Mortise chisel sharpening considerations

[Skip J.]

Friends, family, and aquaintances are amazed when I tell them that I'm a "self taught" woodworker.

But, in truth, I just read and asked questions on this forum for years.

I've also met some of my best friends on this forum.

Good people here!

Well said Peter, well said indeed....

[Alan S]

Ideal tool prep depends on both stock and technique.

Derek's methods as usual are well thought out. However the woods he works with are Australian, and mostly harder than domestic species in the USA. Why does this matter? Because here we may be able to drive the chisel deeper into the stock. With a narrow 20 degree primary bevel, the chisel can get stuck.

If you sharpen at 30-35 degrees without a secondary bevel, or only a very slight one to focus work on the edge without changing the angle much, that extra metal helps to break off and push stock to the side more effectively as you chop, making it more easily removed. In much harder wood, that may not be possible.

In other words, with some types of wood, and some procedures that seem to work pretty well, you may not want such a narrow primary bevel.

[Bibliophile 13]

You've been given good advice here.

You should need to flatten only about an inch of the back. You don't need the whole back flat--just whatever normally touches the sharpening stone when you hone. That can actually be a very short length on a chisel, but about an inch is usually practical.

Once you flatten the back, the lands should be nice and crisp, if not sharp. Those crisp lands will help scrape the inside of the mortise as you lever the waste out of the mortise. If the mortise chisel is trapezoidal in cross-section (rather than square), that's a plus. It won't get stuck in the mortise nearly as easily. Either way, I would not touch the sides of the chisel unless absolutely necessary. Mortise chisels are the one kind of chisel that really should be kept in standard widths because they sometimes need to combine with other tools (like the plow plane) that also come in standard widths. There are simple work-arounds if you really do need to take a little meat off the sides of the chisel--say, if there is deep pitting--but in general you should just have to hone the bevel and the back.

As to the exact bevel, you may need to experiment somewhat until you find what works for you and for your tools. You've been given a good range of possible bevel angles, and all of them will likely work. There may, however, be an ideal bevel angle that is suited for the kind of steel in your chisel and the kind of wood you often chop mortises in. All mortise chisels work best with a shallow primary bevel and a generous secondary bevel. Beyond that, there is some range of workable bevel angles. If you find your edge failing too quickly, try a steeper bevel. If you find the chisel just isn't penetrating, try a shallower angle. Different steels seem to like (or tolerate) slightly different angles, so don't be afraid to experiment. And don't get discouraged if your first attempt gets less-than-premium results.

But if what you try first works well, then just keep doing it. This isn't an issue to over-analyze.