To make matching mortises, set limits
I love using my benchtop mortiser to plow lots of slots quickly, but laying out all of those mortises can be a nuisance. This simple trick not only eliminates most of the marking, but also ensures all the mortises match perfectly.
Cut a spacer as long as your desired mortise, minus the mortising chisel’s width. Position and clamp a stopblock to the mortiser’s fence so that the chisel will cut the first end of the mortise. Make the first cut. Then insert the spacer between the workpiece and the stopblock. Make the next cut on the opposite end of the mortise. Clear the space between the two cuts to complete the mortise. Now, you can reuse the spacer for subsequent identical mortises.
—Charles Mak, Calgary, Alta.