Oscillating multi-tool stationary mortiser

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.

Attachment 26239 Attachment 26241

Attachment 26240 Attachment 26242