Curiously, how a bowl gouge’s cutting edge is ground can affect how well it performs as a turner attempts to make deep, closed forms. To improve the cut, I grind my gouges in a specific way that includes a second bevel. To fully understand the benefit of secondary bevels, we need to first look at how a bowl gouge works and how its grind has changed over time.
We see a traditional bowl gouge of about 1970 vintage. The flute is U-shaped, the edge is square to the axis of the tool, and the bevel is ground to a uniform 45°. It cuts shallow bowls of an open form very well. However, it does not do as well on deep, closed forms. That’s because the geometry of the grind actually gets in the way of the cut.
In the 1980s, Irish turners found that by sweeping the face of the tool back at an angle and grinding the bevel asymmetrically, the gouge cut much better in deep, closed forms. Typically an Irish grind has the nose bevel ground to about 70° with the sides at 30° to 40°. The grind can be adjusted for even deeper cutting.
As a bowl gets deeper, the height of the sidewalls increase and the curved transition between the walls and the bottom becomes a much tighter radius. Since the tool must be presented very near the axis of the centers, it is like working in the bottom of a mineshaft. Our traditional gouge would need to be about 70° from the centerline to cut effectively. Even the Irish grind suffers here because the heel of the nose bevel forces the cutting edge up and away.
The solution to the problem is to grind a secondary bevel, thereby shortening the rubbing bevel and allowing much tighter radiuses to be cut. I grind the secondary grind without the aid of an additional specialty jig by simply setting the pocket of my Wolverine Jig closer to the grinder.
How wide to make the secondary bevel depends on how narrow you want the rubbing, or primary, bevel to be, and this will be dictated entirely by your work. Even for shallow bowls, a secondary grind is helpful. All of my photos in this article illustrate bevel sizes I think are appropriate for average faceplate work. As your skill increases and you tackle deeper vessels, you will benefit from grinding the secondary bevel bigger and the rubbing bevel smaller.
In the past, I have resisted teaching secondary grinds in my basic turning classes for logical reasons. My feeling was that the biggest struggle for a neophyte is to learn to “ride the bevel,” which is a sense of feel much like riding a bike or snow skiing. My logic was that the bigger the bevel, the easier it is to sense being on it. Now, after introducing the secondary grind idea on the first day of the faceplate section of some of my basic turning classes, I can say that I was wrong! If anything, the neophyte has an easier time with a secondary bevel than without it.
One, Two … Three!
Recently my friend Johannes Michelsen, who turns elegant wood hats, has come up with a tool which he calls the Vector Grind Fixture. It produces a secondary bevel plus yet a third bevel he aptly calls the tertiary. Happily, Johannes’ jig marries into the Wolverine System and represents an improvement over their Veri-Grind Jig. The tertiary grind effectively radiuses the primary bevel’s heel, allowing the gouge to turn tight radiuses with aplomb. There are some other plums in the Vector pie, too. Firstly, you can create a true 45° rubbing bevel with a curved cutting edge on each side a bevel is created. This means that no catching corner where the bevel meets the flute is possible. The curved edge also has less chance of the turner being overwhelmed by getting the entire side bevel cutting suddenly. While the 30° side bevel that is typically achieved on the Irish grind is OK for green/wet wood, in practice you’ll find that it does not do well when cutting dry wood. The 45° attack angle gives the least tearout, wet or dry, against the end grain — which happens twice a revolution in faceplate work. The Vector Fixture is very well-made and costs about $150.
The Vector Grind Fixture
While the angle of the nose grind with a Veri-Grind Jig is controlled by articulating the strut that fits into the Wolverine Pocket Jig, the Vector Fixture accomplishes the same thing by how far the tool protrudes from the face of the fixture.
The Vector Fixture comes with a nifty device that mounts on your grinding table for correctly locating the gouges. The gouge is inserted flute down, and the thumbscrew locks against the round bottom section of the gouge. This allows the tool to be ground until there is no flute left.
The primary grind is done in halves, with the strut of the Vector Fixture in the holes that are left and right of center. In the photo, I am grinding the nose and right half of the gouge so the strut is in the hole to the right of center. For the left half of the tool, the strut goes in the left hole. Grind from the far side of the nose to the end of the bevel in a slow, continuous sweep.
For the secondary grind, the strut is placed in the center hole the farthest from the grinder. Grind until the rubbing bevel (the cutting bevel) is between 1/16” and 1/8 ” wide. Adjust for smaller and larger gouges proportionally.
For the tertiary grind, the strut is placed in the center hole closest to the wheel. This turns the heel of the bevels into a radius, making for a gouge that can turn the tightest of corners.
Cut the Chatter
One final benefit to secondary bevels in general: When cutting on the outside of a bowl with a standard Irish grind, it is common to set up an unwanted chatter pattern caused by the interplay between the cutting edge and the heel of the bevel on the half-spherical surface you are creating. Like a corduroy road, it gets worse as the cuts progress. Lifting the handle slightly to make the tool level on the rest often corrects this problem. A secondary grind, no matter how it is achieved, is practically immune from this chatter problem.