Can crusher design, Mark II.
I have inspected the wood I already had stored in my garage and come up with the much simpler 5 piece design at left using only two pre-existing sizes of wood.
It features a 50x80x80 mm top jaw with 200mm travel mounted on two vertically sliding 50x50 mm uprights on either side of a 50x80 mm central post/lower jaw.
The 50x50mm lengths are leftovers from my deck railing. (See the "Contact" page illustration, link at top.)
I have just installed a new USB enabled, .mp3 playing stereo in my recently acquired car, plus new speakers as the existing ones sounded atrocious and turned out to have no, repeat, no diaphragms (cones). I have just experimented with extracting the large magnets from the old speakers, and now find the two disc-like pole pieces are exactly the right size and shape for jaw plates, complete with locating projections.
The top jaw and foot bar are made from the same stock as the centre post/lower jaw. The foot bar is shown edge-on, and will project 80 mm out from the uprights
Undiagrammed are a big coach bolt through the top jaw and outside uprights, and some big screws to take the foot force from the foot bar to the outside uprights.
There will also need to be a wall protector back plate made of aluminium sheet I have, about four retaining tabs to keep the outside uprights against the back plate and parallel with the centre post/lower jaw, and a return spring of some sort for the outside uprights. A big used bicycle-tyre rubber band might do.
Pictured at left are the pole pieces, together with the extracted magnets.
The magnets are stacked and repelling each other, the top one is hovering and will spin in that position if given a light push.
I don't know what real use the magnets are, but I will be sure to blog it if I find one!