Then the top of the chair was the most challenging to model.
Since this is just a prototype, I used 8/4 stock and glued up the blank. I used a cove and bead set (for making canoes) to make the joint between the back and the arm rest portions. This isn't as nice as the joint Wegner uses, but I don't have a 5 axis cnc and I didn't feel like hand cutting these joints.
This gave me a blank about 3.5" thick, which I then cut the underside of the model first. I cut a profile first, using a 1/2" end mill, 2" deep. This just makes it easier for the ballnose bit to carve. I skipped a roughing tool path and just went straight to the finish tool path, which cut 2.5" deep in some spots. I ran this at 400ipm, 18000rpm, with 8% stepover in a raster. I then drilled 4 indexing holes so I could position it with dowels for the second side cut. I held the blank in place with pocket screws in the sides of the waste.
I flipped and cut the second side using the same profile pass (only 1.5" deep this time), and a finish tool path with a 1/2" ballnose. I set up different flat models around the real model so the finish tool path is limited to 2.5" depth of cut. Then I had to glue on another 1.75" piece to carve the top of the back rest. I didn't glue this up in the beginning because my ballnose bit isn't long enough to carve the full depth!
Removed the waste and bandsawed off the tabs, then sanded the completed assembly
I had to make a little jig to cut the mortise holes, because they are at different angles.
Then carefully glued and pressed the top onto the chair. This was difficult and had to be careful because the legs are angled.