Re: Alternative shafts for linear bearings

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "robertokx" <robert.okx@s...>
wrote:

> Whilst scrouging around a scrap yard I found a dozen or so new

nippon

> bearing company linear motion bearings(16mm ID & 13mm ID).Up until
> now the idea was to go with rollerskate bearings on angle iron for
> all 3 axis.
> 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.
>
> Thanks
> Robert

McMaster does have Grade 01 Tool Steel "Precision Ground" Drill Rod -
Metric Sizes (page 3370)... $8.36 for 3ft of 13mm and $11.23 for 3 ft
of 16mm. The problem is, even assumming it's straight enough for
your use (it's not specified), the diameter tolerance is +/-0.025mm
and linear bearings do not fit plus size. You could pray that the
ones they send you fall on the minus side, but Murphy's Law will
probably prevail and your bearings won't fit.

If the bearings you've obtain are not open type, you'll only be able
to support the shafts at their ends, and with 13mm and 16mm diameters
this will greatly limit the length you can use. The GOOD part of
that is that it keeps the shafting cost down. For some reason, 13mm
hard shafting costs double (in McMaster at least) what even
substantially larger sizes do, but a single 500mm piece ($35) could
be cut in half for a short Z axis. For the 16mm, probably the max
shaft length end-supported, even for light router use, is about
500mm... at $16.28 each, two pieces for the X and 2 pieces for the Y
axis wouldn't be too bad... all the stuff you'd need to implement
rollers on angle iron isn't free (bearings, shoulder bolts for axles,
bracketry with adjustability, etc.).