telescoping square steel pieces

Apparently my ISP is having trouble with its newsgroup servers. Anyway, I posted this some time back and it never made it so I'm reposting it, maybe this time it will. - GWE
I'm constructing a gantry which has height-adjustable legs made from telescoping square steel tubing. The problem of how to make square steel tube slide inside another without binding or rattling excessively has been around for a long time, and this was my approach to deal with it. There are two square steel tubes in question - the outer one and the inner. The outer tube is 4x4x.180" tube, and the inner is 3-1/2x3-1/2x.180" tube. If you do a little arithmetic, you see that the inner dimension of the outer tube is 3.64" which leaves .140" of slop. Also, the outer tube has a weld seam down the center of one side, which seems to be about .060" tall.
My approach was to cut sheet metal shims to fit the inside flats of the tube. On the weld seam side I used two shims which go on either side of the weld. The inner tube slides against these shims, not against the weld.
For my parts I used 13 ga. sheet metal, not because it was optimal but because it was what was available. This leaves a gap of about .05" which isn't optimal but it's a whole lot better than .140"! If I'd had 16 ga. I would have used shims on both sides.
I drilled the outer tubes 5/16" then deburred the inside of the holes. Then I clamped the shims inside and plug welded them from the outside. The picture shows the shims inside the tube. If you look carefully you can see the heat affected zone below the plug welds.
This was admittedly a little tedious, but it worked well. I used an internal countersink tool from Noga in conjunction with a file to do the deburring.
The picture is Next problem is how to paint the inside of the tubes, the longest of which are about 30".
GWE

Apparently my ISP is having trouble with its newsgroup servers. Anyway, I posted this some time back and it never made it so I'm reposting it, maybe this time it will. - GWE
I'm constructing a gantry which has height-adjustable legs made from telescoping square steel tubing. The problem of how to make square steel tube slide inside another without binding or rattling excessively has been around for a long time, and this was my approach to deal with it. There are two square steel tubes in question - the outer one and the inner. The outer tube is 4x4x.180" tube, and the inner is 3-1/2x3-1/2x.180" tube. If you do a little arithmetic, you see that the inner dimension of the outer tube is 3.64" which leaves .140" of slop. Also, the outer tube has a weld seam down the center of one side, which seems to be about .060" tall.
My approach was to cut sheet metal shims to fit the inside flats of the tube. On the weld seam side I used two shims which go on either side of the weld. The inner tube slides against these shims, not against the weld.
For my parts I used 13 ga. sheet metal, not because it was optimal but because it was what was available. This leaves a gap of about .05" which isn't optimal but it's a whole lot better than .140"! If I'd had 16 ga. I would have used shims on both sides.
I drilled the outer tubes 5/16" then deburred the inside of the holes. Then I clamped the shims inside and plug welded them from the outside. The picture shows the shims inside the tube. If you look carefully you can see the heat affected zone below the plug welds.
This was admittedly a little tedious, but it worked well. I used an internal countersink tool from Noga in conjunction with a file to do the deburring.
The picture is Next problem is how to paint the inside of the tubes, the longest of which are about 30".
GWE

In cases I've seen, tubing is used that allows a somewhat larger gap like .25" all around and bearing plates of nylon are placed inside the outer tube end to bear on the inner tube. The bearing plates are fastened with nylon bolts so as they wear the bolts can as well.
Pete C.

WHAT!? Do I have to write all that nonsense again? Did you try ?
Nick

OK, I'll try to find some different nonsense. :-)
Nick

Nick, this is *different*. Last time I was asking how to do it, this time I'm telling how I did it along with pictures. I am pretty good with google.
GWE

Why didn't you put the shims on the outside of the inner tube? It would have been easier than plug welding them. As for painting the insides of the tube., seal one end with a cap or plug, pour some paint inside, seal the open end and slowly tilt the tube back and forth and turn it around its length. That will put a coat of paint on the inside. After you get through agitating the tube, pour the excess paint out.
Jim Chandler

The inner tube is 30" long - the outer tube is roughly eight feet long. I would have had to buy a whole sheet of sheet metal to do that, would have cost a bundle. The way I did it I could use scrounged material - free.
I had thought about dipping/draining. I think I might try that. In the past when I've dipped parts the paint has formed large drips. Maybe if I thin the paint first ..
GWE

Nice job! Maybe I would have done it with a little more brute force. Bore for plug welding, slam in the strips and the inner tube (no deburring) and then plug weld. I bet that the welding would have melted down the burr and pulled the strips a bit to the outer tube.
This does *not* mean that you made a bad job!
Painting inside: I would get a 50mm foam roller and build my own loooong handle for it. Don't dip it in paint. I doubt that the paint will stay on the strips and I think you'll have more friction.
Nick