Roughing Out the Handle and Forming the Razee
Using a handle off of the other of my great-great grandfathers planes (a jointer) as a pattern, I traced out a new handle for this plane - the only changes to the original were so it could be fit into the mortise of plane, and I lengthened the horn a bit because the one on the old handle was a bit too short to be comfortable, at least to me. After roughing out the outside of the handle on the bandsaw, I use a couple of forstner bits to rough out the interior of the handle.
After cleaning up the shape of the inside of the handle with a couple rasps, I use it to determine the shape of the "razee" part of the back of the plane, then cut the body to the same shape on the band saw. The razee should be the same shape as the front of the handle, so it fits all together in one piece. The bottom of the handle should be about 1/2" above the bottom of the plane, and the mortise for the handle about a1/2" deep or so - don't worry, that confusing mess of sentences will become clear as the pictures progress... Here, you can see what I mean, I'm holding the handle up to the body of the plane after I've cut the body of the plane to match the curve of the handle.
Now that the razee is cut, I use a 3/4" forstner bit (the handle is about 13/16" thick) to rough out the mortise for the handle. It's best to use a fence on the drill press to keep the holed drilled at the same distance from the edge, straight down, and to an even depth:
After all of the holes are drilled, I use a marking gauge to scribe the outer lines for for the handle and finish the holes up with a good, sharp paring chisel.
Can't forget to smooth out the bottom and corners of the mortise as well. I spent quite a bit of time, working from the heel of the plane and working forward, test-fitting the handle frequently. I squared up the mortise at the farthest forward portion to match the squared cut of the handle, rather than try to round the front of the handle to fit a round mortise, which I think would be much more difficult.