Regrinding abused mortise chisels?

[Clayton Lambert]

A friend gave me some nice old marples/sorby mortise chisels. Problem is, somebody got to them with a grinder and really did a number on the bevel. Does a hollow ground cause the blade to get dull quicker?

If so- I'm no stranger to sharpening bench chisels, plane blades and gouges-- but mortise chisels have so much material to take of I cant fathom a way of getting a flat, non hollowed bevel without spending ten years on my diamond stones.

Is it time to invest in a belt sander?
What is the ideal bevel angle for these guys to do their magic?

289297

[Warren Mickley]

The ideal bevel angle is 30 to 32 degrees. Your chisels are not very far off. The upper right and the lower left chisels look the best.

[Greg Portland]

I have a few with a hollow grind (slightly less than the bottom one in the pic) and haven't had any problems. As long as the angle is OK @ the tip then longevity should not be a concern (assuming they didn't screw up the temper when the ground it the first time).

[Tom M King]

Looks like a good chance to find out how different bevels work on mortising chisels. Sharpen them up, and let us know.

[lowell holmes]

An old honing jig and a belt sander will make short work of reshaping the bevel. Be careful not to overheat the steel. After flattening the bevel, the honing doesn't take long.

Put the belt sander upside down in a vise and let the wheel on the honing guide run on the belt while presenting the flat on the bevel to the running belt. Watch your fingers when doing this.

[Derek Cohen]

Hi Clayton

I am in mind of Rob Cosman, in a video on morticing, preparing LN sash mortice chisels by hollow grinding at 30 degrees. This angle/method appears to have held up fine for him. My English Oval Bolstered mortice chisels are prepared differently, with a 20 degree primary bevel and a 35 degree rounded secondary bevel.

Regards from Perth

Derek

[Mike Holbrook]

I bought a roughly 5/8" Japanese mortise chisel at an auction site. One corner was broken off when it arrived, a sizable chunk missing. I did most of the reshaping with a DMT Dia-Flat diamond lapping plate that I was eager to experiment with. It took quite a while, several sessions, but it did the job. I think the belt sander or Tormek would have been a better choice and I am working with both on my drawknife collection, trying to improve my ability to create the edge shapes I want.

[Jim Matthews]

I would just freehand these on a coarse India or Diamond stone.

They look to be pretty close to what I'm after for mortising.
I too, like a convex bevel on my chisels and plane blades,
it only takes a few iterations to have a nice
continous bevel when you start from a hollow grind.

If these are good Sheffield steel, it won't take forever.

If you want to quantify the process, measure the current flats
and hone as normal. The difference in the flats afterward
will give you some idea of your progress.