As with most project I make, I started by googling it up to see what is out there. Then I look around the shop and use whatever I can scrounge. In other words, I rarely, if ever build, something as per published dimensions. I simply make it fit whatever stock I have. Make it fit is my motto in the shop :-)
In this case, I had some leftover pieces of maple from the days I was building shadow boxes to present to retiring service members. Incidentally, I made my own shadow box to be presented to me when I retired :-)
There are 4 pieces to them; the 2 jaws (one fixed and one sliding up and down the post), the post flat bar (you can use metal for a stronger clamp if you like, I just used maple) and finally the pivoting cam. I also added cork faces to the jaw parts, it gives some cushioning and help grip better.
You can make them to whatever size you need/want, I simply sized mine to reach inside the sound hole to be able to glue the broken ribs and glue the bridge. These were my only dimensions criteria's for this job.
So mine ended up with a flat beam length of 15-1/4 in long X 7/8 wide X 1/4 thick the jaws are 7-1/2 in long X 1-3/4 wide X 3/4 thick
Yes, I used Sketch-it-Up for my plans :-)
I used a 1in Forstner bit for the cam's finger clearance hole in the movable jaw. I tried using other sizes Forstner bits to make a clean round cut out for the jaws but in the end it was easier & faster to just mark my circle using the protective plastic cover of the 3/4 in Forstner bit and eyeball the cut with the bandsaw followed by a quick clean up with the Oscillating Drum Sander
Similarly the slot for the cam action to work, is cut with a bandsaw using a fence. I then added a hole to prevent the piece to break off under pressure (a stop hole)
The through mortises are 7/8 X 1/4. The one for the fixed jaws are a tight fit, the one for the movable jaws are a looser fit, it must be able to cock under pressure to securely grip the works (similar action of a holdfast on the bench). If you use a metal bar, you should add 2 metal pin for the bar to bear against.
I used a dado blade in the tablesaw to cut the slot for the cam lever. On this clamp, I'm a bit off center, corrected on the others.
I epoxied glued the flat bar to the bottom jaw and reinforce the connections later by drilling and
epoxying 2 nails which I cut to make steel pins.
The cam action piece is 1/4 plywood, the only tricky part is the offset hole on it. It depends on this offset to push the bottom lip of the movable jaw. It is also secured using a steel pin carefully epoxied in place (try not to glue the cam in place. Don't even ask) :-) If you want fix ability, uses a steel roll pin instead.
I looked at the dollar store to find some cork pieces, and came up with drinks coasters. The cork with its back up is 1/4 thick. It make a big difference on the clamps operation, Being faced with a solid base, it was too easy to glue the cork pieces using regular yellow glue and using the clamp pressure to do it. And that is about it. Sorry I do not have any pics in progress, it was a quick project of necessity. If anyone needs more info, just let me know.
Bob, who played a bit with SketchUp, but find it a lot faster to just sketch it up on paper :-)