The Roubo-Style Panel Clamp

This was going to be my year for getting enough clamps: I was to troll the tool sales and estate sales to get what I’ve been lacking. Then you-know-what came around, and that plan whimpered and died. As fate would have it, I’ve got an upcoming project that requires more clamps than I have.

Perhaps I was fortunate that I was reading the Roubo translation from LAP recently, and of course Roubo talked all about clamps. He described a panel clamp made from two boards that he called “twins.” He said that “the use of these tools is excellent,” and his recommendations are not to be taken lightly. OK, whatever, it looked reasonable, so I wondered if anyone in the 21st century had made them. I should have guessed that Don Williams had done it; here’s his blog post. There’s a snippet of the Roubo plate in there. Also, keep in mind that even though we’re calling them “Roubo clamps,” we don’t really know how the form evolved over the years to the form he described.

The construction of these is simple enough that it was definitely worth trying. I grabbed some southern yellow pine 2x4s and put a bunch of holes in:

Hand tool disclaimer: I used my drill press. Sure, I could have used my brace, but it would have taken a lot longer, and this is one thing that a machine actually does really well.

The holes are alternately offset like Williams did. It seemed like a good idea at the time. He used a mortising machine to make 1/2″ square holes. I planned for 3/4″ pegs, and I didn’t like the idea of using round pegs, so I needed to square up the holes. With no mortising machine of my own, I just went at it with the biggest mortise chisel that I own:

Thankfully, these don’t need to be appearance-grade. And yes, I chopped halfway in from each side, and yes, there’s something underneath the wood to keep from putting (any more) nicks into my bench.

This was something of a chore, but not awful. After that, it was simply a matter of resawing, making the pegs and wedges, and before long, I had three twins:

I tested them on some boards that were lying around:

These seem to work well. I pounded the wedges in pretty hard. Using them requires some acclimation, so I guess another reason to use liquid hide glue is so that you have enough time to put them on. Although I’m using double wedges here, I might change to single ones for the simplicity.

Being southern yellow pine, I think they’ll be strong enough. Roubo describes beefier things: roughly 4-5 inches wide, and 2 inches thick (but is this per side or for both twins?). His described mortises and pegs are 1.5 inches wide–four times the volume profile. But from what kind of wood would he have seen these made? Oak would be very strong for the pegs, but its tendency to split cleanly might be something of a concern for the twins. Beech wouldn’t have that kind of problem. Or what if it were a wimpy sort of thing?

Oh well, I don’t think that’s something I need to concern myself with that until I manage to break these.

4 thoughts on “The Roubo-Style Panel Clamp

  1. I’ve a question/comment on the use of the wedge(s). If you simplify by using only a single wedge, would you then want the pegs (and peg mortises) to be slightly angled to match the angle of the wedge? Otherwise the corner of a peg might wear a groove into the edge of the wedge.

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    • That’s a good question; I’ve also thought about that. Roubo didn’t mention anything about it. I’ve decided not to care until it manifests as an actual problem. Wedges are cheap and quick to make. Regarding the mortise, there’s no point in changing that profile. Only the side opposing the wedge sees any registration against the peg.

      There is another double-wedge configuration possibility with asymmetrical wedges. The one against the peg could be smaller and have a hook to catch the side of the peg, so that you only really have to bang on one side to tighten everything up. This would be easy to make, and in theory, not really any more complicated, so it might be worthwhile.

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  2. I looked I building the same clamps for a while but was wondering about glue squeeze out and the risk that the clamp would be glued onto the panel. Did that ever occured to you?

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