Re: [CAD_CAM_EDM_DRO] extrusion of Linear Bearing pillow block question...

Since you ask....

First I wouldn't use an extrusion. Castings can be made a LOT
cheaper....unless your doing them by the thousands. For $10 bucks worth of
propane, I could make a lot of castings all at one time from scrap aluminum.
These would have the flanges cast in place as well as a cored hole for the
bearing. If I didn't want the hole cast in place, I could cast long bars
and saw them to desired lengths. If I were to cast them using lost wax
process, I'd cast long bars with a cored hole for the bearings.

I'd machine them in three steps on the mill using quick change tooling.
First I'd set the casting upright for machining the end (face milling), the
bottom mounting surface (side milling) and the bore. The bore would be
drilled and reamed. This method insures the bore will be parallel to the
mounting surface as well as square to the end of the part.

The part would then be turned over for machining the opposite end. Then the
part is rotated bottom end up for drilling the mounting holes.

If I had to do hundreds of parts I'd do it a bit different. I'd build a
fixture that would allow me to do all the machining in one setup. With some
forethought, the fixture could be build to hold more than one part for
machining in multiples.

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
tolerances. I'd use clips on the ends to hold the bearings in place.
That's what the grooves on the ends of the bearings are for. If the
bearings do not have these grooves, I'd ream the bearing hole to a depth
that would leave a retaining wall on one end. Then I'd tap a hole on the
other end for mounting a retaining clip.

Some years (lots of them) ago when I was first learning to use a lathe, I
made a special aluminum bushing for some roller skate wheels. I bored the
hole a tiny bit too big. So I experimented with something then available
called Loctite Bearing Mount (no longer available). I put in a few drops,
slid the bearing in and heated it with a match. After heating I couldn't
get the bearing out even using a 3 pound ball peen hammer and a BIG punch!

You don't really need stock bedding compound for holding the bearings in
place. There are lots of epoxies (five minute epoxy comes to mind) available
at the local hardware store that will work just as well. All you need to
remove the bearing when using those is a little bit of heat. Naturally,
you'd need to be careful not to get any epoxy inside the bearing, so don't
use very much if you go that route.

If the bore is a "crummy fit" (oversize), don't bother trying to fix it by
using epoxy. Epoxy is not a good substitute for good workmanship! Chances
are the bearing will not achieve proper alignment. Throw the defective part
out and make one correctly.

Set screws of the dog point variety will work, if the bearing OD is provided
with a hole, slot or groove for the purpose. You just need to be very
careful not to run the screw in too tight. After adjusting the screw it
should be locked in place with another screw or a jam nut. I'd prefer not
to use set screws as they are not "idiot proof" enough.

Smoke

> Hi Lloyd:
> Setscrews are a bad idea on bearings.
> The one-sides pressure will misalign them at best, and distort them at
> worst.
> Circlips are the way to go if you can't achieve a press fit within an
> ACCURATELY round bore.
> A way for crummy holes ( but not TOO sloppy) is Loctite, (and a hammer

when

> you need to service them!)
> Another really good way for lightly stressed applications is a bedding
> compound; Moglice or gunstock bedding compound spring to mind.
> Ron Ginger or Smoke should be able to expand on this theme further.
> Ron, Smoke...The floor is yours!!!
> Cheers