William Duffield
What was I thinking when I put this together?

Yes, of course, drilling it on the lathe just about insures concentric mortises. I have a scroll chuck, a steady rest, and a keyless chuck to hold the bit in the tail stock. I have a very limited selection of end mills, but I think my brad point bits would work better than the Forstners in end grain. The limitation is the length of my lathe bed. It's sufficient for most chair parts, but I have an additional 8" under the DP chuck.