sharpening a mortice chisel

[sean_in_limerick]

Hi guys,
I tried to grind the bevel on a mortice chisel last night on the Tormek 1200 - there was a pronounced curve in the bevel caused by this - i suppose that the extra length of the bevel exagerates the effect that is present on all grindings with a wheel - but i wonder what effect this has on the sharpening process. The angle of the bevel was also very difficult to setup using the tormek angle setting jig. - does anybody have experience with this? How do people normally grind the bevel of mortice chisels, do they treat them any different than - say bench or paring chisels?

Cheers,
Sean

 

[Adam]

I've never sharpened a mortice chisel on a Tormek (just about the only thing that doesn't get stuck on it), as I thought they weren't supposed to have a hollow grind. In fact the opposite - don't know who told me (ALF?) that they really ought to have a convex grind?

Adam

 

[Alf]

Yep, a little convexity is a Good Thing in a mortise chisel it seems. Somewhere I read claims that it helps "pop the chips free", which perhaps it does. Concave becomes an issue when you're prying away with a mortise chisel as regards strength, so not a good idea, while convex gives you plenty of strength. In short, forget the Tormek for this one.

Cheers, Alf

 

[sean_in_limerick]

i see -
so what are the options for grinding a mortice chisel - i use waterstones for all sharpening/honing - how do you grind your mortice chisels?

 

[j]

As a general point on grinding chisels/ plane blades.

Is it normal for none mortice chisels to have this concave grind?

If so, how do you calculate the angle for the grind?

 

[Alf]

how do you grind your mortice chisels?

Belt sander 8-[ Another one of those tools hooked up to the treadle, natch...

Cheers, Alf

 

[George_N]

The concavity is equal to the curve of the grinding wheel circumrerence. Set up the bevel angle you want eg 25 degrees and ignore the concave bit. A hollow grind (concave) makes it easier and quicker to hone a secondary bevel as the edge is thinner.

cheers

George

 

[Adam]

ignore the concave bit.

Thats the problem though isn't it? Its harder to ignore on a mortice chisel given the thickness of it. On a normal chisel, its a few millimeters thick so the hollow isn't pronounced - on a mortice chisel - its extremely thick, so the hollow becomes significant.

Adam

 

[sean_in_limerick]

precisely Adam, my mortice chisel looks bloody odd - with a big fat concave belly cut out of it - i may use a honing guide and some sandpaper to grind the bevel to 30 degrees - it's just slow - are there any other options?

 

[Adam]

precisely Adam, my mortice chisel looks bloody odd - with a big fat concave belly cut out of it - i may use a honing guide and some sandpaper to grind the bevel to 30 degrees - it's just slow - are there any other options?

A £10 grinder like this from toolstation (OK, its £12) but nontheless, a cheap way out of a fix

 

[George_N]

Could you rig up some way of using the flat side of the Tormek wheel rather than the circumference? I know some whetstones work like this.

cheers

George

 

[George_N]

precisely Adam, my mortice chisel looks bloody odd - with a big fat concave belly cut out of it - i may use a honing guide and some sandpaper to grind the bevel to 30 degrees - it's just slow - are there any other options?

A £10 grinder like this from toolstation (OK, its £12) but nontheless, a cheap way out of a fix

The wheel on a cheap bench grinder are much smaller than those on the Tormek and will therefore give a deeper hollow...or have I misunderstood what you meant?

cheers

George

 

[Anonymous]

Hi Sean,

As George_N says, the side of the Tormek wheel could be used if a small jig was made up. Depending on the width of the chisel, you could even freehand it.
I've seen Geoff Brown demo the Tormek to flatten the back on a chisel using the side of the wheel.

cheers,
Andy

 

[sean_in_limerick]

i will try to make up a jig, it sound like a good idea, i wouldn't even attempt to sharpen a garden shovel freehand!

 

[MikeW]

The concavity is equal to the curve of the grinding wheel circumrerence. Set up the bevel angle you want eg 25 degrees and ignore the concave bit. A hollow grind (concave) makes it easier and quicker to hone a secondary bevel as the edge is thinner.

As George, I use the Tormek.

Hollow grinding isn't something you do every day--at least I don't. I only grind to restablish bevels or get past damage on an edge tool. Otherwise, just honing while using keeps them in pretty good condition.

When I hollow grind, I grind at an angle a little steeper than that which I am going to hone. This actually makes the edge slightly less shallow of an angle.

I have never had levering or edge retention problems--and I use Sorby mortise chisels :lol:

Take care, Mike

 

[Nick W]

Don't I remember reading somewhere that it can be dangerous to use the side of a Tormek stone, or is that a false memory?

Safety aside, how would you restore the side to flatness after a bit of use?

 

[Vormulac]

I, too, remember reading somewhere that using the side of a grinding wheel can lead to them exploding. :!:
I'm guessing that would be high speed, heavy use and lots of pressure, as opposed to the relatively gentle application of plane blade to Tormek as witnessed at Ally Pally.

V.

 

[Nick W]

You're right about the speed thing on a Tormek. However I wouldn't describe using it as gentle, to get a decent rate of grind you need to press hard! :shock:

B.t.w I've seen pictures demonstrating how to use the angle setting jig, showing the point of contact some way up the blade. This will give an erroneous setting. The point of contact needs to be as near to where the blade meets the wheel as possible. Try setting the angle like that and then sliding the jig up the blade to see what I mean.

 

[sean_in_limerick]

whilst on the subject of the Torkek - are there methods that will reduce judder - which can be pretty bad on my setup?

 

[MikeW]

...
B.t.w I've seen pictures demonstrating how to use the angle setting jig, showing the point of contact some way up the blade. This will give an erroneous setting. The point of contact needs to be as near to where the blade meets the wheel as possible. Try setting the angle like that and then sliding the jig up the blade to see what I mean.

Yes,

Like this one from Sharp Tools USA, one of the better distributors in the US.

I would add that one also needs to check the diameter of the stone occassionaly and set the angle jig accordingly.

Take care, Mike