Re: [CAD_CAM_EDM_DRO] Alternative shafts for linear bearings

In a message dated 5/18/2003 2:10:48 AM Central Standard Time,
robert.okx@... writes:

> My Question: Are there alternatives to using expensive ground shafts with
> these types of bearings?
>
> I read somewhere (perhaps in this Group) that the hardened steel rod used
> for making drill bits etc could be an alternative.

Robert: Yes, any reasonably-precise O.D./surface-finish HARDENED shafting of
the right dia. will do. If you have only the ball-bushings, withOUT the
pillowblocks they mount in, and must BORE/REAM the holes for the bushings,
you might UNDER- or OVER- bore the holes for the O.D. of the bushing by the
same amount the hardened shafting you have is under or over.

The case-hardened shafting for linear ball-bearings IS expensive, true. But
it is generally VERY precise over its length-sold, and can generally be had
with those "impossible" functions for us tinkerers such as TAPPING through
the case-hardened "shell", etc. Or, center-drilling the softer (machinable)
core of a length 4' or more in length, not good for a "home shop turning
operation"!

The hardened steel rods for making drill-bits generally COMES UNhardened, so
it can be cut and machined with conventional technique, then HARDENED by a
"Heat-Treating Shop" before final sharpening. Too, I have found most "drill
stock" (or ready-to-use!) twist-drill-bits are about 0.002" UNDERsize, as
they ALWAYS bore oversize, at least if used to drill the "WHOLE hole at
once".

I have found even that "expensive" case-hardened shafting will develop
"grooves" where the ball-lines roll, over years, so the use of softer than
RC-60 steel simply won't last useable over a few hundred inches of travel, at
least if your LOADING is within a practical realm! This is one of those
situations where spending SOME money will save you MUCH MORE than that, later
on! Just DO it!

Jan Rowland, Yank Troll


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