Adjust Narex Mortise Chisel Bevel Angle using Bench Grinder

[Curt Putnam]

I have a 1/2" Narex mortise chisel which has a primary nevel engle of 35° which I would like to reduce to 20°. I have a brand new grinder with CBN wheel. I am a total newb at using a bench grinder like this. It is equipped with the Tormek tool rest but there are no jigs to fit such a thick chisel (that will hold it square.) After ruining a couple of old and not valuable chisels I am beginning to get the hang of things (note the emphasis on beginning.) Neurological issues require that I use a jig to maintain square and projection.

My questions are:

Where on the existing bevel or shank should I start grinding?
How do I know how deep to go?
What jigs are available to help with the task?
Given the length of the bevel at 20°, can it even be done on a bench grinder?

I will very much appreciate any help and thank you in advance

[justin sherriff]

Why do you want to go to 20° on a mortise chisel?
should be fine with a bench grinder.
I would start back up on the bevel so as not to over heat the edge.
nice jig https://www.leevalley.com/en-us/shop...t?item=05D1302 Should not need it for what you are doing.
How do you sharpen after the grinder?

[justin sherriff]

All so do not let the chisel get to hot. If you can not touch it you are getting hotter than I like to go. To hot and you can lose the temper.

[David Eisenhauer]

Some of the "pig sticker" type mortise chisels have a long 20* primary bevel with a shorter, steeper 35* bevel at the actual cutting tip. Just hold it as square as you can Curt, check often with a square and adjust your technique as required. You will develop some muscle memory as you do more of it and probably be holding it pretty square in a short while. The chisel will last through many, many grinding/sharpening cycles and should not suffer any permanent damage due to initial, not-as-skilled grinding sessions.

[Derek Cohen]

I have a 1/2" Narex mortise chisel which has a primary nevel engle of 35° which I would like to reduce to 20°. I have a brand new grinder with CBN wheel. I am a total newb at using a bench grinder like this. It is equipped with the Tormek tool rest but there are no jigs to fit such a thick chisel (that will hold it square.) After ruining a couple of old and not valuable chisels I am beginning to get the hang of things (note the emphasis on beginning.) Neurological issues require that I use a jig to maintain square and projection.

My questions are:

Where on the existing bevel or shank should I start grinding?
How do I know how deep to go?
What jigs are available to help with the task?
Given the length of the bevel at 20°, can it even be done on a bench grinder?

I will very much appreciate any help and thank you in advance

Curt, while you can freehand grind a thick blade on the Tormek BGM-100 using the flat blade rest from Tormek ....



.... I do not advise a hollow grind for this chisel. If the Narex comes with a 35 degree bevel, and if you really wish to reduce it, I would use a belt sander ....

This is a grinding rig I designed and built and was published by FWW magazine in 2005 ...



Two versions:

http://www.inthewoodshop.com/Woodwor...rinderMkI.html

http://www.inthewoodshop.com/Woodwor...erMK%20II.html

Now the other matter is what angle is better? For years I have had 20 degrees for the primary and a 35 degree secondary. I am now trying out a 30 degree single face with a Unicorn profile for extra strength (Japanese mortice chisels). The question is whether a mortice chisel is all about penetration, or whether it is penetration and leverage.

Regards from Perth

Derek

[Oskar Sedell]

draw a 20 degree line (or mark with tape), representing the new bevel. Remove all metal on the wrong side of the line.

[justin sherriff]

I do the same thing on a belt grinder but I just use a cheap knock off eclipse honing guide. I put it rite on the belt and the roller wheel spins with the belt so there is no damage to the guide cheap and easy.

[Warren Mickley]

I would hold off changing the bevel until you have some experience making mortises. Once you change the bevel it is a lot of work changing it back to a flat bevel. It is considerably more work going back than altering it in the first place.

In both the Japanese and European traditions we ride the bevel in mortising. A single flat bevel is the most efficient configuration, and has been for centuries.

[Alan Schwabacher]

I don't have the experience of many here, but have noticed that a mortise chisel makes mortising more straightforward, even though a bevel edged chisel can penetrate the wood more easily. I think the difference is the size of the bevel that pushes wood aside as the chisel enters. I think that's useful, and would be diminished with a shallow primary bevel, beyond any difference in prying.

I'm interested to hear whether any of the more experienced here think this makes sense.

[Charles Guest]

Hone on the 35* bevel you have and see if you can actually cut an accurate mortise. A good test is a frame (think cabinet door) that goes together flat and square, and can be picked up by a stile and held horizontally and the good friction fit of the mortise and tenons supports the entire structure without it coming apart or frankly without any slippage whatsoever. There is nothing about a 35* mortise chisel that would hinder this effort in any way. If a joint or joints are so lose that parts start to slip if not outright fall to the floor than that's unacceptable. Changing the bevel angle on the tool wouldn't help fundamental errors in laying out and/or executing the four joints in the frame.

Once you can reliably do this, then you're ready to tweak the tools to your exact preference though you just might find you like it fine as is.

[Andrew Pitonyak]

Am I the only one who wants to know why the lower angle? I am curious...

I like the jig Derek.

Had not occurred to me that I should not hollow grind a mortise chisel, never gave it a thought. Glad I did not do it.

[Curt Putnam]

Thank you all!

I have decided to stay with a flat bevel at 35° for the moment. The impetus for wanting to change the bevel angle is the issue of penetration. Punching a 35° into wood takes some serious whaling on the chisel. Doing so accurately slows me down. My Sorby has a 30° primary and a 35° secondary and seems to sink deeper with more ease. Just like a politician, I reserve the right to change my mind and think of some other silly thing.

[Charles Guest]

Thank you all!

I have decided to stay with a flat bevel at 35° for the moment. The impetus for wanting to change the bevel angle is the issue of penetration. Punching a 35° into wood takes some serious whaling on the chisel. Doing so accurately slows me down. My Sorby has a 30° primary and a 35° secondary and seems to sink deeper with more ease. Just like a politician, I reserve the right to change my mind and think of some other silly thing.

If the Sorby works better for you, then use it. Why make things harder for yourself? You can also just use a regular bench firmer chisel - beveled or straight. The point being is that you have tools in your shop right now that will cut perfectly functional mortises. There is unfortunately no chisel, or chisel set up, that will guarantee perfect results every time. The only thing that will do that is a very high quality dedicated mortising machine. The most exquisitely made and tuned mortise chisel in the world will happily chop one 10* off vertical if that's the direction you're pointing it in.

Otherwise, try cutting a center V all the way to depth (see the Kirby article as he articulates this method about as well as anybody). After you've done this, the chops to the mortise ends should go from top to bottom with one or two strokes. You can also drill a hole to depth around the center of the mortise and work your way back. It's helpful to give the waste somewhere to go. Your goal is a pretty darned accurate mortise the majority of the time. Everybody chops one a few degrees or so off occasionally (see the 2nd video) and there's a fix for that that doesn't involve remaking the part or having an overly loose joint. Minor adjustments do not a failed joint make.

https://www.woodworkersjournal.com/hand-cutting-mortise-and-tenons/

https://www.youtube.com/watch?v=XhtD14Qn5pM

[Warren Mickley]

. It's helpful to give the waste somewhere to go

Yes.

"Penetration" is only important if you do not give the waste somewhere to go. The mortise chisel acts as a wedge to drive new material into the old cavity. A flat bevel makes the best wedge.

[Charles Guest]

Yes.

"Penetration" is only important if you do not give the waste somewhere to go. The mortise chisel acts as a wedge to drive new material into the old cavity. A flat bevel makes the best wedge.

Yes, you have to pry into a void. Otherwise, it quickly becomes a muddle of half crushed half cut material and things just go downhill from there. Remembering the cardinal rule, a mortise could be cut with a sharpened flathead screwdriver if somebody was holding a gun to your head.