In woodworking Cauls are beams that are used to distribute and direct clamping force over a long length. Generally they are just stout beams that are clamped at the ends. Calling them Cauls officially makes them tools so they don't get thrown out during shop clean up. The downside is that you have to hold and tighten clamps on both sides of the beams and also, you have to have the clamps. These Cauls have built in clamps which make them easier to manage. Three can be made for a lot less than the cost of a single clamp.
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Step 1: Select Beam
The thicker the beam the less it will bend but the heaver in will be. 2-1/2" thickness is a good compromise for Cauls two to three feet long. I am making these beams 28" long, 2-1/2" thick, and 1-3/4" wide. I am clamping 24" wide panels so this is a good size for me. I make three of them so I have one at each end of the panel and one in the middle.You can make three Cauls, 32" long, with a single 8' 2x3
Step 2: Mark and Drill Holes
Marks for hole about 1" for each edge. Drill the bottom pieces with a 5/16" drill bit. Drill the top ones with a 5/8" or 3/4"bit.
Step 3: Cut Threaded Rod
You can get 10' of 3/8 - 16 threaded rod at Home Depot for less than 7 bucks. Use a hack saw to cut to the desired length. I am cutting mine to 12" because I only need a clamp throat distance of about 6". (5" for the Cual thicknesses, 6" for the panel, and an inch to spare.) You can make yours any length you want.
Step 4: Tap Holes
Tap the bottom holes on the bottom pieces with a 3/8 -16 tap. Note that my tap does no go all the way through. That is because I don't have a long tap nor $20 to buy one. Instead I will made a poor mans tap
Step 5: Poor Man's Tap
Use a triangular file to file four groves into the one end of each threaded rod. (It even kinda looks like a tap). They will finish tapping the holes as the rod are installed into the beam.
Step 6: Install Thread Rods
Tighten two, 3/8 - 16 nuts together on the rod near the bottom and use a wrench to install rod into the beam. Remove nuts when done.
Step 7: Apply Packing Tape
Put packing tape on the clamping side of both the top and bottom beams. This will keep them from accidentally getting glued to your work.
Step 8: Assemble
Place top Caul onto screws. They are held and locked down in place with wing nuts and washers. I use Lock Block because they just slip into place and lock down. See the Lock Block Instructable for more information.
Sometime the Cauls will bow with pressure or it may need extra force in a specific place. I use plastic playing cards as shims. A pack of cards is cheap. A pack missing a card is free.