As a violin maker I am always beset with the problem of sharpening a wide variety of in-cannel and out-cannel gouges. I stumbled across the solution this evening!
Starting with a length of 6-inch plastic drainpipe I cut out a section about 8 inches long and then split it longitudinally so as to retain about one third of the circumference. On both surfaces of this I attached a graded series of pieces of 3M micromesh self-adherent abrasive approx. 2" by 2". By varying the strength of the grip across this device the radius can be altered at will to suit the form of any of the larger gouges.
The tube can be squeezed in a vice to get the correct radius. The outer surface is used in the same way for the in-cannel gouges and for honing the flat side of the others. A little water and you are in business! For the smaller gauges a similar device can be made from plastic- or rubber tubing of smaller caliber.