I've been wanting to make some of these for some time, after reading an article in Fine Woodworking about it. I got a screwbox and tap set here for a reasonable price, it is not the best set up, but I got it to work fairly well.
Attachment 40634 Attachment 40633
They are made from Hard Maple and time will tell how long they last, but it is amazing the clamping power you can generate
These two took me most of the day, but as they are prototypes, that can be expected, I had to figure out how to make them and how to get the screwbox to work well, out of the box it did not work well at all, but I did get it working nicely by the time I was done.
I'll certainly be hanging onto more scraps and setting them aside for clamps