No, it still acts like a wedge.Originally Posted by Todd Zucker
jtk
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No, it still acts like a wedge.
jtk
"A pessimist sees the difficulty in every opportunity; an optimist sees the opportunity in every difficulty."
- Sir Winston Churchill (1874-1965)
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Pat; you raised a very valid question. Who hollow grinds the backs of their western chisels and plane irons. And who would go to that trouble of hollow grinding the soles on their western metal bench planes. imo the smell of BS is not coming from your direction.
Stewie;
Contributor
I am not trying to weigh in here, but just trying to learn from the debate. The reason I am interested is that I have been intending to hollow grind my Western chisels on a Tormek for the first time, and I don’t want to screw things up.
Derek and others present an argument that I can grasp, that the hollow grind makes it faster to sharpen what would normally the primary bevel, but is in fact both the primary and secondary bevel. And easier to do freehand because it provides two reference points.
On the Japanese chisels, the hollow grind is not recommended, and a single bevel is suggested if IIRC. But I understood that the reason was not because of the geometry of the wedging action, but instead because there is less non-hardened steel to support the hard flat edge on a Japanese chisel, and it would chip.
The last point made, as I understood it (and might have misunderstood) was that the hollow grind would not make a proper wedge sufficient to shear off the fibers. I am thinking this is related somehow to the chipbreaker concept in the video I watched that explained why the chipbreaker’s placement close to the edge of the plane blade helps prevent tearout on difficult woods.
On a Western chisel with the exotic metals, though, if the hollow grind isn’t going to cause the chisel to chip, then it seems like it comes down to two other factors. The geometry of the blade and the forces they create (wedging action) and the properties of the wood.
In that case, it seems to me that if you have a hollow grind, the leading edge of the chisel (i.e., the wedge”) would have much less influence because it is much narrower than a single-bevel Japanese chisel. You would be able to steer the tool straight when paring or chopping more easily than with a Japanese (or mortising) chisel. That would be the case at least until you got deep enough into the wood for the far edge of the bevel to come into play. If you were paring straight into the grain, you might have problems with the tool following the grain of the wood instead of the direction you intend. But if cross grain paring or chopping, then it wouldn't be as much of a factor.
Am I way off base on this? Again, just trying to understand and learn, not debate.
Member
Narex now sells Western "dovetail chisels" with hollow-ground backs. I think they're sort of silly looking myself, but that's just me.
I don't know if this counts as a plane iron, but I've seen several low-angle spokeshave irons (most notably everything from WoodJoy) with hollow-ground backs. In that case the hollow grind serves a dual purpose: It makes the iron easier to sharpen and increases clearance just behind the cutting edge.
There's somebody out there who will try just about anything you can imagine. Patrick Leach tells a great story of "hollow grinding" of plane soles gone horribly awry. Start at the paragraph that begins "and now for something completely different", next to the picture.
Last edited by Patrick Chase; 02-20-2018 at 8:06 PM.
Contributor
A wedge is still a wedge. It will react pretty much the same whether it is hollow ground, flat ground or convex ground. It will have different reactions based on the bevel angle.In that case, it seems to me that if you have a hollow grind, the leading edge of the chisel (i.e., the wedge”) would have much less influence because it is much narrower than a single-bevel Japanese chisel.
Maybe someone who is good at the maths can break it down into a formula.
jtk
"A pessimist sees the difficulty in every opportunity; an optimist sees the opportunity in every difficulty."
- Sir Winston Churchill (1874-1965)
Contributor
How strange.....someone out there will spend "hours" to make the back of a blade "perfectly" flat......then turns around and wants to grind a "handi-grip" hollow into the perfectly flat surface......? Weird Science Project?
Contributor
Actually there is sense to hollowing the back of a Western blade. However this is only done under specific circumstances.
The circumstance is that the back of the blade is not flat and needs to be made flat. The example that comes to mind is when I needed to flatten the back of a drawknife. Grinding a slight hollow made it easier to do, and the hollow was lapped out anyway. I think that this is the point - that one is not seeking to create a hollow ala a Japanese blade, but remove the high points and speed up a flattening process. Note that this is not about polishing, which is a different area.
Regards from Perth
Derek
Last edited by Derek Cohen; 02-20-2018 at 10:29 PM. Reason: dyslecix
Contributor
I have never hollow ground a chisel blade because I've had no need. My chisels sharpen just fine. My Barr timber frame chisels are just the opposite, he recommends convex ground for strength.
I have had to concave grind my A2 BU plane blades so I can sharpen them before I die. I used to think I would like to use them but I've just replaced them all with BD 01 blades attached to different planes. Not entirely without some pain as the new blades are thicker but a huge improvement.
My 10" wet wheely thing can now usefully grind stainless steel edges to some useful purpose.
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Shakespeare wrote “Home-keeping youths have ever homely wits.”
There is a similar saying in Japanese that translates to “A frog in a well knows nothing of the wider world.”
BS meters require constant adjustment.
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“He has all the virtues I dislike and none of the vices I admire."
Winston S. Churchill, Wealth, War, and Wisdom
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Go ahead and put a hollow grind in the back of your chisel if you feel that its necessary. Just keep in mind the future when you have consumed the metal up to that hollow and try to figure out some fancy tapping out procedure to get metal back where you need it. Perhaps some of our experts could comment on the proper location and depth of this back hollow from their own tremendous experience / knowledge with doing so. I'll meanwhile stick to the basics thank you.
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Reminder to Everyone: keep it civil, please. This sounds like it can get personal quickly.
Contributor
Very little of my chopping uses the blade back as a reference. I typically only do this on the last chops of a mortise wall or when shearing off the waste which remains after coping between dovetails.
As Warren mentions, picture the chisel as a wedge. If you utilize the bevel to help in cutting, you will be shearing off a consistent portion of waste as the chisel is driven down into the work and out from the work. The work is used as support for the cutting action which pushes the waste away while shearing the fibers below it and splitting the waste out as it travels. Consider the section view of that waste, it forms a triangle for the first chop, and progressive chops are a consistent thickness section. After this is all removed and you are out to the baseline, what remains is a small interior ramp of waste. This can be chopped into with the bevel facing away from the work and it will be easily removed when clearing the floor of the work.
If you reverse the chisel and work with the bevel facing away from the work (and toward the waste) as you chop the wedging action will be driving the chisel toward the baseline of the work. It will attempting to shear an excavate an increasing large section of material. It is much harder on the work, harder on the chisel and harder on the user.
Bumbling forward into the unknown.
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Thank you, Brian. Very helpful.
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