Sharpening Mortise, Sash Mortise Chisels

[Jared McMahon]

I have a couple English style mortise chisels and a sash mortise chisel that are in solid shape but badly need sharpening. Two of them in particular are rather rounded on their bevels, with a good number of micro-bevels. This is making it a royal pain to re-establish a true primary bevel by hand, they keep rocking and I'm simply continuing the rounding process. I tried my Kell honing guide but the bevels are too long for the rollers to accommodate.

Any suggestions as to what I should try next? I have a grinder but I'm reluctant to use it on them. I recently found out how easy it is to blue a blade (thankfully not on anything I cared about).

Jared

[Andrae Covington]

I don't have any advice, but I feel your pain. I normally use a guide (Veritas Mk2) but the mortise chisels won't fit, so I've had to freehand them. I'm sure everyone who always freehand sharpens their chisels is just shaking their heads at a "training wheels" guy, but I don't care. nyah nyah nyah I can't hear you. Anyway a few months ago I chipped the edge of one while pounding through white oak. That was about the time I wished I had a bench grinder. It's still not back to what it should be, but I've put off dealing with it until the next time I need it...

[Adam Cherubini]

Ny opinion is, guys aren't using their noodles when it comes to antique mortise chisels. First, there's the assumption that everything we get needs to be "restored". Maybe your chisels are fine as they are? Why not try honing the bevel you've got? Chances are, there's a reason somebody rounded the bevel of that tool (that's the way I hone them too). Just because someone is dead now, doesn't mean they were stupid when they were alive.

Second, guys are treating these tools like crow bars.The problem is so bad, no "normal" steels will hold up to the abuse. Yet the antique chisels are still available, long, straight, etc. We know guys chopped a lot more mortises in the past than we do now. So how do we reconcile this?

My advice is to maintain a gentle curve to the bevel of your mortises. A curved (convex) bevel is stronger than a concave one. Hone the last 3/16" of the edge to 30-35 degrees. Try to stick with whatever is there since that craftsman probably already found the angle needed for that chisel.

Next, be careful and craftsmanly with your mortise chisels. You can pry loose chunks with it. But remember that it IS a chisel. It cuts the wood. Don't be too rough with it (prying especially). I have mortisers with their original beech handles intact after 200 years. They are clearly used and have been honed thousands of times. But the don't appear abused. Our ancestors are trying to teach us something. Listen carefully. DOn't change what you see until you fully understand what they are trying to tell you.

Lastly, don't make the mistake I made and insist that the backs be flat. They don't actually need to be flat to function. In fact, I can argue that a curved back is actually beneficial for chopping.

Good luck with your mortisers. I haven't used Joel's Illes chisels enough to compare, so those aside, I think antique mortisers offer the best performance and the best price. Remember they are a limited resource.

Adam

[Tim Sgrazzutti]

+1 on what Adam said. My vintage OBMC's were found with slightly convex primary bevels, which I've maintained the shape of. I have had to rework some of the primarys, as the secondarys were getting too large. Given the 20-25 degree primary angle and the thickness of the chisel, this requires removing a LOT of metal, which I certainly don't want to do by hand. I used a grinder, holding the chisel perpendicular to the wheel (you definately do NOT want a hollow grind) and rotating the bevel into it. After it was close, I finished it up using the same technique on a 1" belt sander, but that could also be done on stones.

You don't need to work all the way to the edge doing this, which really helps avoiding burning the steel. I stopped when the secondary bevel shrunk from about 3/16's to 1/16th. Then, hone the secondary in the 30-35 degree range and you're good to go. Keeping the secondary small makes touch ups easy since there's little metal to remove.

[John Coloccia]

A lot of the old timers made a slightly convex primary on mortise chisels because it makes it a little easier to pry. My old pig stickers came like that too. There was a large, flat, secondary bevel on it....maybe 1/8". I continued that with a tertiary bevel. To me it looked like it was intentionally rounded, then a secondary was made, and then the tertiary, really dividing the bevel into two parts....the chopping edge and the prying fulcrum. It worked really well.

Shucks, as long as it chops mortises, it's all good.

[Terry Beadle]

A couple of probably obvious suggestions regarding the use of your grinder and avoiding blue-ing the edge.

I have a slow speed grinder ( 1750 rpm ) and you have to work a bit to get it to blue an edge so I'm going to "assume" that you have the 3000 +rpm style.

First you don't need to grind all the way to the tip of the chisel edge. You are just trying to re-establish the primary bevel. The final 1/32 to 1/8 th inch of the bevel should be established by stones or scary sharp methods. Use very little pressure on the chisel while using the grinder. Let the chisel almost bump along. Use the grinder about 5 seconds and then plunge the chisel into a can of water for 15 seconds. That should keep the blueing from happening.

Also consider that these are mortising chisels and probably could use a 35 degree primary bevel. Some do 30 with a 35 micro which is also good. I like the primary bevel to be the only bevel on a mortising chisel. I also like the primary bevel to be flat and the back as well. This is how Japanese chisels are set up and they take little time to maintain the flat bevel and back.

Once you have established the majority of the primary bevel on the chisel, use the stones to put the final 1/32 to 1/8th inch cutting edge. This should be fairly quick on a freshly ground chisel as it will have a ice skate blade like two places it first touches on the flat stone surface. Later after maintaining the flat primary bevel, it may take a bit more time to re-establish a good working edge but it's not that bad.

As far as the rounding of a primary bevel, I've seen recommendations on pig stickers to round the upper end of the primary bevel only. This aids in the levering out of the chips but it's not essential but a optional improvement to the pivot point of the levering. IMO you should not let the primary bevel get a rounding crown near the cutting end. This usually occurs from hand sharpening practices that don't use jigs to maintain the bevel on the stone dead flat. It works but it's not the ideal to me. I think the resistance in the wood when it comes off a micro bevel when it hits any rounded crown is not ideal. To me it's like a speed bump. I don't like them.

It's the kind of wood your are cutting the mortise into that dictates the primary bevel angle. Soft woods can allow for primary bevels at about 23 to 27 degrees and hard woods should start at about 30. I've found that 35 keeps a good edge a long time on my mortise chisels or a bench chisel if I'm using it instead as I don't have a full complement of mortise chisels.

Don't be afraid to experiment with your chisels as they are a wonderful tool and the better you keep them tuned to the wood your are working the more enjoyable the process and results will be.

If the above is already some things you've been doing, then yahoo! ...and you can ignor the suggestions given.

Enjoy the shavings!

[Frank Drew]

I like a flat bevel; I think a curved bevel is more work when chopping, there's more resitance when going through the wood.

And how can you chop straight with a curved back to the chisel?

[John Coloccia]

My back was straight. The primary (convex) bevel was something like 20 or 25 degrees, with a secondary at about 35 degrees. The low primary bevel allows you to go fairly deep, even with the little convex curve on it. I'm not saying this is the right way or the wrong way, only that mine was like that and worked very well, and I've seen enough old ones that are like that to think they were doing it for a good reason.

[Frank Drew]

John

I should have included a quote; I was questioning this comment.

Lastly, don't make the mistake I made and insist that the backs be flat. They don't actually need to be flat to function. In fact, I can argue that a curved back is actually beneficial for chopping.

[Andrae Covington]

...My advice is to maintain a gentle curve to the bevel of your mortises.
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I haven't used Joel's Illes chisels enough to compare, so those aside, I think antique mortisers offer the best performance and the best price.

I have the Ray Iles from TFWW. On the website Joel also recommends rounding the primary bevel, but since not everyone likes that they decided to have Ray make them flat, figuring it's easier to add if you want it vs trying to take it away if you don't.

As far as the chipping on my chisel, I don't think I was being unduly rough in how I was using it. Most likely the heat treating process made the tip more brittle than usual. As I understand it, the chromium content of D2 steel has a tendency towards brittleness (especially at low angles, which is why a fairly steep secondary bevel is recommended). After grinding back to reestablish the secondary bevel, it probably won't chip like that again.

[Jared McMahon]

Thanks for the advice, all. And rest assured I don't intend to square off any of the major curves in the chisels. My main concern is that, after a while trying to free-hand the sash-mortise chisel, I had added a few more mini-bevels and had begun to skew the cutting edge. That's the point where I decided to stop and make sure I wasn't doing/overlooking anything braindead. I'm gonna guess I need three things: practice, practice, and practice.

Btw, I haven't tackled the mortise chisels yet. The 1/4" suffers from a bit of the same many-bevelled issue but it's not bad. The 5/8" had a big nick that I had to take out, so I'll have to completely re-establish its primary.

For the curious, Witherby 1/4", Stormont 1/4", Brades 5/8".

[Mike Henderson]

I've bought a number of old pigstickers. I like a 25* primary so the bevel is out of the way, with a much steeper secondary, maybe 35*, so the edge will hold up. I established the primary on a power grinder, being careful not to overheat the edge. That's actually easier than you may think because you're mainly getting the primary bevel to the angle you want. The fine work on the edge will be done on a stone when you do the secondary bevel.

Mike

[Adam Cherubini]

I like a flat bevel; I think a curved bevel is more work when chopping, there's more resitance when going through the wood.

And how can you chop straight with a curved back to the chisel?

Hi Frank,

This is tough to describe, but I'll give it a try. If you don't buy it, I could show you and you'd probably see what I mean even if you prefer not to adopt what I'm saying.

First, the curved bevel isn't really different than a secondary bevel. The edge that cuts the wood is a greater angle than all that follows. Of course, this is not the case with a straight bevel. So the concave or convex bevels actually have less contact than a straight bevel.

Second, the wood doesn't care that your chisel's back is flat nor does it care that you'd like a straight cut. All it sees is a wedge. When you push down on a regular chisel, the wood pushes on both sides (equally if you aren't paring). This pushes the edge sideways, ruining it. Better would be a chisel beveled on both sides (and this sort of chisel was common 500 years ago and for at least 1000 years prior to that).

You can prove it to your self by holding any chisel straight and tapping it into the wood. The handle will want to move forward on each chop (fwd toward the beveled side). Actually if you hold your chisel perfectly straight and chop straight down, you'll under cut your line. What guys really do without thinking about it is they pull the chisel handle back as they chop.

Paring isn't entirely different. You'd think you could hold a flat back flat against the wood and slide the tool around to take off high spots. You can do this somewhat. But once the tool starts to cut, the pressure from the cut wood tries to force the chisel edge down.

The trick is just to remember that regardless of what we think or want, the wood has it's own desires. Another example is sawing. We want the slit to grow, for the saw to go down into the wood. But saws don't actually cut wood like that. But that doesn't stop us from trying to push the saw down into the wood.

Adam

[Pam Niedermayer]

Prying is certainly a chisel breaker and completely unnecessary. You may want to take a look at Jeff Gorman's page on mortising technique (http://www.amgron.clara.net/maynardmortise40.html) and possibly his whole section on mortising (http://www.amgron.clara.net/mandtindex7.html).

Pam

[Deane Allinson]

I have several bolstered mortise chisels. Chopping mortises is probably my favorite task. I just tend to leave them alone. I like the look of a 30* but I have a couple a little shallower and find no real difference in performance on hardwood. I don't spend a lot of time sharpening either. I find that razor sharp is a waste of my time, but then I'm a serious whacker. It may be because they are laminated steel and the healthy bevel backs the edge up, but I can really pry out big chunks with out much if any chipping. My opinion is....there is really not to much to finesse on them that makes a lot of difference.
Deane