Mark Koenig presented a descriptive lecture on initial shaping and sharpening of woodturning tools, particularly the bowl gouge, at the April 4th meeting. He began by describing the three basic flute designs utilized in bowl gouges; the “U” flute: straight sided with a “U” shaped bottom, the parabolic, or “Superflute” :which has a continuous curve and the “V” shape: straight sided with a sharp curve at the bottom. Mark feels the “U” shape is best only for “bottom feeder” gouges while the parabolic flute presents the least sharpening challenges and allows good chip ejection. He is not a fan of the “V” shaped flute.
The next consideration he illuminated was the choice of nose angle. Some professionals, such as Stuart Batty, are proponents of the “40-40” grind, where the nose angle and wing sweep angle are 40°. David Ellsworth is at the other end of the spectrum with a nose angle nearer to 65° and long wings. Mark prefers a 55° nose angle and, as Glenn Lucas recommends, wing length equal to tool diameter; a 5/8” diameter gouge’s wings would be 5/8” long.
Mark strongly advocates the use of a sharpening jig; A Tormak slow speed system, a Oneway Vari-Grind or Woodcut Tru-Grind jig or a Robert Sorby Pro-Edge belt grinder. Of these systems, the Oneway Vari-Grind or Woodcut Tru-Grind jigs are the least expensive and most widely used.
Mark demonstrated use of the Oneway jig and spent time explaining the relationship between the pivot bar set back, the tool projection and the leg angle. By following recommended dimensions and angle settings these jigs allow consistent reproduction of the tool grind, which, in turn, reinforces muscle memory as the tool will cut predictably.
He showed how he establishes the nose angle first on a new tool by setting the grinder platform at the required angle on the coarse wheel and grinding the tip of the tool to define the nose. He then marks the desired wing length and turns the tool flute side down and slides the tool up and down the face of the wheel to define the wings.
The tool is shaped on the coarse wheel and sharpened on the finer wheel. By using a jig very little metal is removed each time the tool is sharpened as only the fine edge is being re-established. Mark made a point of mentioning a couple of videos from our library and YouTube that he highly recommends: Glenn Lucas Sharpening Video (Library) and Thomson Tools ; http://thompsonlathetools.com/sharpening.He strongly believes that anyone having difficulties with their sharpening should watch and follow one of these videos and establish a grinding/sharpening routine.
Spindle gouges are sharpened on the same jigs as bowl gouges.
Mark also covered sharpening the Spindle Roughing Gouge and negative rake scrapers (sometimes referred to as “skews”). Neither of these tools requires a jig to sharpen.