The fixture is very simple – A lever arm rides up a form as the blade begins to cut the block. The form shape determines pitch distribution – A straight line produces a helical pitch distribution.
Once cut, the surface is lightly sanded and any imperfections filled with wood filler. With Poplar blocks, the surface is also filled with a thinned wood filler, then lightly sanded for a nice smooth finish. Balsa blocks are not filled in this manner and the surface will be rougher than Poplar. I leave it to the purchaser to finish-sand the block to their desired smoothness.
You may find markings on the bottom of the block at 1″ intervals. This is for checking the accuracy of the blocks making sure that the pitch angles at the stations are what are expected.
I can easily cut Poplar to around 22″P. Anything lower than this will need to be in Balsa. I have successfully cut short blocks in pitches as low as 12″, but 14″ is the limit to what I will cut in the future. 12″P twists the blade too much.