Oscillating multi-tool stationary mortiser

[threesixesinarow]

I use this machine for cutting rectangular mortises. I had bad results with hollow chisels I made the size I needed, and bought a Harbor Freight multi-tool just to rule out before building something less crude. It worked well enough that I haven’t started that - still, I don’t know how durable this one will be.

It replaces the regular head on my radial drill, and I use table clamps to keep work from moving with the blade. I plan to add a kind of presser foot, too, which will help positioning.

I tried a few different blade designs and for this size three teeth about 1/8” apart seemed to work better than just two teeth, or else more. There are slots both sides of the blade so chips can push out.