To make a 6mm Schlumpf cone washer:
Start by slicing off some 2" 6061 Aluminum barstock using a special non-ferrous metal cutting blade on a 12" chop saw:
Chuck it in the lathe, turn the OD, face it, cut the 45 chamfer, then remove material from the ID, starting by drilling, then follow by boring out the extra material:
Keep boring until the desired ID is reached:
Part it off, cut the reverse inside taper (not shown) and clean it up, (note the real Schlumpf part is on the right):
Stock 4mm spacer on the right, homemade 6mm spacer on the left:
Slide it on the Schlumpf drive (4mm aluminum Schlumpf on the left, 0mm steel Schlumpf on the right):
Hopefully this will work where the 0mm and 4mm washers failed.
I had a long day today, getting this made feels good. Hopefully it will do the trick!
Note that they recommend aluminum spacers with steel frame bikes and steel spacers with aluminum frame bikes.