At home during a holiday, I found myself in need of a clamp larger than what I already had. With most stores closed I decided to make my own based of the Bessey clamp design. Total cost was $0 using scraps of metal I had laying around. compared to store bought ones which easily run for $50.

Parts list:
1x nut (mine is 2" long)
1x bolt that fits the nut
2x washers
1x 20" of 1/4" thick x 1" flat bar
1x 5" of 1/4" thick x 1.5" flat bar
1x 6" of 1/4" thick x 1.5" flat bar
1x 2" round bar

Step 1:

first step is to weld the end of the 20" long 1" flat bar onto the center line of the 1.5", 5" long flat bar.
Obviously your going to want everything as close to 90 degrees and parallel as possible so everything lines up nicely when complete.

On the end of the 1.5" bar I welded a washer for a nice clamping surface.

Step 2:

Next is the sliding arm.
Draw a center line down the middle of the 1.5, 6" long bar and make a mark about 1/2" from the bottom and another 1/4" about that mark.
Sorry no picture of this step so i drew one :)
I used a drill slightly larger than the bolt and made a hole 1/4" from the top for the tightening bolt
I used a plasma cutter to make the slot for the long flat bar. Make the opening slightly to small to fit the flat bar and use a file to take it down by hand so the bar just fits in but also slides smoothly.
You don't want it to be tight but if its too loose then there will be too much play and it will operate sloppy.
This is the probably the most important part of the whole build, explained why on the last step

Step 3:

Take the bolt and weld the 2" long round bar on the end. this will be used to tighten/loosen the clamp.
Protect the treads from damage of weld spatter

Position the nut on the sliding arm over the hole you drilled and weld in place.
Thread the bolt through and weld a washer onto the end. This will be he other clamping surface. Be sure to grind down the welds to a smooth finish so it damage the work piece.

Step 4:

home stretch ...
Slide the sliding arm onto the main shaft and double check that everything moves smoothly, then place a tack weld at the end of the main bar to prevent the sliding arm from coming off.

Viola! finished. Grab some things to clamp together and test it out.

Step 5:

How to make it work..
grab 2 pieces of wood
put them together
move the sliding arm up against the piece being clamped
tighten down on the tightening bolt and your set

notice as you tighten, the sliding bar will angle back a bit causing the two bars to "lock" together, keeping everything tight and preventing the sliding bar from moving.
If you make the opening for the main shaft too big the angle it tilts will be greater which is why you want it as tight as possible while still being able move freely

I mainly use this for clamping metal items for welding, for clamping to oft materials (ie wood) I put felt pas on the contact points.