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I would like to make some of these parallel clamps that use a pipe for the bar.

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Source

The one advantage that commercial parallel clamps have over these is that the clamp faces will always line up; with the Bellevue Woodshop design it is possible to rotate the moving piece so the faces don't line up.

My thought is to glue a small rectangular strip of wood under the pipe along its entire length, and cut a corresponding space (keyhole?) out of the moving part of the clamp. Is this a reasonable solution? Is there another way to prevent the clamp from twisting? Or should I reconsider trying to prevent this twisting?

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    Seeing the ease with which the guy in the video drills through the pipe, it looks like the clamp is made with something like electrical conduit. The greatest benefit of the steel bar in a commercial clamp isn't that it prevents rotation, it's that the bar allows the clamp to exert huge force without deflecting. – Caleb May 25 '15 at 20:03
  • After a glance at the video, I got the impression (I could be totally wrong!) that the movable part of the clamp had screw threads tapped into the locking block. If that's the case, I'd suggest burying a t-nut, so that you aren't relying entirely on fine wood threads. (But please correct my understanding if I've got it wrong.) – Aloysius Defenestrate May 25 '15 at 22:57
  • @Caleb that's true, I was considering all things equal. Would you recommend thicker steel tube? – lars May 25 '15 at 23:29
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    3/4" black iron pipe is fairly rigid and for that reason makes good pipe clamps. – Caleb May 26 '15 at 3:20
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your idea of adding a rib to keep the heads in line has merit and will do what you are wanting. However, my pipe clamps are similar in that the movable part can rotate all the way around the pipe.

Generally once you start tightening things down they don't twist and are not a problem. On top of that as TX Turner pointed out, sometimes not having them parallel is actually a benefit you can take advantage of.

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Nah, I wouldn't bother trying to stop the twist. You can turn the face 180 degrees and use it like an expanding clamp, or a jack. There's a lot of neat things you can do with two jaws that don't have to be parallel. :)

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If the clamp is sitting on a flat surface, it won't twist when you're tightening it down. (And then if it is tight, it won't twist either.)

But to answer your question, you could run 1/4" threaded rod, nutted firmly to the front and the back, and through a free-running hole in the moveable part of the clamp. That won't totally control twist, but I think it's a good start.

Neat clamps, btw. Love the maker spirit.

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