sharpening a mortice chisel

[engineer one]

as someone who uses his tormek quite a lot to earn the extra few quid from my local chippies, i find that when you first start using the machine it can chatter, that is to do with the way in which you hold the chisel, as well as the height at which you support it.

however the first thing to do is to use the diamond gauge and cut the stone back to ensure that it is round and the surface is properly cut back.
i must say that that to me is the most difficult part of owning the tormek, using the diamond hone on it.

next i have checked the stanley mortise chisel that i bought to experiment with, and although it has a slightly concave edge, i only sharpened it a short distance so the curve is not really relevant.

so my advice would be that you try to set the blade up so that only a short portion of it is on the stone, and that is as near as possible to being at top dead centre of the stone. then using the jig set it up so that the support arm is as low as possible. in this way you will i feel answer many of your problems in using the tormek on this kind of chisel.

another reason for the judder i feel is that too many people use too much pressure to try and sharpen. i only ever use the fine finish on the wheel whether i am doing new chisels which have to be first time fettled, or older ones which need rescuing.

i can sharpen and hone about 7 badly chipped chisels (normal ) type within less than an hour, and then i do not seem them again for weeks.

finally, as for using the side of the wheel, i think for cleaning up the back of a plane blade it has some value, but too often with a chisel you seem to get a really big line, and it is difficult to do what geoff brown does.
maybe when i have had as much practice. also it is easy to dig into the side, and maybe either cause damage to the wheel, or cause the mounting nut to come loose, both of which have happened to me.

final thought, what angle are you trying to grind, i found that using a slightly lower one, on the mortise chisel gave me better results for digging out.

hope this helps
paul :wink:

 

[Argus]

Yep, a little convexity is a Good Thing in a mortise chisel it seems. Somewhere I read claims that it helps "pop the chips free", which perhaps it does. Concave becomes an issue when you're prying away with a mortise chisel as regards strength, so not a good idea, while convex gives you plenty of strength. In short, forget the Tormek for this one.

Cheers, Alf

I agree with Alf on the subject of convex profile on a mortise chisel; regrettably, they seem to have dropped out of favour altogether since electric routers turned up.

My understanding of the geometry of these chisels is that they are irregular in all directions; the sides of the chisel stock on old mortise chisels tapers slightly toward the handle – a feature that is mostly missing in modern plastic-handle horrors. This avoids the sides binding in deep excavations. Repeat sharpening reduces the width of the mortise by a tiny amount over the years.
The convex curve, to my reasoning, provides lateral thrust to the chip, as Alf pointed out, plus the ability to withstand a considerable amount of hammering. Another point in the favour of an outward curve is that the cutting angle is not critical and quick honing can be done without having to worry about preserving exact angles. It's not necessary at all with this type of chisel that is intent on producing an accurate hole as quickly as possible.

If you can still get it these days, Jim Kingshott produced a video on chopping mortises by hand that explained how quick and easy it is to chop them out by hand, including the basics of setting up a mortise chisel.

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