Not often, but most commonly with green sapwood, if the flute is presented in line with the approaching wood’s velocity, tear-out of parallel grain may be very difficult to avoid. A more horizontal flute presentation probably allows the lower, upward-facing flute surface to act like a hand plane’s chip breaker.
If you want to turn the truest possible cylindrical spindle, and avoiding tear-out was of no importance, you should use a wide skew presented at zero side rake (Photo. 11). Similarly, to minimise rippling, the component of the shaving width parallel to the direction of tool traverse should be as long as possible.(Photo. 12) This of course conflicts with the desirability of at least a 70° side rake for the active edge for finishing cuts which greatly shortens the horizontal component. How to achieve an optimum compromise? Increase the flute radius of the active edge. I therefore use big gouges.
If you use a hollow ground or effectively straight in longitudinal section bevel, when traversing along a concave path, to achieve a desirable near-zero clearance angle, the bevel heel must act like a fulcrum (Fig. 4). The likely result is a ring of paler crushed cells. In some woods this damage can descend to a considerable depth. By using a convex bevel whose convexity is tighter than that of the concave path, crushing is avoided. Also when hollowing in layers where the traverses of finishing cuts are short and overlap, it is easier to feather the start of a cut.
I first showed how to grind convex bevels on page 293 of the 1995 edition of The Practice of Woodturning, and later on page 50 of The Fundamentals of Woodturning. To date I am not aware that anyone else has adopted convex bevels despite their simple and obvious logic, although I note the increasing promotion of compromise two- and three-facetted bevels.
Grinding convex bevels is easy. Dress the periphery of a grinding wheel concave with a dressing stick (Photo. 13). I adopt a 35-mm-diameter recess because it is the tightest concave curvature I turn in bowl surfaces. You can vary the convexity of a bevel by the tilt of the gouge blade which has to be manipulated by hand (Photos. 14 and 15). I invariably hone all the tools I use for spindle turning, but because in bowl turning I present active edges with high side rake and the edges are therefore cutting largely by sawing, I don’t bother to hone.
A concave grinding wheel periphery can also be used to grind hollow-ground bevels on gouges (Photo. 16).