crowned cauls,best way to make,use them?
kenney66
| Posted in General Discussion on
i am gluing up some 3/4 oak boards and i am having a slight diffuculty making all the boards line up perfectly. I have jointed all of the ends of the boards so there is no gap. I did a dry fit and use clamps and straight cauls but the fit was not perfect. I was thinking that I should use crowned cauls. What is the best way to make crowned cauls. Table saw? Maybe the jointer? The cauls i am using are 4 feet long. Where would the tapers start? How big would the taper be? Also, should i expect the boards to not line up perfectly and be prepared to clean it up after the glue dries? Would bisquits be another good alternative?
Replies
One way to glue up a table top is to do it one board at a time. That way you can use carpenters clamps to reach the glue joint to align the two boards.
Hi Kenny. I lay my clamps on my assembly bench in there upright position ready for use. Beside each one I have some maple 'cauls' that are about 3/8" taller than the bar of the clamp. The wood that I am clamping lays on the 'cauls' and not on the clamps. I gently snug up the clamps to close the gaps between the boards and then tap the boards into alignment with a hammer. If one board is a little high, where you may think that a biscuit would bring it into alignment, just tap it with a hammer to bring it down. The 'cauls' under the boards but higher than the clamp bars stops the bowing effect of the clamp being tightened. Hope this helps Peter
kenney66
There is no "rule of thumb" but I would probably have a curve resulting in a 1/16" clearance at each end for a caul 24" long to a 1/8" clearance for a caul 36 - 48" long.
You want to use a wood that will bend easily so I would suggest using as clear and straight grained as I could pull from the pile DF or Pine 2x3s (2x6 ripped in half).
I would start off by cutting my caul stock to length, use a floppy straight edge to mark out the ellipse and then use a bench sander (belt or disk). Sand away the stock with 60 - 120 grit and then glue on cork strips.
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Michael in San Jose
"In all affairs it's a healthy thing now and then to hang a question mark on the things you have long taken for granted." Bertrand Russell
Been using curved cauls over 30 and no biscuits and get perfect alignment. Have glued up 4' x 10' panels and table tops singlehanded with no problems. No real rule of thumb on how you make them but having them all the same is critical in my experience. I've put an 1/8" crown on 1-1/2" wide x 2" tall and 48" long cauls. I've used a pattern cutting bit to trace off my master caul. I just put plastic over them to keep glue from sticking. I've never found any need for cork on the cauls.
If anyone wants to get anal about cauls our British brethren, Ian Kirby did quite a lot of study a couple (yikes, was it three?) decades ago and determined that a 36" caul should have an even radius of twenty six feet. He was hawking torsion box construction and this was the number he came up with for exerting even pressure when clamped tightly.
Lee
Hi Lee,
You wrote: " and determined that a 36" caul should have an even radius of twenty six feet..."
Would you happen to know what that works out to (e.g., 1/16th" per 3" of caul length)?
I put a radius on my cauls by, after having jointed the to-be-caul straight and square, taking my jointer plane and take succesive "swipes" at it, starting from just off the middle of the caul, every inch or so, so that my first swipe is (middle + 1" then off to the end of the board), the second swipe is (middle +2" then off to the end of the board, etc.) I hope you know what I am trying to describe??? To increase the caul's radius, one can either reduce the distance between stroke starting points or, obviously, increase the shaving thickness. Since you aren't using the cauls to spread out clamping pressure on the glued edges, then all you need to be concerned about is making the pressure not so great as to crush wood fibers of your project's material, but great enough to keep the boards flat across their width ... seems like 1/6th" every 7" to 8" ought to suffice(?).
Fwiw- I use regular ol' 2x4 pine (without knots on the "material contact" edge) on edge for my cauls. I cut notches on their ends to *hold* bar clamps in position. Since I am using softwood (pine), and there is plenty of surface area (2x4), I don't ever seem to have a problem with crushing wood fibers.
Btw- Lee G. I love your website and your work ... what wonderful carving capabilities and fabulous aesthetic (artistic) sensibilities. Awesome. :-)
-Peter T.
Wow, you really know how to ask! Thanks for those kind words.First, if what you're using is working for you then by all means continue. I'm not a purist or an absolutist, skinning cats can take many forms and yours is as valid as Kirby's. He'd probably not admit to that but the reason his information stuck in my mind is that he and I had a bit of a row back then concerning a different topic. I have great respect for Ian Kirby but he can be a bit of an a$$, at least 20 years ago he could.So, I went out, found my big boy's tape and struck a line at a 26' radius. A radius does not diminish steadily toward a chord as they near each other. That's geometry and if you want to get into that draw a radius, draw a chord and see for yourself. I'm certain someone versed in math could give you the formulae but it's not me.Here's what I measured...at 18", the midpoint, the rise was 1/2". 7/16" at 12"..., 3/8" at 9"..., 1/4" at 6". I'll leave it to you to extrapolate more points.Another trick commonly used is to rip a bunch of strips of Homosote, I can't remember the Western name for it right now, it's a felt product that's 1/2" thick that will take up the slack of inprecise cauls. It works pretty well.Lee
Edited 2/7/2005 6:42 pm ET by Lee_Grindinger
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