40/40 Grind

The “40/40” grind is advocated by Stuart Batty (Allan's son), and is used by his protégé Ashley Harwood. They both advocate hand grinding on a platform set for 40° (a number of companies make such platforms).

My experience is that this shape is very useful for the really hard woods used in ornamental turning. Examples include African Blackwood and Desert Ironwood (both with Janka hardness measures > 13,000 N).

As shown in the diagram to the right, the wings are not swept back as far as the diagrams below, but the α remains the same. Also, the wings (on the rake) are recommended to be flat, not convex. This is because the wings are not a key element of the style Stuart uses for his work (unlike that advocated by David Ellsworth). I have found it difficult to produce truly flat wings; mine are more convex. This has not decreased the usage of the tool's grind shape for me.

Stuart Batty has a number of great videos on Vimeo showing his SB Tools, including some on sharpening.

Flute Note: The bowl gouge sold by Ashley Harwood has a parabolic flute. Feedback I've seen regarding this grind shape has noted that the parabolic flute seems to work best for this grind.

The profile shown to the right with long swept back wings can be achieved by adding more side-to-side swing of the tool when sharpening it (i.e., grinding the wings further back for a higher rake angle -- more information about this is in the comments below).

The Tormek handbook, Water Cooled Sharpening of Edge Tools, advises that this grind shape is not recommended for starter-level turners as it can be somewhat aggressive, but many others feel that 40° is the optimal grind angle (except for bowl bottom gouges, where 60° is recommended).

Note: I do not see this grind discussed often in woodturning fora or at woodturning tool sharpening events.

The Tormek handbook, Water Cooled Sharpening of Edge Tools, recommends that this grind shape is for turners of all skill levels.

Others feel that 40° is a far better grind angle (except for bowl bottom gouges), especially if pursuing a multiple bowl gouge workflow.

Note: I do not see this grind discussed often in woodturning fora or at woodturning tool sharpening events.

The "Irish" profile with swept back wings was pioneered by Liam O’Neil, and can be achieved by adding more side-to-side swing of the tool when sharpening it (i.e., grinding the wings back further).

Allan Batty recommended this angle, though Stuart Batty noted that his father's recommendation for this angle was based on his production work being made easier (vs. using a second bowl gouge for bowl bottom work).

Stuart's stories of working for his father are worth the price of admission to his classes (oh, and the instruction is good too).

This is a good grind for bottoms of shallow bowls.

The wings do not need to be swept back, and indeed the rake angle may tend towards 80°.

The larger edge angle is beneficial when turning deeper within bowls.

Tom Wirsig noted that this angle, coupled with a U-shaped flute, is best for figured woods, also noting that it must be very sharp (see also, "Tips for Turning Figured Woods", in the October 2022 edition of "American Woodturner"). Tom also recommends a shape where the wings are not swept back, with the rake angle tending towards 80°.

This is a good cutting angle for bottoms of the bowl, especially a deep bowl.

The rake angle (wing sweep) will look like the one shown above for 55°.

The “Ellsworth” shape, made famous by David Ellsworth (one of the founders of the American Association of Woodturners - Member #1) has wings which have a very pronounced convex shape.

David turns a lot of wet wood for the objects he makes, and I have found that this shape works well for such turning. I have also found that this shape is not as usable for really hard woods (i.e., Desert Ironwood or African Blackwood).

These wings are a key element of the style David uses for his work (unlike that advocated by Stuart Batty).

Flute Note: The bowl gouge developed by David Ellsworth has a parabolic flute. Feedback I've seen regarding this grind shape has noted that the parabolic flute seems to work best.

Notes & Comments

Information regarding Grindstones

Marty Kiminsky noted that 40-65° is generally recommended for this tool. He further noted a personal preference for 40° and 60°. See also, "Woodturning" magazine, issue # 352.

Rake Angle Grinding Notes:. The best shape for the edge is slightly convex or flat.

Good	Slightly Convex - best shape	Flat - acceptable shape
Bad	Overly Convex	Concave
	Cause: excessive grinding on the front edge.	Cause: excessive grinding on the wings/sides.

Image courtesy Tormek

The wings can be extended for a greater rake angle by the way you grind. The rake angle is increased when you spend more time grinding on the wings, and when you increase the amount of swing you use when grinding.

The diagram to the right shows this movement.

When the tool gets too short to be held by the jig, you can grind off the top as shown in the upper tool below. This flat area allows for the jig to hold the tool without the tool slipping or rotating.

And when it gets even too short for that, consider making it into a round negative rake scraper (great for bottom corners of boxes), a beading tool, or a point tool.