Is there an advantage having a flat grind versus a concave grind on a bowl gouge.Sorby pro edge vs grinding wheel.Need to make a decision to buy a sharpening system
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Is there an advantage having a flat grind versus a concave grind on a bowl gouge.Sorby pro edge vs grinding wheel.Need to make a decision to buy a sharpening system
For years I used a 9" disc sanding disc with a homemade jig to flat sand several sizes of gouges to a consistent angle. Gave it up when I discovered that a radius ground(like a CBN or stone) seemed to be more willing to pick up a curl on a piece. Just my 2 cents here.
Could ask same question in flat work. Chisel off a grinder or a flat water stone. I think it is just a personal feel or philosophy. Most experienceed turners only use a small area just behind the cutting edge. Float the bevel, don’t rub it.
When I do a regular resharpen, I do it on the radius of a grinding wheel, using a sharpening jig so the end is concave. But if I am just retouching it, I'll typically take a small hand diamond card or file. Because of the concavity (real word?) the card only removes material on the outer edges. As a result, it doesn't take very long and sharpens nicely. Eventually when I see that move of the concavity is gone, then I'll take it back to the grinder.
Many sharpening jigs for gouges seem to assume that you are using a wheel. Such as Wolverine, One-way variground, Ellsworth, Captain Eddie's, etc. I built the $2 Capt'n Eddie version.
I have a Tormek 7 unit, had it for around 10-12 years. It is a good system, I understand it and I think it is really great. My turning tools are razor sharp and as consistent as I believe it is possible to be.
At my Men’s Shed, we have the Sorby Pro-Edge system, all of the turning chisels there are obviously flat. I pondered this exact same question myself and decided to test it. I happen to have two identical bowl gouges, so I sharpened one on the Sorby and one on the Tormek.
After one sweep of either pristine gouge, where they were like a hot knife through butter, I was away and wondering if I was still able to notice the differences. A canny friend who was holding the chisels, handed back the same chisel on one swap over; I didn’t notice. I don’t believe there is a real noticeable difference or if there is, it really is minor.
The real advantage of the Sorby system is in shaping. Shaping on the Sorby literally takes a few minutes and a some belt changes . With the Tormek I know from experience, that shaping takes time, real time. Maybe 15 minutes to re-shape a wide (big) skew chisel, then you sharpen it, which takes maybe another minute or two.
I think if I was purchasing a sharpening system today, the Sorby would be pretty much on the top of my list. For absolute razor sharpness, both pretty much do the same thing. As for flat and convex shape, it didn’t matter to me.
Mick.
I have a Tormek, a grinder with 2 stone wheels, a grinder with 2 1" wide CBN wheels and a grinder with 2 1 1/2" wide CBN wheels. I have the Wolverine system (several), the Sharpfast system, Nova Sharpening system, Tru-Grind system and the Vector Grind system. My grinder that only I use is the one with the 1 1/2 CBN wheels and it is setup with the Vector Grind system. The Vector Grind system is made by JoHannes Michelsen and it replicates the by hand grind that he and Chris Ramsey use which is virtually uncatchable. A repeatable grind and CBN wheels insure me that the tools will last probably 10 times longer than stone wheels. Couple that with my Thompson Lathe tools and one swift pass on the CBNs gives me a long lasting edge with little grinding wear. For new woodturning students I have them use the Sharpfast system as that system keeps the tool in the center of the wheel so no accidents by falling off the edge of the wheel. Every one of the systems work and I found no major differences with sharpness achieved with any of them, the main difference being that the Vector Grind gives a lot less chance of a catch.
I don't think there are any mechanical differences as in how the tools perform. Other than that, with your bowl gouges, you want to grind off half or more of the bevel heel for use when turning the inside of a bowl, or any concave surface. This keeps the bevel contact spot where you 'rub' the bevel closer to the cutting point and you don't leave heal bruises in the wood. Not necessary on a convex surface, but all of mine have the heels ground back.
robo hippy
I think what you are thinking about here is called hollow grinding. With things like chisels and plane irons, hollow grinding has a specific purpose, that being to make it easier and faster to hone the edge. Outside of that there is no reason that a hollow ground edge would perform better than a "flat ground" edge. But with turning tools, the rules are somewhat different. Most turners have a preferred method of sharpening that works best for their particular application. Grinding away the "lower" portion of the bevel to create clearance for cutting down the inside of a bowl as Reed mentioned is a good example.
This is the tool Chris Ramsey ground freehand during a cowboy hat demo. I've tried grinding one like this and it works well - a convex bevel, not flat or concave/hollow. It illustrates how little bevel is actually needed and used.Quote:
Originally Posted by Bill Blasic
He added the very short cutting bevel with a single pass after shaping the tool. I highlighted it in red to make it easier to see.
Attachment 401848
(sorry, poor cell phone photo)
I'm sure a jig would be a useful substitute for experience for many of us.
JKJ
Attachment 401888
A quick photo showing the reference tool Chris Ramsey gave me a couple months ago (bottom) and a gouge sharpened with the Vector Grind (Top tool).
The Tormek gouge jig can give this type of grind as well. There is a sliding collar that can create either steps or a smooth convex curve. I use it a lot to round the bevel to minimize burnishing from accidental contact with the heel when turning coves. I think that and the clearance on tight inside curves is the big advantage with the grind Ramsey uses.Quote:
Originally Posted by Bill Blasic
If used properly, only a very tiny portion of the bevel is ever in contact with the wood.
Attachment 401891
The rest of the bevel doesn't matter except when it gets in the way, or as mentioned earlier, when honing by hand.
JKJ