedly slides could arguably be in a cleaner environment. Be interested in anyone elses take on this.

If you have Harold Halls book "Milling, a complete course" he gives the process.

regards Martin

At Dean Smith & Grace Ltd. earlier, short type cross slide gib slips, that were one screw adjusted (diamond shape in section) from the rear of the slide, were made of high grade cast iron. The later long type cross slide that had multiple cap screw fixings and grub screw wear adjusters were made of EN 3 or equivalent. The slips were supplied from stores in incremental sizes ( plus .010", .020", .030" and so on ) rough machined. The cast iron slips although more difficult to hold because of their shape, were by far the easiest to scrape. Steel slips were far more time consuming to scrape and fit and I was always disappointed with finish that could be achieved. All fixing screw holes and adjusting dimples were marked from the slide. Oil feed grooves were marked and grooved from oil nipple holes and varied in design from short vee type to long zig-zag type. Tightness should be firm, not tight and allow the slide to move with slight drag.

.

I agree completey regarding the principle, Martin ... also demonstrated when a gudgeon pin wears, instead of the little-end bearing.

It would probably be very relevant to those that do grinding; but hopefully less so when producing swarf.

MichaelG.

. . .L and king pins and shackle pins on old cars.

Russell.

But if the material is soft enough, the particles embed completely - think white metal big end bearings.

Neil

Every gib strip on all my machines are some form of steel, tapered rhombus shaped with screws at either end to adjust. They need to be perfectly flat, precise and smooth as silk no oil ways.

Pretty sure lathe cross slide is a decent casting, its broke a few times mid job. Didn't fancy the cost and no time to faff around making I usually weld up with inherent warping, file and diamond stone it back in.

The multi pinned rhombus style as used in Myfords dead easy, anything will do as long as two rubbing edges are parallel.

Its been a long time since done any pro scraping after a full precision regrind. Only time it was done was where punter requested as it aids oil flow but detrimental to wear ie less contact area. Funny almost every scrape job ever seen customer stating ive only took a couple of thou off turned in to 10 of thous to put right, its a fine art.

The comment on Myford gibs aroused my curiosity...not owning a Myford. The design of the gib is a bit different, I can see how the "rhombus" shape allows tightening. This brings up another question. The gib strip on my lathe is a flat piece of material running between two 60 degree angled dove tails. There are a series of tightening screws spaced ~5cm. Now when tightening these, would not force be on the screw point, as opposed to the side of dove tail? I can see having two gib strips that are wedge shaped, being pushed at the ends to create a constant force along the gib, but that is not what I have. Just curious what the analysis is on point contacts tightening the gib. The Myford design would appear to cause a constant force along the gib as well.

Lots of good discussion

regards

Brian

Interesting discussion by Dan Gelbart that touches on a few of the comments mentioned.

https://www.youtube.com/watch?v=cwdoUjynpEk

Opinion is that scraping is better than grinding, I always thought the other way around but the evidence is persuasive.

As well lapped, or scraped surfaces will not wear due to hydrostatic fluid between...now can that be applied to a gib?

regards

Brian

Curl scraping.

Large gibs such as the table of a mill will have oil grooves but smaller ones get scraped in curl patterns. These curls become pockets where oil can be retained. This is done after machining.

It takes a lot of practice to get the technique.

All gone now as slideways are mostly a thing of the past. Linear bearings are cheaper and quicker but not as strong.