This section is from the book "The Boy Mechanic Vol. 2 1000 Things for Boys to Do", by Popular Mechanics Co.. Also available from Amazon: The Boy Mechanic, Vol2: 1000 Things for Boys to Do.
Select straight-grained hickory or ash for the springboards. These can be of any width to make up the board to 18 in. wide. The frame part may be of any material of the dimensions given in the sketch. The butt ends of the springboard should be well fastened to the crosspiece with screws, or, better still, small carriage bolts with the nuts on the under side.
The crosspiece at the rear is cut on the angle of the springboard. The front crosspiece is mortised into the frame, and the one near the center is laid on top of the two side rails.
Ill: A Springboard for Use in Connection with a Vaulting Pole or for Turning Acts
The rear crosspiece is either fastened with large dowels or mortised into the sidepieces. This springboard will be of use in connection with a back-yard gymnasium for vaulting and doing turning acts.