Putting a "cove" in the bottom of my chisels. How?

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I figure most folks here have seen how them thar' high-falootin Japanese chisels have a concave bottom so that, when lapping the bottom, the only material you have to remove is on the perimeter... not in the middle. (If not, here's a pic:
http://www.benchworks.com.au/images/5%20Chisel%20Set.JPG )
Supposing that I wanted to have this nice feature on my existing, non-stratospherically-priced chisels, does anybody know any relatively easy way to achieve this? Perhaps with a conical grinding stone mounted in a drill-press?
Alternatively, does anybody have any tricks for automating the laping process? I've lapped a few of my chisels but, with the larger ones like the 1.25"... that's a lot of material to remove. It sure would be nice if there was some contraption that I could clamp my chisel and stone to and it would just grind them against each other for an hour while I went to get a sandwich. Anybody seen something like this, or shall I design one myself?
- Joe
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this. for a joiner's chisel you want the face flat, no? - otherwise it would be really tricky to use sometimes; and when you remove the bur you don't actually take off any steel from the flat side, you just bend the burr one way and then the other until it breaks off.
tim w
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Tim W wrote:

Less material to remove when you hone them, I figure.

Well, if you were in a situation where you couldn't rest both sides of the chisel against the workpiece (and were too stubborn to just reach over and grab a narrower chisel), then you'd have problems. However, as long as both sides of the face are touching the work, it doesn't matter if the material in the middle of the chisel is flat, coved, or *gone* completely.

True, but I'm trying to resurrect a couple of chisels that I wrecked early on in my woodworking days. I had some craftsman chisels and needed to get the milling-machine marks off of the face to get it nice and flat. "Hey, my belt-sander platen is flat! I'll just hold them against the sander while it's going!". So, I used my belt sander to sand the tool marks out. What I discovered too late was that the sanding belt wanted to ride a little above the platen (on a little cushion of air), so I was depressing the sanding belt just slightly when I'd press the chisel face against it (imagine placing your chisel against a mattress or pillow). This caused there to be more sanding force against the corners of the chisel and now the chisels have little "chamfers" or slight round-overs on the corners of the face.
Now, you're probably thinking: "You're trying to salvage a 'crapsman' chisel? C'mon! Just toss 'em and go buy another set... or go buy some *real* chisels!". Well, I *did* buy another set and I sharpened them properly the next time. But I still want to see if I can recover these... just in case I, someday, come across some *nice* chisels with the same problem at a yard-sale... or if I someday cause this problem to some of my nice chisels.
Think of it this way... this month's issue of FWW has an article about how to recover from joinery goofs. Think of my project as trying to discover how to easily recover from sharpening goofs.
- Joe
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snipped-for-privacy@emenaker.com wrote:

The blades are hollow-ground to make sharpening easier. An often-asked question is what to do when the blade is ground down so far that the hollow reaches the cutting edge. This is actually not a problem - regular sharpening and honing of the face moves the hollow back so that a straight edge is automatically maintained. In fact, overenthusiastic sharpening or grinding of the face by some users enlarges the flat between the edge and the hollow-ground part of the chisel.
--
Sir Benjamin Middlethwaite




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Fri, Sep 1, 2006, 12:04am (EDT+4) snipped-for-privacy@h.co.uk (The3rd Earl Of Derby) doth burble: <snip> This is actually not a problem - regular sharpening and honing ofthe face moves the hollow back so that a straight edge is automatically maintained. In fact, overenthusiastic sharpening or grinding of the face by some users enlarges the flat between the edge and the hollow-ground part of the chisel.
Where did you come up with that little tidbit? I don't think so Earl.
JOAT Justice was invented by the innocent. Mercy and lawyers were invented by the guilty.
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The3rd Earl Of Derby wrote:

They're not hollow-ground (on a good one anyway), they're forged that way.

Depends on whether they're ground, or they're forged. Either flatten them, or tap them out (read Toshio Odate for details).

No it doesn't.
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snipped-for-privacy@codesmiths.com wrote:

Yes it does
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Limey Lurker wrote:

What do you think the "face" of a chisel is ?
If you have a modern cheap Japanese chisel with a back hollowed by grinding, then occasional grinding of the _back_ will make this hollow shallower and will also move its edge away from the cutting edge. Working on the edge or face of the chisel though won't shift it.
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snipped-for-privacy@codesmiths.com wrote:

In this discussion, I've been considering the "face" to be the big, flat side of the chisel that that faces *away* from you when the chisel is in its retail package. It's the side opposite the one that has the bevel cut into it. It's the thing that has a hollow in it on Japanese chisels. It's the thing that sharpening articles tell you is just as important to have flat and smooth as the bevel.
It appears some people are calling this the "face" and others are calling it the "back". Norton Abrasives calls it the "back face", of all things.
To avoid any further confusion, I suggest that we drop the usage of both of those terms and henceforth refer to it as the "snorfl". :)

Agreed.... which I, believe, is what the other poster meant when they said:

...assuming that, when they said "face", they were referring to the snorfl.
- Joe
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OK now you are closer than you were when you started. Now all you need to do is to grind the center of the chisel to meet back with the corners. Use the fine wheel on your bench grinder. The closer you get to a sharp edge the greater the risk of getting too hot, have a can of water close by and quench often. When you get close to your desired geometry cheat a little and side wheel the chisel. This wil bting you flat. Now you have reestablished the proper geometry of the chisel and it is almost sharp now use your stone or diamond lap. Start with the rough and finish with the fine. In less than 10 minutes you will have a razor sharp chisel.
There is nothing wrong with a Craftsman wood chisel, if it is sharp it will do the job.
--

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Roger Shoaf

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I suppose I'm nit-picking here, but wouldn't this technically shorten the funtional lifespan of the chisel's back(maybe not in your lifetime), thus the chisel itself? And I sometimes(well, often) use the back to orient my stroke. Besides, once the back is polished, you hardly need to touch it again. You can probably save more time in your sharpening by hollow grinding the bevels, then only lapping and polishing the very tip and heel of the bevel, instead of the whole thing. I think. Tom snipped-for-privacy@emenaker.com wrote:

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snipped-for-privacy@emenaker.com wrote:

Japanese chisels are laminated steel. The back is the harder steel which is forged with the softer body steel to have that depression. The Japanese chisels have to have the hollowed back and harder steel beaten out to form a straight edge as the chisel shortens due to repeated sharpening.
Your econo-chisels aren't laminated so you won't have the issue with the harder steel, but you will still have to deal with that depression which is in a steel that is, on average, harder than the bulk of the Japanese chisel's body. In other words, a pain.

I'm not sure how much lapping you'd actually have to do once you've done the initial lapping. You certainly don't have to lap the entire back every time you sharpen the edge.
It's tough work to make a cheap tool pretend it is an expensive one. Usually more work than it's worth. You can get used Japanese chisels on eBay and even some of the new ones are surprisingly reasonably priced.
R
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RicodJour wrote:

Old and high quality Japanese chisels are laminated with a thin steel layer and the hollow is forged in. More recent and cheaper ones are still laminated, but with a thicker lamination and with the hollow ground in.
You tap out the thin lamination ones, you grind out the thick lamination ones. If you try to tap out a thick lamination one, you'll crack it.
Really nasty Japanese chisels are made in China and aren't laminated. Apart from specialist ones, I've never seen a Japanese-made bench chisel that wasn't laminated (i.e. they just don't cut that corner in manufacturing).

Those "econo chisels" are Iyori, so they're really pretty decent quality. Thick laminations, so grind the backs flat as needed.
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snipped-for-privacy@codesmiths.com wrote:

That makes sense from the physics standpoint, but I've never heard of a Japanese chisel whose laminatied steel was so thick it couldn't be tapped out. Can you point me in the direction of some of those chisels? I want to see what's what.

The econon-chisels was referring to the OP's wish to resurrect some cheap chisels. He posted the picture of the Iyori chisels as an example of what he wished to do with the cheap chisels.
R
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RicodJour wrote:

Iyoroi. I think David Charlesworth has written on this (he was the first person I saw who was grinding out his chisels, not tapping them).

Ah - I came into this thread partway through. I see no point in adding a ground hollow to an existing chisel.
I _might_ try this on a 2" wide slick I use for cleaning up mortices in larch timber framing. I do sometimes get trouble with resin stickiness on fresh green larch.
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snipped-for-privacy@codesmiths.com wrote:

I emailed a temple-builidng acquaintance in Japan about the lamination thickness and this was his reply: "Hello sir. Thank you for your Q. Thick steel is bad! Because steel is thin, I can bend it. I do it like a bimetal and bend it. I tap a soft iron and grow volume. I do not tap steel and do not grow it. Steel is bent by pushing gently below as a result that soft iron lengthened. We must keep big back hollow as newer article. Because I must tap soft iron. Imagine Ski bord and figure skating shoose. Do you understand? Both of side end mirrored back hollow must become ruler. We call 'ashi'
means leg. We love thin women's leg ,don't you? We must keep thin leg (ASHI). I will write about them on Ebay guide. Please wait for a while. I hate thick steel. Exported Japanese tools must make thick steel. Because ,many foreign owners sharpen back many times... You know ,Steel will be lost!!! Japanese chiselsmiths change thickness by a customer. All of my blades are very thin. Regards "
Can you see why I love this guy?
R
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Mon, Sep 4, 2006, 5:36am (EDT-3) snipped-for-privacy@codesmiths.com doth ponder: <sniup> I _might_ try this on a 2" wide slick I use for cleaning upmortices in larch timber framing. I do sometimes get trouble with resin stickiness on fresh green larch.
Hmm, at first thought I would think maybe dipping the slick in mineral oil, kerosene, recycled cooking oil, alcohol (hopefully not the drinking kind), or something might do the trick.
On the other hand, I also wonder if cutting a slot clear thru the slick would work - at the risk of ruining the slick, of course - but it is your slick, so it's not my risk. LOL
Might want to consider making one, or a few, for test purposes. I betcha the old timey shipbuilders had the same problem, wonder how they dealt with it.
JOAT My shop, my rules.
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First off unless you have been using a wood chisel as a nail cutter or a stone chipper then lapping should be relativly easy, and if the chisel has been abused, dressing it with a grinder or a belt sander is the quick way to get close enough.
Once the angle has been established it is really no big deal to bring out a razor sharp edge. I like the diamond stones they have out now, they cut real fast.
They do make a chisel sharpening guide, but I have never found a need for it.
Once I get the edge sharp enough to shave hairs off my arm, I will take it to the buffer and polish it. I am not sure that it makes it cut any better but it sure looks nice.
--

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Roger Shoaf

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Roger Shoaf wrote:

I don't do that for looks, I do it to save time. Takes longer to chase the wire edge than to simply knock it off with two passes over a wheel loaded with green compound. It also makes the chisel almost immune to rusting. Not sure if that's from the polished surface or if it's because the compound leaves a light grease film.
Do you rake your wheel? I don't, and its stropping action seems to improve with each use.
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At the shop I worked at we only had one buff wheel and that saw a variety of materials and compounds so it was cleared from time to time especially if I was buffing something with progressively finer compounds.
I suspect the wax base in the buffing compound is what is inhibiting the rust.
--
Roger Shoaf
If you are not part of the solution, you are not dissolved in the solvent.
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