you can see in the drawing at the right, the guide starts off as a pair of wedge-shaped
support blocks that hold the top at a 25° angle. To square up the chisel (and
keep it from shifting), it sits against a wood cleat that's glued into a dado
cut in the top.
To set up the guide,
place the chisel against the cleat and slide it down until the bevel is resting
on a flat surface (not on the sandpaper). Then clamp the chisel in place and "scrub"
it back and forth across the sandpaper. Note: I start with 180-grit sandpaper
and work up through 400 grit.
Have a nice weekend,
Online Editor, ShopNotes