Bowed Cauls - Shop Made

glenn bradley

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You are probably familiar with the idea of bowed cauls. They allow you to place even pressure across a carcass surface where you would not ordinarily be able to get a clamp for glue ups. I made a couple 24" ones awhile back and find them useful for many things including the most touted benefit; reducing the number of clamps required to do a job.

All that aside, I needed a couple more with a little more oomph so I thought I would share the process. I use some scrap material about as long as the caul will be. Make a mark to use as a reference for the midpoint of the caul's length. I use a shop made fairing stick to select my curve, draw a line from the mid point of the desired caul length to where the stop block will be. Sand to the line to create a template that is slightly more than half of your caul's length.

I attach a support block for the rear edge and a stop block to register one end. The rear support is set back from the edge of the template the distance that will translate into your caul's height at the midpoint.

The curve runs from what will be the midpoint of your caul length to the stop block position and beyond to allow a smooth transition of the pattern bit. Rough cut the caul blank to width but cut it precisely to length.

caul 00a.jpg

Run the template from a little more than the halfway mark through one end of the caul to cut half the curve. Flip the blank and repeat for the other end.

caul 00b.jpg

On these two I wanted about 1/8" of rise at each end over 24". The clamp is just snug enough to hold the caul still for the photo.

caul 00c.jpg

Sorry for my photographic skillset (or lack thereof), you can sort of see the gaps at each end in the pic on the left and then I give each clamp a couple turns in the pic on the right. Surprisingly little clamping effort is required to bring it down tight and it really spreads the pressure out nicely.

caul 00e.jpgcaul 00d.jpg
 
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Thanks Glenn! I was actually planning on asking the question "How do you make bowed cauls" within the next couple of days. Seriously. :thumb::thumb::thumb:
 
I have seen other methods like bending the blank in some sort of carrier and running it through the table saw as a rip cut. When the tension is released the bow presents itself in the relaxed blank. I went low-tech.
 
I think I saw something one time about using a jointer to do it as well, something about lowering the outfeed table and keeping all pressure on the outfeed side. Your method just looks much more straightforward.

What I'm looking forward to is using a set of cauls during the glue up phase on a table top to keep things flat.
 
I have a new way of making curved cauls.

1. Make the blank for the caul then rip about 1" off the edge.
2. Select a flat board longer than the caul add a stop to the front edge. (to be used as a sled for the planer)
3. With double back tape fasten a 1/4" to 1/2" thick spacer at each end of the flat board that the strip from the caul will rest on. I also use double back tape to hold this strip to the spacer.
4. Run this assembly thru your planer (take off small amounts) and the pressure from the hold down rollers will deflect the center of the caul strip and material will not be removed from the center only from the ends.
5. Once you have the curve amount you are happy with glue this strip back on the rest of the caul and you will have a curved caul based on the deflection of the actual material.

I actually do 2 to 4 at a time depending on how many I need.
 
Do you think poplar would work, is it too soft?

I've got a bunch of 8/4 maple coming (The shipper just called, he is still planning on sending the truck tonight :rolleyes: ) so I'll probably use some of that. I'm sure I'll have some offcuts to use.
 
I used some 'freeway' maple, so named because LOML picked up a bunch off the side of the freeway on the way to work. If I were to need to buy some good hard rock maple, I'd save the money and time and just order them from Bowclamp ;-)
 
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I purchase some straight grain fir 2x4's. 48" fits a lot of panels so I cut an 8' in half to make two cauls. Around here, a fir 2x4 is about $3.

The only disadvantage is that you may have to let the 2x4 dry out for a while before you can use it.

Mike
 
Thanks very much Glenn. I wish i had asked this question some time back. I ended up settling for "cauls" (if you can call them that when they have no bends) that were straight cause at the time i could not figure out how i would get a decent edge on the curve and more important what curve to go for.

Just to be real honest in my mind I had visions of a good bow. :rofl::rofl: Boy i would have needed serious clamps to bend my cauls down to be useful. :D So i settled for flat now i will add this to the jig list of to do's.

Oh boy that list is getting longer and longer.:)
 
The Borg by me finally started carrying some Kiln Dryed. Fortunately, I've got a stash of 2x4. For some reason, I usually pick up a few everynow and then and I've got a stash of them that have been drying for some time.

So Pine Curved Cauls it will be!
 
BTW, this is not as good as what Glenn posted, but the woodworking school I've been attending (Cerritos College) teaches people to make cauls by jointing them, then taking a few swipes with a hand plane. You take one swipe from the center, then one from closer to the end, then another even closer to the end, etc.

Not as precise as what Glenn posted but it works. Probably the way our ancestors did it.

Mike
 
Hmmm, And that hand method kind of appeals to me since I've been starting to 'collect' a few planes lately.
 
Great to see. I think you'll find that the more accurately you can make them... the more usefull they become. Opens up tons of possibilities...Edge-banding, veneer press, marquetry, panel glue-ups etc. Give 'em a good coat of wax to keep from gluing them to your work-piece.:thumb:

And let's see some action shots.
 
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