Steel rod run through the hickory board which is bolted to bench top.
Sits in another piece on floor with an hole to accept steel bar,(aka.bearing)
The rotational resistance is achieved by the cross bolt in the board holding the bar vertical.
The large board with the steel on the bottom,is an fixture i made for working on national guitars.
The shaft fits the sleeve of the vertical shaft.
I also have a shaft with a plate,on which any bench vise can be mounted.
McKenzie said he used one while working on Purdy's in England.