Flat bevel for turning tools
Brad Vietje
>I have been away a few days, and wrote the following response to the concave vs. convex question, then realized very few would see it because it was from about a week ago -- I've re-posted it here. Sorry to chime in so late on this; I've been away due to adeath in the family -- perhaps we can re-open the thread here.
First, I'm very glad we have a more mature group here than at r.c.w., where I have been called all manner of insults for discussing this topic and tool sharpening. Many turners are unable to discuss a topic like this without getting pretty hot under the collar; I just can't see why people get so attached to turning dogma.
Some folks view a convex bevel as a specialty tool for finishing the bottoms of pieces, where it works well. I have long held that a convex bevel was best inside a bowl, and a concave bevel best on the outside of the bowl, for all the reasons Russ stated so well. Therefore, I grind most of my tools with a flat bevel, as a reasonable compromise, and I'm very pleased with the results. I also have one spindle gouge ground with a convex bevel for back-hollowing end grain, where it is much better than a hollow ground tool.
Flat bevels are often frowned upon by people who want to hone their tools a lot, and rightly so -- honing by hand will tend to produce a convex bevel, which many people seem to want to avoid (sometimes for entirely dogmatic reasons, however). The answer, I believe, is to use a sharpening system that produces a flat bevel with a very fine edge, removes very little metal, and is as quick, (or quicker than) honing, thus eliminating the need for most honing. Such a beast can be constructed simply and cheaply by using a 12" disk sander, and a "V" block that can be set to a number of positions for accuracy and repeatability.
Works slick as a trout, really. I built such a system that is cobbled onto the end of an old Shopsmith, sharpening on the "up" side of the disk for most applications, though both sides are used for a flat-bevel approximation of the Ellsworth grind, with the Ellsworth jig anchored in a hole at the correct distance from the spinning disk. I use a 150 grit disk, and I have another 80 grit for any rapid grinding or re-shaping I want to do. I can turn away from the lathe, face the old SS, step on a foot switch, sharpen the tool, and be back at my turning in about 7 seconds.
I hone the inside of the flute for finishing cuts, but not very often do I hone the bevel. This is absolutely the slickest way on earth to sharpen a skew, especially one with a curved bevel -- just set it in the V-block (at the proper location), and rock it from side to side on both sides -- takes about 3 seconds. I hand sharpen a few tools, but use the V-blocks as a jig for most, so a tool can be re-sharpened in 5-7 seconds, removing only the slightest bit of metal, and producing very little heat.
My position is that if you can get a real sharp tool without honing, and without grinding your expensive tools to dust, there would be a lot less honing, and people would be sharpening a lot more often, which is good for the end result.
I find that many people hone a tool 25 times or so to AVOID sharpening, because they either hate sharpening, or have a frustrating experience at it, or have never found a way to get a consistant bevel geometry, so when they finally get the tool to work correctly, they spend the next 3 months trying "not to screw it up", and many end up using dull or mis-shapen tools that hurt their turnings and their enjoyment of the sport. I usually sharpen the tool to maintain a sharp edge, and rarely wait until the tool starts performing poorly; I might re-sharpen 5 or 6 times finish turning a single bowl.
If you've never tried the flat bevel experience, try it -- you may like it.
Safe spinning,
Brad Vietje
Thetford, VT