Re: extrusion of Linear Bearing pillow block question...

Hello again,

As I posted before, many of the newer "round rail" type linear
bearings RELY on the bore of the HOUSING to meet their specs!

The load is transfered to the steel plates, which are held in
POSITION by the plastic housing. These steel plates in turn, bear
upon the housing. On Thomsons' super smart series, these plates
are "rounded" to allow for misalignment(s). The down side is that
this means EVEN MORE of the force is concentrated on EVEN LESS area
of the housing, making its' precision/hardness even more important.

SOME older types can be used in "sloppy" housings, as the steel body
is thick enough to carry the load. However, these tend to be the
precision types, and are typically very expensive.

But you just don't get precision for free...

Lastly, most of the higher precision ball bushings(a Thomson trade
name for round rail recirculating ball linear bearings) use a
locating pin to fix axial/rotational position in the bore. this is
done to prevent misalignments from "twisting" the loaded bushing.
Twisting a loaded linear bearing of this type is VERY bad for it!

Hope this helps.

Ballendo


--- In CAD_CAM_EDM_DRO@y..., Randy Gordon-Gilmore <zephyrus@r...>
wrote:

> At 10:20 AM 2/17/02 -0700, Smoke wrote:
>
> >I would not use a press fit! I'd use the bore tolerances

recommended by

> >Thompson in their catalogs. If necessary, I'd buy a reamer sized

to these

>
> Absolutely right, Smoke! The recommended bore for the Thompson

3/8" i.d.

> Super Ball Bushing (the size I recently used) is .6255/.6250"

These things

> are not very tolerant to sqeezing or misalignment. And that goes

for

> torquing *after* they're mounted. The best thing, in the
> slightly-oversized-hole-with-Loctite case, would be to assemble the

whole

> carriage/knee/whatever assembly and then Loctite all the bearings

at once,

> so they at least have half a chance of seeking a common alignment

to the

> shafts they're to run on.
>
> Best regards,
>
> Randy
>
> Randy Gordon-Gilmore ,----.___________ ______________

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