
I  made this chopping block a little while ago.  This is a good way to get  a stable chopping block if you don't have any large rounds of wood.   This block is something like a block I once saw, but in reverse.  In the  version that I saw, the fork was a large tree crotch, and there was a  single smaller limb used to complete the tripod.
In this version, I used a Maple log about 6-8" diameter, as well as a  forked limb about 1" diameter, all longer than I wanted them to finish.   I bored a 1" hole in the larger log at an eye-balled angle, chopped  down the forked limb to fit the mortise, and stuck it together.  Using a  tape measure (any old stick with some notches in it would work), I  measured a good height for a chopping block, then transferred it to the  block and sawed off the excess.  I stood it up, sawed the top off  approximately level, and it was done. 
Because it's a tripod, it will be stable on almost any surface.  It's  also small and light enough (and can be taken apart) to travel in a  car.  It is very stable and stiff, though, if you orient your heavy  blows so that the force will travel down the large leg.
I'm not sure, but I think I probably found the original inspiration over on the bodger's forum.
 

