Sliding metal parts

[Andy Mac]

Hi there,
I'm faced with a problem of how to get some square stainless steel tubing to telescope, and I think have come up with a reasonably foolproof way... which I'll now share!:rolleyes: There is steel tubing available in standard telescoping dimensions, but I couldn't get stainless, and anyway, metal-on-metal is not the best for friction and wear (or noise for that matter).
This assembly is one of 2, for a pair of funky lecturns I designed. The outside tube is 50 x 50mm x 1.2mm wall, the inside is 38 x 38mm x 1.2mm wall, so a fair bit of slop!
The first photo shows one end of the smaller tube, where I've had pads of 3.5mm stainless welded all around. I then drilled blind holes into these pads to accept some wear "buttons": 1 on two opposing faces to simply take up lateral movement in that axis; and 2 on the remaining opposing faces, which will not only take out lateral movement, but also twisting moment of the lecturn top.
The secret wear button inserts will be revealed next post!

[Andy Mac]

Righto, now the fun bit. The holes I drilled in the pads are 1/4", so I decided to mix woodworking tools with metalwork, and dragged out the 1/4" plug cutting bit. Its one of an excellent 3 piece set from Lee Valley, bought through Carba-tec.:) The plugs come out slightly tapered, mainly for a snug fit, but also allows for variation in drill bits and timber characteristics.
The material I'm using for the wear buttons is salvaged from a scrap yard, leftover slabs of a Teflon-like material, an industrial nylon often made into bushings and slides. I've used it for all sorts, including bearings on a small windmill...maintenance free, bulletproof stuff.
So here's a shot drilling a bank of inserts with the plug-cutter. Drills easily, then bandsawed into strips before cutting out each insert with a Stanley knife.

Cheers,

[Andy Mac]

Once each plug is free I hammered them into the blind holes, and they stayed hit! I trimmed the excess with Stanley knife, before getting more accurate with a file. See photo, sorry its a touch out of focus:o. Due to the greasy feel of this stuff, filing is a tad slow, but at least I didn't file too much at once. I dressed all sides, with several trial fits, then voila! in it slid...nice and even, with next to no backlash! I can tune the fit by filing more or less, or even replace the insert if I stuffed up. :D
I am quite happy with such a simple fix, but I wish I'd though of it before I welded similar stainless pads inside the neck of the 50mm outer tube. I could have drilled them prior to fitment, ready to take these little wear pads.:mad: I'll just have to rely on the inner tube to take up the slop.
I hope this idea will be of some use when you consider the sliding of metal parts, I think it has loads of applications!:)

Cheers,

[jmk89]

May I ask why you didn't just attach rectangles of the teflon stuff across the whole width of the top of the inner leg (I would make them about 50mm deep to provide some summort). You could attach them with csk screws running into threads tapped into the inner leg steel. I would countesink the screw heads by 1 or two mm to allow you to work on the fit using a file.

I would have thought that this would be easier and more stable in the long run.

[Andy Mac]

Hi JMK,
Fair call, except for the thin wall not really allowing much tapping depth, and I can't put any nut or protruding thread on the inside of the smaller tube. I need all the space I have for 1/ gas strut to lift the lecturn top, and 2/ remaining gaps for plumbing of electrical gear (ie. light, mike, AV etc).

Cheers,

[JDarvall]

Great idea Andy. Ta. Something to keep in mind.

I've got those tapered plug cutters as well. Clever things eh. What do you think of them with wood ?

I've noticed sometimes when plugging a hole the air pressure buildup of the plug being forced into the hole causes a unsightly gap at some point, where the air wants to escape.....have you noticed that with some timbers.

Makes me feel its better to not use glue with them sometimes, since the glue just adds to the pressure...probably don't need glue a lot of the time anyway.