Not actually in use but, this demonstrates what happens. The first pic shows the curved side down and only the center contact point in applying pressure.
caul 00e.jpg
If the bench top was a long area to be clamped that you could not normally reach with typical clamps, tightening the clamps creates a line of pressure along the caul.
caul 00d.jpg
I'll see if I can sind a shot of them in use on a carcass.
"A hen is only an egg's way of making another egg".
– Samuel Butler
Contributor
Yeah I don't understand, it applies pressure at one point but why not use a flat clamp block and apply pressure across the whole surface?
WoodsShop
Because the flat block will apply pressure at the clamp points and then less pressure as the block surface is farther from the clamping point. The bow in the caul makes up for this by applying pressure somewhat equally over the entire length. At least, that's the theory; works in practice for me.
Ah, found one. You can see the caul at the top center. I am using one clamp at each end to clamp the 24" length of the panel to divider dado joint.
TS-Outfeed (22).jpg
Last edited by glenn bradley; 12-17-2017 at 11:08 AM.
"A hen is only an egg's way of making another egg".
– Samuel Butler
Contributor
That makes sense! You'd need a flexible piece of wood not too thick?
WoodsShop
Contributor
What I do is use ipe clamp blocks that hopefully don't bend much. I need to look into these curved cauls :-)
Trial and error about getting the curve just right?
WoodsShop
Contributor
Is this another version of Bow Clamp?
Bowclamp.jpg
Depends on the material. On this Pecan set I use 1/8" on the 24", 1/4" on the 36" and 3/8" on the 48". I believe the commercial ones made of maple use a more pronounced curve.Originally Posted by Joe Wood
cauls-v2.jpg
I just sand them smooth and apply wax. I re-wax about once a year.
"A hen is only an egg's way of making another egg".
– Samuel Butler
Moderator
Yes...this thread is about "rolling your own"...cutting the curve.
Glenn's explanation is spot on...the "bow clamp" (commercial or home-made) distributes pressure across a long space with only two clamps required; one at each end. This is very convenience for wider glue-ups where the wood has it's own ideas and doesn't want to stay level at the individual joints across the workpiece. The commercial version that I own have a cross section of about 2+" x 2+", give or take and are made from hardwood. You don't need or want something "super flexible" because you want the clamping action to do the work and you always want them to spring back completely when the clamps are released.
--
The most expensive tool is the one you buy "cheaply" and often...
Member
Two opposing curves create a flat plane under compression
20171212_213354.jpg20171212_213530.jpg
These are 2.5" at the center, made out of 2x framing material 48" in length. The curve is about 3/8 per side or 3/4 for the opposing pair. It's enough pressure I'm tearing the threads up on those bessey clamps
Last edited by Jared Sankovich; 12-17-2017 at 1:02 PM.
Member
Yes, but I think curved cauls were around long before the "bow clamp" existed.
Contributor
Oh I understand now, you need an opposing curved caul underneath?
WoodsShop
Member
Yes.
In my experience, unless you have a significantly thicker (in cross section) bottom caul it will bend.
Contributor
The bowclamp has some features that a shop made caul might not have, but the cost is much higher. I made my cauls from kiln dried 2 by 4's which were a couple of dollars each and I was able to get two 4' cauls out of an 8' 2 by 4. So a set of 4' cauls (two cauls) was a bit less than $3 for me - plus some time to make them. Two 4' Bow Clamps are listed for $95 (plus $20 shipping).
Mike
Go into the world and do well. But more importantly, go into the world and do good.
Contributor
"In my experience, unless you have a significantly thicker (in cross section) bottom caul it will bend."
Jared don't you want the cauls to bend??
WoodsShop
Member
That's kind of the point, isn't it?
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