Re: ATM Aluminum instead of ebony star for side bearings

["Michael P. Lindner" <mikel@att.net>]

Bob Prabowo wrote:
> 
> I'm going to use aluminum bar on my side bearings

I experimented with this a little bit (1/8"x1" bar). You don't say if
you're making small (12" or smaller) round bearings or big (ala
obsession) half round ones. The latter is easier due to the large
radius. For small round bearings (mine were 8"), here's my experience.

You will probably want to epoxy the aluminum in place, as well as
screwing down the ends. You will need to form the aluminum first. I did
this by placing it in a vise, with wood on either side to keep the faces
of the vise from scratching the aluminum. Slide out an inch at a time
and bend it gently. You should start with a piece longer than you need,
because the ends will be flat.

I wasn't able to get a diameter of less than about 12" (it just seemed
to always spring back to about that diameter over time). So, you'll need
LOTS of clamps unless your bearing is that large. Cover the face the the
aluminum with tape to protect it from scratches and epoxy, and cover the
faces of the clamps as well, lest you wind up gluing a clamp to the
bearing. Clamp it down well, and make sure there are no gaps between the
wood and aluminum (which will make out-of-round bumps on the bearing).
Then hold down the ends of the aluminum and drill pilot holes for the
screws on the ends. Then take off the aluminum and drill out and
countersink the screw holes. It helps to have a curved piece of wood to
set the aluminum on to drill it (i.e. make a third bearing).

In the end, I found it far easier to use formica for my 8" dob bearings.

One the other hand, my equatorial platform has its sectors wrapped in
aluminum. The radius is 36". I glued it and screwed the ends as above,
but did not prebend the aluminum. Went on just fine.

--
Mike Lindner