I have seen some pretty slick arrangements using small 6000 series ball
bearings on bolts. The tubing in the one case sat corners vertical and four
bolts with bearings supported the tube running horizontally. The bolts were
set at 45 degrees so that the bearings ran on the sides of the tube.
For your vertical arrangement you would need eight bearings to
completely capture the tube post. Sealed bearings that fit on a half inch
bolt don't run much more than five dollars Canadian from a bearing house.
You might get them as cheap as a couple of dollars each.
Randy
"Terry King" wrote in message
.. .
Ok, I'm designing another machine. This is for making
accurate, repeatable cuts on / into large wood beams,
therefore posted to both groups...

I need to build a telescoping vertical elevation section,
much like some Radial Arm Saws have. I want to use standard
steel-supplier square tubing, like 4 to 5 inches, probably
..125 wall or, so. There will be a threaded rod actuator,
possibly based on a trailer jack.

This is a one-off at this point, although I'd like to be
able to document how to make one. IF it works well. So I need
easy-to-get parts. The question:

** What is a good approach to providing bearings for a
sliding, telescoping mechanism with square steel tubing??**

I don't THINK I need antifriction (ball or roller) bearings.
There won't be high-speed or continuous motion.

So, I see something like this:

Two sizes of square steel tubing about 5 inches or so
that telescope with a clearance of, um, .25 inches to .5 inches.
The wall of the outer tube has cutouts of some size and
shape which hold 'things' that reach through and 'bear'
against the inner tube. There probably need to be 'lots'
of these, say 2 per side x 4 = 8 at each 'level' of
contact. Maybe there are only two levels of contact.

What are your thoughts? What is used in existing commercial
designs?

My only thought so far is nylon (other plastic?) bolts in
threaded holes in the outer tube, hex heads inside, jamb
nut on the outside. Adjust for just a little clearance.

Any suggestions or pointers appreciated.
--
Regards, Terry King ...In The Woods In Vermont

The one who Dies With The Most Parts LOSES!! What do you need?