Corner clamps (also known as mitre clamps, angle clamps and various other variations on a theme) are really useful where you have a large structure that is difficult to keep square while under construction. One of the best things about these clamps is they cost almost nothing to make, the total cost of the pair of clamps I made was probably less than a pound.
This project along with loads of others is also available on Wobblycogs Workshop.
- 2 * 50x50mm @ 300mm PAR timber or similar
- 1 * 250mm 12mm Hardwood ply
- 3 * 4x40mm wood screws
- Wood glue
- Mitre saw
- Plane (optional)
- Speed square
Step 1: Prepare the Arms
At the mitre saw cut a couple of pieces of 50x50mm PAR timber approximately 300mm in length to form the arms of the clamps. The exact length doesn't matter but a little under 300mm is a good choice as things are often built in 300mm increments so the clamps will fit more places.
Use a straight edge to find the flattest face of one piece and mark it. This will be on the outside at the end of the construction. Find the best matching face on the other piece and mark that.
Step 2: Join the Arms With a Half Lap
Mark up for a half lap joint and then set up the mitre saw for trench cutting. Cut a few trenches across each joint and then clean up the joint with a plane and chisels. You aren't aiming for perfection here just to produce a fairly flat surface for gluing later. When you are happy with the joint drill, countersink and screw it together.
Step 3: Add the Brace
Cut a strip of 12mm hardwood ply about 50mm wide and 250mm to 300mm long. With some care this can be done on the mitre saw although if you use a small scrap as I did take care with the set up. Lay the brace on the arms and screw one side down. Using a speed square or other means to find 45 degrees adjust the angle of the brace and then clamp it into position at the free end. Drill through the brace and arm at the clamped end and add a screw.
Step 4: Glue Up
Take the clamp to pieces and apply a liberal coating of glue to all meeting surfaces. Screw everything back together and clean up any glue squeeze out.
Step 5: True Up and Check for Square
Cut the over hanging corners off the bracing off and then put the clamp back on the mitre saw. Put the best face against the fence and then trim a small amount off the other face. If you have worked accurately you will find that you only need to trim 1mm or less.
Flip the clamp over and place the freshly cut face against the fence and trim the other face. Take care with this step as the brace will be against the bed of the saw and the piece won't be as stable as it could be.
Trim the corner off the clamp. This will help to ensure the clamp always sits true on the work piece and prevents unfortunate "ooops I've glued my clamp in place" moments.
Finally check the clamps for square.