Thanks for your purchase! Spindle Boss is a lightweight and accurate way to align round mortises in chair making operations.
Spindle Boss easily slides onto the shank of most standard hex drill bit guides and extensions.
Spindle Boss is primarily used for aligning arm and seat mortises. The arm hole is drilled by sighting toward a mark on the seat (see Chris Schwarz’s methods in his many publications.
The Spindle Boss then nests in the arm mortise and aligns the drill bit in a straight, coplanar angle toward the seat. No matter how accurate your arm mortise angles, your seat angle will always be a perfect match.
Spindle Boss can also be used in the same way to align stretcher mortises. Because those are drilled horizontally, though, the guide has a tendency to spin out of the mortise. To address this, simply take a coarse rasp and rough the tapered surface of the Spindle Boss. This gives enough friction for it to remain in place.