After watching this video, you can download the free PDF document and make it easily. There are many 90 degree corner clamp videos on youtube. But this is a little different from what I did, let's see, do you like it?
Making Video :
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PDF Download : Right Angle Corner Clamp Making
I make long C clamps using some hard plywood. You can do a lot of compression with these extra powerful clamps. It is very useful thanks to its long arms.