Best way to approach new bevel?

[Steven Mikes]

I just bought a trio of mortise chisels from a fine gentleman in Ashby, MA. They need a little work to bring into top form again, but not too much. The part that's giving me pause is how to go about putting a new main bevel on the largest one? I have a bench grinder with 8" wheel, is that good enough? the resulting bevel would not be flat, is that an issue? should I get it close with the grinder then finish by hand on a 400grit diamond stone? Any other suggestions? Thanks in advance!

[William Fretwell]

Grinder and diamond stone seems the simplest. If it’s not a wet grinder proceed very slowly so you don’t overheat the steel.
The other thread on those chisels just brought back to life will be worth reading, especially the back bevel part.

[Derek Cohen]

Steven, I would avoid a hollow grind on a mortice chisel as the resulting edge may be too weak when prying to resist chipping. I prefer a flat primary grind at 25 degrees and then a rounded 35 degree secondary bevel. This is one of the few occasions I sharpen using Paul Seller's method ...

Start low and lift to 35 degrees ...

https://i.postimg.cc/rpY9392H/Honingmorticechisel1-zpsad015f6a.jpg

I used a visual guide when I started out ...

https://i.postimg.cc/QMMbfyw5/813b297c-6daf-4708-baad-279e19ce4d58-zpshjiiywbe.jpg

https://i.postimg.cc/ZRBLSyT5/mortice-guide2-zpsmrald6b3.jpg

Regards from Perth

Derek

[David Eisenhauer]

Using a bench grinder (6", 8") is one common way to establish a primary bevel of 25 deg on the mortise chisel, then use stones (diamond, water, ceramic, oil, etc) to create a secondary or micro bevel of approx. 35 deg (or whatever you prefer) on the tip end of the chisel. The curved bevel face of the chisel, resulting from using a grinding wheel to establish the primary bevel, is of no issue and actually can speed up subsequent stone sharpening sessions by having less metal to remove from the tip end only rather than a whole flat bevel face. Other folks don't use a grinder wheel for the primary bevel and do it all with stones. Both methods will definitely get you there and there are lots and lots of discussions on both methods archived on this forum. I will say that perhaps using a 400 grit diamond stone for the final bevel finish may be considered too rough for many here to use, but I am not very conversant with diamond grits vs oil and water stone grits and may be off base. I typically use a 6,000 grit and then a 13,000 grit water stone to finish my mortise chisels off with after establishing the primary bevel with either a grinder or by hand with a 800-1,000 grit stone.

[Steven Mikes]

Thanks for the replies! Here's what I'm thinking:
In this sketch, the black lines represent existing chisel shape.
Red is the desired bevel.
Light blue shaded region is material removed by hand.

If I do by hand only, that would be the top version in the sketch.
If I use the grinder to remove the reddish region in the bottom version, then there is a
much smaller amount of blue material left to be removed by hand.

[Warren Mickley]

Yes, you are doing the right thing, Steven. You want to end up with a flat bevel at around 30 degrees or maybe slightly higher. As other suggested a hollow is somewhat more vulnerable and a little awkward; we ride the bevel for most mortising cuts. There should be no secondary bevel. You could get away with a very slight depression in the middle of the bevel.

[Jim Koepke]

This is one of the few occasions I sharpen using Paul Seller's method ...

+1 on Derek's comment. A mortise chisel is one edged tool that seems to work better with a convex bevel. It seems to help clear chips better than a flat or concave bevel.

jtk

[Mike Cornwall]

It’s my understanding that the old craftsmen generally owned one mortise chisel and used that size mortise in their work. Buying chisels is fun, fixating on getting them in shape is fun, making a nice case for them to hang in is fun. But unless you need that chisel for a certain mortise already, it might be good to set it aside and spend some time with the ones that are closer to being functional. Might turn out that two is already one (or even two) more than you end up needing.
To quote my old friend Jonny, “that’s gonna look great on a shelf, man!”