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Super-Slick PTFE Tape for linear bearings

Posted by Joshua Merchant 
Super-Slick PTFE Tape for linear bearings
September 09, 2008 12:07PM
There seems to be a bit of a interest in linear sliding mechanisms lately (e.g. the posts in the builder's blog and Viktor's post on this forum). Sort of related is something I've used for my plywood McWire.
[Skip these next two paragraphs if you don't care about my RepStrap's use of the idea.]

The basic McWire design has, on each stage, 4 of 1/4" thick strips of PTFE (1 in each corner). Under each stage are two parallel aluminum U channels, each of which has two of the PTFE strips resting on it. Movement is along the length of the channels. To keep the stage in line on the channels, it uses spring loaded bearings pressing against the stage. See the doc if you aren't familiar with the design. [reprap.org]

What I found is that it is much cheaper to use an arbitrary building material (in my case, plywood, but I will eventually switch out the wood pieces with RepRapped plastic pieces), and apply Super-Slick PTFE tape (that's what it's called, McMaster # 6305A12) instead of using PTFE strips and aluminum channel. Instead of 1/4" thick PTFE strips, I used 1/4" thick plywood cut into rectangles, and applied the tape to one side. For each aluminum channel, I cut one length of 1/4" thick plywood and one length of 1/2" plywood, glued them together (it needed to be 3/4" thick and I only had 1/4" and 1/2" plywood), then applied the tape to the top. The tape on the small rectangles slides extremely well on the tape on the longer (channel) pieces.

So anyway, adhesive on the tape is an acrylic adhesive (though it is available with a silicone adhesive, search McMaster with that part number and it pulls up the page with the various options), so I think it's possible to apply the tape to just about any two surfaces we want to slip/slide past one another. Specifically, I'm thinking about using it on RepRapped plastic pieces, which it should adhere quite well to.

Viktor made a comment in his thread about his stuff not being very RepRappable. What I'm thinking about is a sort of mostly-RP linear stabilizer, the only non-RP part of which is the tape (which is pretty cheap because it's so thin). I think there are a few options for this, but I won't say much about them because I haven't put much thought into it (and I'm really only writing this post in case the tape happens to be useful to someone).

I suppose it may be possible to have a cylindrical linear bearing, which would basically be a hole in a RepRapped part which has PTFE tape lining the interior walls. I think this would be difficult to implement, but it might be easier to have two halves of a hole, separately lined with the tape, which are brought together to form the hole and bearing.
Perhaps it would be better to have a square hole, with one corner pointing down and one up, etc (rotated about it's axis 45
Re: Super-Slick PTFE Tape for linear bearings
September 09, 2008 01:03PM
I like the idea of teflon tape. I wonder if you could use teflon plumber's tape? I have some of that! It's not sticky though. So I guess the question becomes "is the friction low enough that I can tape the teflon tape at either end (folding it around the top of the stage) instead?"

I'll have to add that to my list of things to try.

I'm building it with Baling Wire
Re: Super-Slick PTFE Tape for linear bearings
September 09, 2008 02:37PM
Hi John,

... we already had some talk about using PTFE-tapes and PTFE-coated glass-fabrics against bulk PTFE-stripes and -blocks.

I used milled blocks of PTFE and -coated material for heavy-load-sliding in microassembly and microscopy.

Both works good when in a clean and dustfree area - but when you let it settle over time, then the thin PTFE-coated sheets have a backdraft: they are harder then the bulks and accumulated abrasive particles from the 'normal' dust grind the gliding surface, so they tend to destroy the moving pads over time (look at the surface of your mousepad and/or the table beneath).

The bulk blocks are softer, so hard dust-particles didn`t stick out but 'dive' into the PTFE, so it's not so abrasive.

I didn't think plumbers tape is feasible - it's not rigid enough to stay long and you can't glue it in a perfect plane surface.

So the conclusion: - when using PTFE-coated sheets (like the gliding-pads atached to the bottom of a PC-mouse) you should regularly clean the moving surfaces and cover your mechanic when pausing to protect from dust ...

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