Replies

1. 
   RickL | Aug 22, 2006 02:19am | #1

   I usually put an 1/8" of crown on a 36" to 48" hardwwod caul. Whatever works is the rule of thumb.

   http://www.taunton.com/finewoodworking/Community/QADetail.aspx?id=26546

2. 
   ring | Aug 22, 2006 08:12am | #2

   Obviously this isn't rocket science and whatever works for you is good.  I wouldn't rip them into 2 pieces though.  The cauls I use are about 1 1/4" x  2" and I wouldn't want them weaker.  I'd say that anywhere from 1/8" to 1/4" of camber is OK for these.

   BTW, I have 2 sets:  one for glueing panels as you describe, another with reverse camber for gluing faceframes.  When attaching face frames to cabinets I want to use one clamp to apply pressure over a 2' length of frame.  The cauls with a "concave" edge allow me to put one clamp in the middle and spread the pressure nicely over the frame piece.

   DR

3. 
   THintz | Aug 22, 2006 09:39am | #3

   I make my cauls flat but stiff as all they do is hold the boards flat while clamps add the pressure on the joints, which I also have learned (the hard way) to minimize. If the boards are jointed, very little pressure is needed anyway.

   see the link below for photos and info on how I make the cauls, which have worked very well.

    

   http://www.newwoodworker.com/cauls.html

   Tom Hintz

   Because there is always more to learn!

4. 
   Michael | Aug 22, 2006 05:29pm | #4

   as others have commented, leave em full width. You may need that strength at some point and having one break at a critical time would be disappointing.

   I coat my clamps and cauls w/ a dissolved parrafin in MS solution (spritzer bottle, let the solution harden and buff very hard).  Only have to do this once.

   Cheers,

   Michael

   Michael

1. 
   jjohn83 | Aug 22, 2006 05:54pm | #5

   Thanks to everyone.  Lot's of good information here.

2. 
   forestgirl | Aug 22, 2006 06:16pm | #6

   "I coat my clamps and cauls w/ a dissolved parrafin in MS solution...."  This is new to me, could you expand?  Proportions, how you make it?  Thanks.forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-) 

1. 
   Michael | Aug 22, 2006 07:28pm | #7

   Hi Forestgirl,

   I don't remember where I first learned this, so I apologize if credit is due to someone on this board.

   Basically, you dissolve as much shaved wax as you can in a mineral spirits solution.  You can either let it sit on a shelf and the MS will dissolve the wax over time, but it's very slow.  You can greatly accelerate the dissolving time by applying heat, BUT, be sure you don't use any open flames (I realize that this should be obvious, but I've heard of it happening).  The easiest way is to boil some water on the stove, then pour it into a double boiler bottom and place the wax / MS mix in the top pan. 

   Once dissolved, the wax remains suspended if the product is sealed. 

   You have to be cautious when choosing a container for spraying the MS / Wax mix since MS can dissolve some of the cheaper plastic sprayers.  There are some household chemicals that have robust spray bottles though.  When the MS evaporates the wax remains as a thin coating / residue.  It's dang near water proof / oil / finish proof and is very easy to manage.  Most go with paste wax, but I prefer the ease of spraying this solution on.  I can spray all my clamps down in a minute or two and the coating lasts for years.

   One reference to a slight derivative (has varnish also) I linked below.

   http://www.hammerzone.com/archives/exterior/finishes/water_repel.htm

   Not sure how well I wrote that up, but hopefully it explains it okay.

   Cheers,Michael

1. 
   forestgirl | Aug 22, 2006 09:55pm | #8

   That is just too cool.  Thanks, Michael.  I'd think an electric burner at the lowest setting would be safe?? at least as long as the human operator doesn't spill stuff, LOL.forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-) 

1. 
   Michael | Aug 22, 2006 09:59pm | #9

   You're quite welcome :)  Although, I can't take credit as I mentioned, just passing along anothers good idea.

   As to the electric burner, it might work.  Just keep it low and then just keep adding wax shavings until they stop dissolving :)Michael

3. 
   alias | Sep 01, 2006 12:56am | #11

   hello michael- i'm having a little trouble with the curved caul . my minds eye would tell me that the center ( or high point of the curved caul) would the starve the center of the the glue joint. before the ends . because the uneven pressure exerted on the panel . am i missing th boat on this one?? i'm by no stretch a newbie i do restoration carpentry for a living .
   also what are the advantage to the caul , as oppossed to a 2.5 x 2.5 piece of hardwood?/ thank you for any help.." Crea la mitad de lo que usted ve, y nada de lo que usted oye."

1. 
   HowardAcheson | Sep 01, 2006 05:45am | #13

   From a practical point of view, it's impossible to starve a wood joint with the clamps used in the amateur shop. Joints require 200 psi for hardwoods. A 3/4 black iron pipe clamp can exert about 1000 psi. So a 24" glue joint with 3/4" stock needs 3600 pounds of force. Two pipe clamps fully tightened(one on each end of the caul)will only produce 2000 pounds. So starving a joint is not something to worry about. The tigher the clamping, the stronger the joint.Howie.........

1. 
   alias | Sep 01, 2006 05:52am | #14

   thank you , for your time ....." Crea la mitad de lo que usted ve, y nada de lo que usted oye."

2. 
   Michael | Sep 01, 2006 05:58am | #15

   Actually, the slight curve works in favor of spreading out the pressure that is placed on the outside edges by the clamps.  The slight bow will straighten out as pressure is applied to the outside edges.  Visualize a thin, flexible piece of wood that you center on a pipe.  If you grab only the outside edges, this will cause it to bend in the middle correct?  Now, thicken the piece up and add a curve to the bottom.  In order to bend it as we did in the first instance it will require more force in the center, gradually causing the curve to disappear and the force comes into contact all along the bottom of the caul.  (I'm not sure I explained it all that well).  

   The entire intent of a caul of course is to evenly spread pressure across the piece being clamped.  I only used curved cauls when I do clamping across a box or panel myself. 

   I use straight cauls to assist with edge banding and other items which I can access the entire length with clamps.

   I hope that helped some.  I couldn't locate a good picture of the physics behind the principle. 

   Michael

    

5. 
   HowardAcheson | Aug 31, 2006 01:17am | #10

   I don't get fancy with cauls. I use KD12 construction 2x4's. I joint one narrow edge flat then use a hand plane to create a slight convex shape. Start at a point about 25% from one end and take 2-3 strokes with a plane to the end. Then move to the middle and take 2-3 strokes continuous from the center of the board to the end. Turn the board and do the same to the other end. That is enough slope for a 24-36" caul. It's not rocket science. I don't even bother to finish them. Sometimes I don't even keep them. They only take a couple of minutes to make if I need new.

   Howie.........
6. 
   craig | Sep 01, 2006 05:41am | #12

   I rip down a 2x6 in half and joint one edge.  I use packing tape on the jointed edge so it doesn't stick to the wood or glue.  Using 2x3's 2-3' long works fine for me.  If I need extra pressure in the middle, I just double or triple the packing tape where I need it.