What is your preferred grind on Bench Chisels? Flat or Hollow grind? I have the backs honed flat down to 1200(paper on glass). Have access to the New Jet “tormek” clone and am debating wether to go that route or my old way of doing them flat the Scary sharp way.
Work Safe, Count to 10 when your done for the day !!
Bruce S.
Replies
Hollow grind with a hand-operated grinder. Absolutely amazed at how fast it is. The hand-operated grinder is the best sharpening tool I've ever bought, out of a candidate pool of many.
I still use a small hand grinder, like yours, for my ordinary chisel and plane blade sharpening, and I can't think of a simpler, less expensive, way to get the basic grinding done.
John White, Shop Manager, Fine Woodworking Magazine
Just curious where to look for a grinder like yours--that looks like a good solid tool.
Max
Max,
Look at flea markets, particularly in small towns, or estate sales where there's a barn or old workshop and a bunch of old tools involved. Good luck, Ed
Sorry to jump in late on this post, but I had a related question regarding hand grinders. I've had great luck with a Praire brand hand grinder with a 6 inch white wheel.
Question: The wheel has some 'wobble' as it spins round. Is this normal/acceptable? I've never used a different grinder, so I don't know. It seems to get the job done - I follow up with free-hand honing on waterstones. Can such wobbles be fixed if necessary?
After dressing the stone, if you still have wobble, that doesn't sound right to me. Might be worth it to take everything apart and make sure that the axial load-bearing shaft (that the stone rides on) isn't bent. If it continues to be a problem, probably smarter shop-skilled guys than me can help answer your questions.
Forgive me for butting in, but FWIW, while I don't have a hand grinder, I do use 6" white wheels on my slow speed electric. I've found the norton wheels I get are almost invariably slightly out of perfect round when I receive them and need some truing with a diamond point. If I don't true them, the result is a wobble of sorts.
Thanks, Samson, good point that I forgot to mention. The white (well, it's kinda blue, actually) aluminum oxide wheel was wobbly from day one when I bought it for the hand grinder. I'll try re-attaching the nasty gray wheel that came with it. If that wobbles I'll know my problems in within the grinder itself, yes?
It depends upon whether the gray wheel is true, I'd guess. If you haven't already at some point, I'd just try truing the white wheel (with a diamond point or diamond bar wheel dresser) and see if it takes care of the wobble.
Eskimo,
The othe rreason for having a wheel dresser is that the wheels get clogged with debris from sharpening, so its worth putting one over the wheel pretty frequently (like every week or so) to keep a fresh surface on the wheel. Sharp grit onnt eh wheel means less time and less heat build up.
dave
Thanks, everyone. I'll give it a crack with a diamond wheel dresser. Thanks!
The Eskimo...
On high speed grinders, a wobble creates vibration that affects the grinding, the bearings, and even risks cracking the wheel, but on a small hand cranked grinder the wobble is common and harmless, the chisel just moves up and down with the stone.
If you are going to true up the wheel with a diamond dresser, the dresser will have to be rigidly mounted on a support so that the diamond only strikes the high spots on the wheel. I use a star wheel dressing tool to renew the face of the wheel when it is glazed but a star wheel won't true up an out of round wheel.
John White, Shop Manager, Fine Woodworking Magazine
Bruce
I hollow grind all my chisels (choice of high speed grinder or hand cranked wheel), then freehand them on waterstones. The two-point registration is much more stable than a single (flat) area. The latter will rock and you end up honing a rounded bevel.
The alternate to the above is a microbevel via a honing guide (LV Honing Guide)on a flat bevel, which is my preferred method for BU planes. BD planes also get a hollow grind.
Regards from Perth
Derek
Bruce,
Flat grind, free-hand on water stones.
Beste Wünschen auf eine Fröhlichen Weihnachten und ein glückliches Neues Jahr!
Tschüß!
Mit freundlichen holzbearbeitungischen Grüßen aus dem Land der Rio Grande!!
James
What is your preferred grind on Bench Chisels? Flat or Hollow grind?
Are you suggesting that some contend flat vs. hollow makes some difference in performance of the chisel? If there are camps of flat grind versus hollow, I'd love to know their theses.
For me, my preferred sharpening method, come to after trying many, drives the bevel architecture, and not vice versa. I like using honing guides on water stones (some times I start with a diamond plate to bring a neglected chisel up to readiness for the stones - back flattening and bevel shaping/general geometry. Hence, my bevels are flat. With the veritas guides, micro-bevels are easy, and no rounding issues (like those mentioned by Dereck) arise.
Nobody has mentioned the "scary sharp" method yet, which works great. I'm of the persuasion that whatever method works for you, whatever cuts the wood, that should be the one you use.
Just a thought.
Sam,
A hollow ground chisel creates a weaker edge for any given bevel angle than a flat or convex bevel. Convex bevels are the most advantageous structurally.
How much does it matter? I can't say. But I think the hollow ground edges get dull faster. Also- a semi related subject, highly polished edges are stronger and will thus last longer. Again, how much longer is a question I can't answer.
I grind everything flat or convex. If I can get away with a hollow grind, that tells me I could grind a lower angle flat or convex.
In general, I think lower angles are better. We've had this discussion recently as i recall.
To the OP, one advantage of the tormek type grinder you have is that the hollow grind it produces is slight. That's one advantage to larger wheels. My 22" grind stone creates .003" of hollow in an average chisel.
Adam
Interesting stuff, Adam.
A hollow ground chisel creates a weaker edge for any given bevel angle than a flat or convex bevel. Convex bevels are the most advantageous structurally.
I guess I can intuitively appreciate this at a certain level: there's more metal with flat or convex shaping behind the edge. But I think most of us use secondary bevels because of the process(quicker to hone) and materials (uses less metal and more slowly) efficiencies they bring. And when you've put a secondary bevel on, doesn't the "mass behind the edge" advantage kind of disappear. I tried to sketch this to help explain my thought process (see below) - the red dots being the actual dulling zone, so to speak. Once a secondary bevel is ground, the dulling takes place so far ahead of the start of that flat secondary bevel (the same secondary bevel you'd have on any other grind (flat or convex), by the way, that i just can't imagine a reason for a different result. In other words, why would the cutting edge "care" (strengthwise) whether well behind it the metal is slightly convex, concave, or flat. Does that make sense?
highly polished edges are stronger and will thus last longer.
This makes sense to me intuitively just because more polished means less friction (i.e., heat and wear).
Edited 12/19/2006 2:08 pm ET by Samson
- - - - Sarcasm alert (for our politically correct masters)
Yes,
And angels can dance on heads of pins.
End sarcasm alert - - - -
Hollow grinding confirs many demonstrable advantages to the sharpening process, not the least of which is that it facilitates rapid, very accurate honing by hand.
Why assert that hollow grinding weakens the edge or that hollow-ground edges get dull quicker when you admit in the same breath that you can't prove such to be the case?
Even a 6" wheel does not undercut the bevel that much, especially considering that honing the polished flat(s) reverses the undercut, as does applying a microbevel.
I would say that with the polished flats in place, and certainly with the microbevel, that the geometry of the cutting edge is the same whether the process started with hollow grinding or a flat bevel.
And even if a tool with hollow grinding does get dull faster (I don't think it does), the hollow grind makes rehoning so much easier, that bringing the edge back to sharp is more likely to be done. Meaning the tool has a sharp edge as much or more of the time than a flat ground version.
Now, back to the angels . . .
Rich
I belong to the school of thought that a hollow grind doesn't affect the strength of the edge since, as others have stated, and drawn, once the blade is honed there is a small to medium sized flat bevel behind the edge.
I use a small 5" to 6" wheel, on an old hand crank grinder, to grind my blades and then use small hand held diamond stones to do the final honing and resharpenings.
John White, Shop Manager, Fine Woodworking Magazine
"Why assert that hollow grinding weakens the edge or that hollow-ground edges get dull quicker when you admit in the same breath that you can't prove such to be the case?"I hear ya. I've been an engineer long enough to know that the world is a complicated place and sometimes things don't work the way they do in the computer models. On paper, what I said is correct. I don't know if it would make enough difference for you to see it in your shop. Well maybe I'm wrong. You probably could see it in some certain circumstances.....Here are my recommendations:
1) Never hollow grind your mortisers. There's little question in my mind analytically and empirically that this results in "pre-mature" edge degradation.
2) Consider honing the hollow out of or nearly out of your favorite dt chopping chisels. In my case that's my 6-9/16" firmers.Here's more of the science behind this:
The problem is stress caused by the blade going elastic. So it not so much a local phenomenon, but getting the stress out of the edge. That's why two chisels with the exact same bevel angle, one ground hollow, the other not, will behave differently. Remember that all steel is basically spring steel. It deflects in use.As for the polishing, the scratches are crack initiation sites. It really has nothing to do with friction. If you pull on two samples, one polished, one with grinder marks, the polished sample will break at a higher internal stress.Here's something else- The direction of the scratches is important. Scratches perpendicular to the edge are better.One more thing- all of these things have been known (but not necessarily understood) AND practiced for centuries. I had a nice chat with Leonard Lee about these things as well. Guess what- his little doohickies do everything I'm saying is good. You don't need a hollow grind to use one- in fact the grind becomes more or less irrelevant as a honing aid, the micro bevel makes the edge functionally convex, and the roller forces you to make the scratches go in the right direction. He's a pretty smart guy and very nice to answer my questions.I think woodworkers prefer simple absolute statements. Always flatten your chisel backs. Hollow grind your bevels. And I think guys do this without understanding why its important. And that's perfectly fine. Leonard Lee offers us a way to get higher performance without having to understand any of this and without having to spend years developing hand honing skill. I think that's a great service. I also think its a service to understand how this all works and why. Then you can decide when its important and when its not. You can call that counting angels on the head of a pin if you choose. Okay?Adam
Rich, and John WW,
Amen, and amen.
Ray
Hollow grinding and "scary sharp" aren't mutually exclusive. The hollow grind means less steel to sharpen, and it's a little easier to hold at a proper angle without a sharpening guide.
Try sharpening two chisels, one with and one without a hollow grind, and see which you prefer. Then you'll be an expert at your own preference...as hollow ground or not means diddly when it comes to tool use.
I've been using the Tormek for years. Simpley stated- It is awesome.
Like any tool- there are tips and tricks to getting the most out of it. (if you get one you should post back and ask for all the pointers).
If you are splitting atoms with your chisels- there might be a better system- if it is wood that you work- you'll be happy.
good luck
dave
MANY thanks to all who responded. I did try the New Jet slow speed grinder today and was impressed with the ease of use for doing chisels and just how sharp they turned out. I definitely prefer it over an 8" slow speed bench grinder. The Jets verrrry slow RPM sure prevents any aggressive grinding mistakes and keeping a truly square bevel was far too easy. Thanks to all again, There was much to chew on.Work Safe, Count to 10 when your done for the day !!
Bruce S.
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