Deep(ish) Mortices For First Timer

[Karl Jones]

Thanks all. I've discovered some unloved chisels in the darker recesses of my tool cupboard that I'm going to practice getting what will hopefully be a decent edge and then have a go at some scrap before I try the real thing.

 

[RobNichols]

That sounds very sensible

 

[Karl Jones]

So after a few hours sharpening (honing) and chopping with a 12mm bevel chisel I managed a reasonably decent mortice. So my next question is - given that the mortice should be 15mm or so, do I get a chisel that wide or chop from both sides. I used a version of the Paul Sellers mortice guide (made from some aluminium plate I had hanging around) so could just use that on either side of the mortice and just use the 12mm chisel I have, or I could just get a 14mm or 16mm chisel.

What would you suggest?

 

[Jacob]

So after a few hours sharpening (honing)

Should have been a little and often and taking up about a minute or two in total, several times during the chopping of a mortice.
It's when you are working hard with a chisel that modern sharpening fiddling about is just too time consuming. Back to basics - freehand, one medium oil stone.

and chopping with a 12mm bevel chisel

Wrong chisel

I managed a reasonably decent mortice. So my next question is - given that the mortice should be 15mm or so, do I get a chisel that wide

Yes if it's a mortice chisel, 5/8" or 1/2", but otherwise you use whatever you have, as best you can, though a firmer would do better than a bevel edge.

or chop from both sides. I used a version of the Paul Sellers mortice guide (made from some aluminium plate I had hanging around) so could just use that on either side of the mortice and just use the 12mm chisel I have, or I could just get a 14mm or 16mm chisel.

What would you suggest?

A proper mortice chisel is a specialised tool designed for the job, with a technique all of its own. You could go there if you wanted to, otherwise just carry on as best you can with whatever is to hand.

 

[Karl Jones]

Should have been a little and often and taking up about a minute or two in total, several times during the chopping of a mortice.
It's when you are working hard with a chisel that modern sharpening fiddling about is just too time consuming. Back to basics - freehand, one medium oil stone.

Wrong chisel

Yes if it's a mortice chisel, but otherwise you use whatever you have, as best you can.

A proper mortice chisel is a specialised tool designed for the job, with a technique all of its own. You could go there if you wanted to, otherwise just carry on as best you can with whatever is to hand.

Thanks Jacob - the chisel was what I had to hand, and the sharpening was a learning curve for me, so I probably took longer than I needed to or should have done. I found 4 chisels and have them all the treatment, and chopped the mortice - that was over the couple of hours I mentioned.

At the risk of asking a stupid question, what's the difference in technique between the two chisel types?

 

[Jacob]

...

At the risk of asking a stupid question, what's the difference in technique between the two chisel types?

Not a stupid question at all! I had no idea myself until and old joiner patiently showed me how!
You cut out the whole mortice with a mortice chisel of same width, a big mallet, no other tools.
Mark up the sides with mortice gauge, top and bottom if it's through, mark ends with a square
You hold it vertical at all times, no levering at all except a little pull back to loosen it from each cut, and also to clear the bottom of a blind mortice.
You bash it in anywhere but not at the ends, these you do last.
Loosen it out of first shallow cut and then repeat by paring off the vertical face of the cut and going deeper, repeat etc.
When close to the end turn around and work your way back, cutting through the chippings you've already made and going deeper with each cut, paring down the face of the previous one.
It's a fast and furious process and good for body building!
When halfway through turn it over and work from the other side, if it's a through mortice.
Otherwise work to a depth mark, felt tip mark or sticky tape.
Finish by cleaning the faces at the ends of the mortice with a last paring cut.
Clean out the bottom of a blind mortice by levering against the side with the curve of the bevel against it, and lever out any remaining chippings. Most of them will have just fallen out as you go.
Sharpen a little and often through the process.
Do it flat on a bench top un-clamped and not in a vice - there's a lot of heavy bashing and the clamps will mark the sides.
Better still do it between your legs sitting astride the workpiece over two saw stools, or even a purpose made morticing stool.
It's much the same process as you would apply with a hand powered morticing machine, just a series of powerful vertical paring cuts, close together, down the face of the previous one.