This has not gone well...

[NZStu]

Old Spear and Jackson laminated mortice chisel + Oak = Oh dear :(

It started with delaminating, which seems to have removed much of the support for the hard steel layer. I figured I might as well press on and finish the mortice before dealing with it, but the tip snapped. Oops.

I should be able to grind it back, but that is a fair whack of material to remove. had originally ground it with a big 25 degree primary bevel, with about a 30 degree secondary. Would I be best to revise that?

[Scribbly Gum]

Old Spear and Jackson laminated mortice chisel + Oak = Oh dear :(

It started with delaminating, which seems to have removed much of the support for the hard steel layer. I figured I might as well press on and finish the mortice before dealing with it, but the tip snapped. Oops.

I should be able to grind it back, but that is a fair whack of material to remove. had originally ground it with a big 25 degree primary bevel, with about a 30 degree secondary. Would I be best to revise that?

That's very bad luck Stu. Nice looking chisel too.
Probably was bound to happen with that 25 degree bevel though. You can see that the first part of the brittle cutting steel is not supported by the softer and more flexible steel backing at the point
I think that most morticing chisels are ground around 30 degrees to avoid that kind of breakage in tough woods. Also it seems a straight 30 degrees with no secondary bevel is quite common. Hollow grinding can weaken the point in mortice chisels so I would try to keep the bevel straight if possible.
Happy grindings
SG

PS
I've just had another look at the second pic.
I would try grinding along the line from the start of the bevel down to where the break happened. Not sure what kind of angle that is, but that kind of blade needs more support for the laminated edge in harder woods. Even if it is 35 degrees it should work.

[Berlin]

Where's the heavy sigh emoticon...?

Mortice Chisel Pusher on the block.
You know where I am Stu. Don't be a stranger. I've got some sweet hook ups :;:Smoker:

But honestly, that sux, I hate to see a nice tool in pain.

[NZStu]

Where's the heavy sigh emoticon...?

Mortice Chisel Pusher on the block.
You know where I am Stu. Don't be a stranger. I've got some sweet hook ups :;:Smoker:

But honestly, that sux, I hate to see a nice tool in pain.

I wondered how long it would take for you to turn up!! :D


Cheers for the advice SG - I'll try that tack. You're definitely right that the hard steel needs more support than it had at 25 deg.

[NZStu]

After a marathon grinding session, my chisel is now about 7-8mm shorter, and has a single straight bevel at about 31 degrees. That should hopefully do the trick.

Bit of a PITA, but that's how you learn! I now know that old laminated mortice chisels need to be ground at 30+ degrees...

Interesting exercise though - there are slag inclusions in the backing steel, which makes me wonder if this one is actually fairly old.

[Basilg]

Stu

Your original bevels are the traditional way of sharpening Mortice Chisels, as the shallow angle allowed the chisel to take a deeper cut and cut the mortice quicker. I suspect that the problem is defects in the laminating of the two steels. this also indicates to me that it is a fairly old chisel as western tools were laminated when tool steels were much more expensive to produce, as a means of reducing the cost of the tool.

regards

[Artesano]

http://www.fine-tools.com/mukoumachinomi309540a.jpg
As we are talking laminated blades , I thought the Japanese should know something about it -quick search , and no surprise - they grind at 40° bevel :;

[Berlin]

They aren't laminated but all my vintage French mortice chisels are ground at 40ish degrees too.

[NZStu]

Well I'm not grinding it again!!:-