I’m one of those folks who thinks that it’s a pretty good idea to know how to chop your mortises by hand. Don’t get me wrong, I’m not opposed to mortising machines. Whether they’re powered by electricity or a crank, mortisers (mortising machines) can save a lot of time and energy. And, if your hand tool skills are still somewhat wanting, a mortising machine can add to precision of your work. But there will be times when it is absolutely necessary to make a mortise by hand. When that situation presents itself, you have two options. The first option is to bore out the majority of the mortise volume then clean up the sides and ends with bench chisels. The second, and for me the preferred option, is to “chop” the mortise with a mortising chisel. I choose this option because I believe it is not only faster but that it creates a mortise with more integrity than the boring and trimming method. But once again I have to say that there is not a “right” method. There’s the method that you’re most comfortable with and gives you the result that you’re looking for.
Whether you’re using an English (“pig-sticker”) or “German” type mortising chisel, you’ll notice that they’re designed for heavy work and meant to be struck with a mallet. Also, you’ll notice that they’re very “thick” in section. This strong section allows them to be used in a “prying” manner as well.
L-R; gooseneck, English (pigsticker), Japanese 1" bench chisel (for comparison), German
Chopping mortises is like every other hand tool skill – it must be practiced. Don’t expect your first hand cut mortise to be perfect.
Most texts call for starting the mortise at the ends and working toward the middle. I find that working from the middle toward the ends works much better for me. It seems much faster and I feel that I can control depth more precisely. The illustration below shows the chopping “strategy” I normally use.
Maintaining alignment that is square to the workpiece is critical. A common mistake is to “chop” from a position that is “alongside” the workpiece. This will almost surely lead to a severe misalignment problem.
Standing in line with the workpiece makes maintaining squareness much simpler.
(Note that both my friend Dave and I are committed to getting back into shape)
After you’ve got the mortise chopped to depth, clean up the bottom by using paring cuts from the mortise chisel itself or the gooseneck (also known as the swanneck or lock mortise chisel).
When fitting the tenon, remember that it’s much easier to build the tenon up (should you make a trimming error) than it is to narrow a mortise.