Originally Posted by
Mike Holbrook
I believe cauls can be just about any scrap of wood used when clamping. In relation to edge gluing, I think other posters are using cauls to hold the tops of glued boards in line, along the opposite plain the clamps would normally work? I imagine cauls could be made that would help with just about any clamping application though?
I think I made a post asking about Bowclamps, which are just precisely manufactured cauls that have a groove made to accept an F style clamp. One side of the Bowclamps is manufactured with CNC machines to achieve the "perfect" arch for evenly spreading applied pressure to an entire surface. I suppose the question is whether or not the manufactured Bowclamps derive any significant advantage out of the quality wood and precise dimensions?
Bowclamps come in three sizes 24", 36" and 48". I suspect making ones own cauls allows one to come up with greater variety using less expensive scrap or purchased wood? I would be very interested to hear/see details concerning how various posters make and use their variety of cauls?
A problem with any caul is that the curve on the caul needs to take into account the bending characteristics of the wood. And each piece of wood is going to be different. This problem is only real if you want to get the absolute same amount of pressure across the area being clamped with the caul. In the real world, if the curve is not perfect for the wood, you're still going to get a good clamp.
I have a tutorial on my web site on making cauls. One of the things I do in the tutorial is test the cauls after you make them by putting pieces of paper between them and see if you can pull the paper out. This will show that there is pressure all along the caul, but will not indicate that it is the same pressure at all points.
Others have posted techniques for making cauls where you bend the caul wood, then joint it flat while it's bent. This will give you a caul with essentially even pressure all along the caul. I don't remember the technique, but I know some ideas were posted in a thread on SawMill Creek.
If a Bowclamp is cut using a CNC machine, it will likely not produce even pressure along the caul because each piece of wood is different. But it will be close enough to do the job.
Cauls are pretty easy to make and can be made from kiln dried 2 by 4's that you can buy for a couple of dollars each.
And to stick with the main subject of this thread. I use good Baltic birch as a substrate for veneer work occasionally - when MDF will not work as the substrate for one reason or another.
Mike
Last edited by Mike Henderson; 12-05-2014 at 8:22 PM.
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