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Re: Way Wear, Hard Gibs

Marty N
 

Does this mean crossed roller slides on Haas and Mazak turning centers should wear out in a week, rollers hardened to 52 to 55C running on rails equally hard? Open lubrication and flood cooling!

Lathes rarely "wear out" because of use but because of "misuse" and poor up keep. Keep it clean, keep it aligned, keep it oiled, keep it's operation within it's envelope.

Ian, I'm not saying things won't wear. I'm saying the by the time you need to replace a bed because the underside of the way wore out from hard gibs your grand kids will have used it a life time. I adjust these soft gibs about 3 times a year on my HF and about once every five years on my Southbend's hard gibs and it's 51 years old. It's not a question of IF but of when and does when matter if it isn't in your life time. Perspective if you see what I mean. Myself, there is more plus than minus to a set up I can keep in adjustment because of low wear rates and the ability to maintain good lubrication due to good geometry.

John, a friend, who rebuilds a fair amount of machines has a 10" Clausing underway at the moment. He has to replace a broken gib on a cross slide. As a machine shop I asked him why not just "whip one up"? His reply was that by the time he cuts the blank, has it hardened and grinds it in he has more that the $50 it will take to buy it. Yes they have hard gibs and no they don't replace iron castings 5 to 1 because of it.

What's the difference between a current model Honda that will easily go half a million miles between rebuilds and a 60 Chevy that if using today's lubrication might make it 150,000, maybe ( and in the day struggled for 100,000)? Answer! Fit, finish; harder, smoother more precise finishes of all internal components. They run hard as hell chilled iron camshaft journals straight in the cast aluminum heads.

Marty

----- Original Message -----
From: steam4ian
To: 7x12minilathe@...
Sent: Tuesday, March 06, 2007 8:47 PM
Subject: [7x12minilathe] Re: Way Wear, Hard Gibs


G'day Marty,John, Gianni et al.
To extrapolate what Marty is saying suggests a lathe should never
wear out. Unfortunately that is not the case.
The contaminants have to be factored into the discussion. Small swarf
and dust particles will act as abrasives and will selectively attach
the softer material; in Gianni's proposal the cast iron bed.
Journal type bearings have a hard metal shaft running in a soft
bearng shell. The soft metal, Babbit, has the capacity to envelop the
abrasive particles without their abrading the shaft. To use Mary's
analogy the big end bearings, etc have a babbit coated shell. Older
lathes have white metal bearings in the headstock, even some recent
precision lathes.
The world's biggest bearings operate on this principle.
To extrapolate my argument we would be better off using brass gibs
with a babbit coating. (Some Old Timer may recall just such an
application.) Come to think of it, I recall that steam loco cross
head slippers are white metalled (coated with babbit).
Not having any bronze I have made some brass bearing bushes which I
have tinned (97% tin solder), these seem to work well.

For me I would find something better to do with HSS than make gibs
out of it.

One good turn deserves another.
Regards to all,
Ian


--- In 7x12minilathe@..., "born4something" <ajs@...>
wrote:
>
> Yep, you may well be correct - it may be a non-issue. Then again,
> without a pretty good reason, I personally wouldn't do it just to
> find out.
>
>
> John
>
>
>
> --- In 7x12minilathe@..., "Marty N" <martyn@> wrote:
> >
> > Gianni wrote:
> >
> > My idea is to replace the saddle gibs with a pair of HSSco flats
I
> brought in a surplus shop
> >
> > John replies:
> >
> > Flat for those strips is good. I'm not so sure about hard. That
> will ensure the eventual wear will be born by the ways rather than
> the gib strips. I know which I'd rather maintain or replace. :-)
> >
> > Marcello replies:
> >
> > I would not use HSS cobalt flats to make saddle gibs: I fear that
> would mean all the wear will be on the saddle.
> >
> > Marty replies:
> >
> > Hang out for awhile. This starts like it's going nowhere in
> particular.
> >
> > You have a motor with 100,000 miles on it and the rings go south.
> You pull the head and measure the cylinder ridge and find you
> have .005" wear. By extrapolation we could say that .0005" happens
> every 10,000 miles.
> >

> >
> > So here are the questions. Why do we think that tool steel, flat,
> smooth gibs will accelerate wear of the iron bed? Even if it did
and
> did so at the same rate per distance traveled, how long would you
> have to run a lathe to produce 42 million passes over the bed of at
> least 3.5" distance per pass?
> >
> > IF your thinking that there is no correlation between the
examples
> list...you may be right...the lathe has 60 fold greater viscosity,
> runs 530 degrees cooler and does so at something less than 2% of
the
> unit loading. Edge goes to the lathe.
> >
> >
> >
>
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