Sharpening Mortise chisels?

[Scoly2803]

Tried with sandpaper and a glass plate but it took so long.
Decided to try it on a low speed wet grinder (used the chisel that came with my morticer). After less than a minute I had what appeared to be clean, flat, smooth edges. Went very slo trying to keep the edges flat against the stone and just getting to the tips. Used the leather wheel with paste to lap and it got rid of all the grinding marks. Any thoughts on using the wet grinder for sharpening? Good/bad?
Now I need to get the inside edges. Found some cone shaped grinding stones but they are not specifically for mortise chisels. Am guessing that that is not important as long as they intersect with the very edge of the chisel since what I want is to just knock off the burr. Correct?
If the grinder is adviseable what other ways are being used?
Thanks
Steve

[Tom Miller]

What grit sandpaper? Were these chisels in really bad shape when you got them? When you buy them new, they're usually in very good shape.

I don't think you'd want to use anything but a flat surface abrasive -- not the curved surface of a grinder wheel, if that's what you mean. The sides of the mortise chisel should be flat and exactly in plane with the direction of motion. The sides should be perfectly perpendicular to each other.

For honing the inside, I got something like this at Rockler:





Actually, the one I got has two grits -- not sure how necessary that is.

Regards,
Tom

[LCHIEN]

What grit sandpaper? Were these chisels in really bad shape when you got them? When you buy them new, they're usually in very good shape.

I don't think you'd want to use anything but a flat surface abrasive -- not the curved surface of a grinder wheel, if that's what you mean. The sides of the mortise chisel should be flat and exactly in plane with the direction of motion. The sides should be perfectly perpendicular to each other.

For honing the inside, I got something like this at Rockler:





Actually, the one I got has two grits -- not sure how necessary that is.

Regards,
Tom

My understanding of mortising chisels is you're only supposed to grind the inside, not the outside, as with the tool shown above. That way the sides stay flat, square to each other and properly sized.

[Tom Miller]

My understanding of mortising chisels is you're only supposed to grind the inside, not the outside, as with the tool shown above. That way the sides stay flat, square to each other and properly sized.

That's right. I'm not suggesting grinding, but rather lapping, like you would the back side of a plane blade. I think mortise chisels benefit greatly from that.

But, it seems like the OP has some particularly nasty starting surface, whereas you shouldn't need anything coarser than 600 grit or higher for lapping the sides.

To OP, do you have any pics of what you're working with?

Regards,
Tom

[Scoly2803]

Sounds like my idea was not so good. Afraid of that.
Will go back to the glass plate and sandpaper.
The chisels were acumulating a lot of pitch buildup on the flat edges. They show grinding marks and based on the rub marks left by the wood after a few passes are not flat. Portions of the surface is shiney after using while others portions do not seem to have rubbed the wood at all.
Sandpaper grit I tried was 1000. What do you recommend. Do I have to go through several grits?
Thanks for the quick responses.
Steve

[Tom Miller]

Sandpaper grit I tried was 1000. What do you recommend. Do I have to go through several grits?

Well, if the surfaces are as bad as they sound (i.e. bad enough that you wanted to use your grinder), you might need to start with 320. If it appears that will take a long time, you might consider starting over with a new chisel. Just like the back of a bench chisel or plane blade, these surfaces should be lapped nearly shiny (>600 grit), and re-lapped every time you sharpen the inner bevel. Then, with a waxing, they shouldn't ever be picking up any contamination in the first place.

The good news is, you may be in for a very nice surprise with how well a good chisel works!

Regards,
Tom

[Scoly2803]

Will go that direction. Thanks for all the help.
Steve

[cabinetman]

The cone shape hone is for the inside bevels, which can't be dressed with anything flat. The outside surfaces I dress with 800x - 1000x silicon carbide, wet-or-dry, or the fine flat diamond hones (like nail files), both used flat, just to clean burs.
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