Square a Hollow Chisel by Eye
The hollow chisels used on mortisers are difficult to square to the fence, even when using an engineer’s square. Here’s an easier way to get the job done.
First, use a spring clamp to secure a straightedge to the chisel. Second, rotate the hollow chisel until your eyes tell you the straightedge is parallel with the fence. If you don’t trust your eyes, measure the distance from each end of the straightedge to the fence; when the two measurements are equal, the chisel is parallel.