Chopping Mortises – For Power Tool Users

[Bob Smalser]

Ken can move or delete it if he chooses, but it was put here on purpose for those newcomers looking for a mortising machine.



In a small response to years of subtle but predatory marketing on PBS that has newcomers asking about mortising machines for their early projects, I prepared a short primer this morning in the shop to answer a younger man’s question. The entire session, including stock preparation and photography, took 30 minutes. The actual mortise chopping took 4 minutes, and I wrote this up on my lunch break.

First, you need mortise, not paring chisels. These Japanese ones below I bought from Highland Hardware when they first opened more than 2 decades ago to replace the badly worn family ones.



Note the flat bevels in the photo above; not hollow ground and no secondary bevel. These are laminated blades designed for striking, and they come in the exact width of your intended mortise, ¼, 3/8, and ½ inches.



Also note that the backs are hollow ground to facilitate easy flattening as you hone them during their life. You can see the hollow above the edge.



Their bevels should be touched up on the hone every time you use them; your stones ready for use should be a permanent fixture on a corner of your bench. Honing these is easy; just index the flat bevel on the stone. You also need to hone the back dead flat, and I also hone the sides lightly on the fine stone to remove any burrs. I use a set of 4 Arkansas stones all the way to the finest “black” grade, but you can use what you normally sharpen with. I wiped the oil off the stone and chisel for clarity; don’t hone them dry or the stone’s pores will clog.



I do a final stropping on the stitched muslin wheel with Knifemaker’s Green Rouge. Hard felt wheels are the best for this, but they are expensive.



Then I lay out the mortises on the prepared stock. First, the mortise gage double tines are set to the width of this half-inch chisel. Then the mortise gage fence is set for mortise location on the stock, and lines scratched. Want to have the mortises dead center? Simple, just run the fence down the other face of the stock, compare the marks, and adjust the fence until the marks are identical.



It’s a simple matter next to mark your mortise width with try square and marking knife. I’ll cut a simple blind double mortise and have used a pencil to make the lines clear in the photograph. You need to leave your pencils in the drawer for this and other joinery marking, as they are insufficiently precise.



Index your mortise chisel plumb in the end knife cut, and strike with a wood mallet. Do all four ends.

Continued on Part II

[Bob Smalser]

The next chopping sequence is from the center of the mortise, and the waste merely levered out…splitting rather than cutting the wood along its long grain. My training aid today is a 2 X 2 of sopping wet Douglas Fir from the scrap pile out in the weather…. hard, tough and splintery. Your dry cabinet hardwoods will be easier. When working with highly figured wood such as Birdseye Maple you are afraid to split, then simply strike the outline of your mortise lightly with a paring chisel, first.



I repeat chopping from end and center, levering out the waste until I reach the desired depth; then I reverse the chisel and use it bevel-down to clean up the mortise bottom.



The final result is a little furry because of the wet wood, but entirely satisfactory. There is a small chip-out at the top of the right mortise, but this will be completely hidden by the tenon shoulder when assembled.



Frankly, even working in large, commercial, 3-phase shops, I never found many mortising machines that were entirely satisfactory. The bits are difficult to sharpen so you need two sets of them for production work, and the over arm design likes to flex under pressure, especially when the bit is getting dull, which also tends to pull your work piece out of alignment with the fence.

Why bother? These simple, inexpensive tools and a shop-made mallet are all you need to do mortise and tenon joinery on one-off projects for the whole of your lifetime.

[Jim Stastny]

Thanks!!! The more I get involved in WW the more I learn that hand tools may do the job quicker and with a lot less expense than power tools. Not only that, but they don't take up as much valuable shop space.

[Charles McKinley]

Thanks Bob!

Another keeper and I'll be investing in a set of chisels rather than a machine.

[Bob Smalser]

FYI, I posted this today on a professional forum:

As I've said, I'm no stranger to or critic of automation where it makes sense...but the WW Forums today are filled with newbies whose only exposure to any kind of teaching are from PBS's Norm-Delta Enterprises or trendy magazine and book authors...

...and much of that "teaching" is self-serving to the point of predatory.

Its a sad reflection on all of us older, more experienced guys that a 30-year-old new father asks what kind of mortising machine, pockethole jig or biscuit joiner he needs to make his first project...a cradle for the new baby.

I know he doesn't have that kind of dough to waste as I suspect things haven't changed since I was in that position...and are probably worse...and I feel there is a community responsibility we aren't meeting, here.

Chopping Mortises – Feedback after 18 hours.

Thanks so much for a clear concise explanation of a topic that seems so mysterious to many of us. I agree with you on the inherent problems with power mortise chisels and I am ashamed to say that I don't even own a set of hand mortising chisels. But thanks to your informative and enlightening article I will now purchase a set.

I appreciate the straightforward information.
Is this available on a Webpage??
I'd like to show it to others.

Thanks you, Bob. I just learned a ton of stuff. Most of my understanding of this seems to have been wrong. That's why I rely on the machine.

That was about the clearest description I have ever read about chopping mortises in my life. And, I have read LOTS of books.

Wow, great...I love when I can wake up and get new information every day!!! Thank You Bob!!!

Thanks Bob for taking the time to put this together. It will help me a great deal. I chopped a few mortises last weekend, and I did well, but this tutorial helps clear things up, not to mention saving me money on not buying what I don't need.

Oh yeah --- Thanks Bob for all the help you've given in trying to keep the art alive. I'm glad I converted before I spent too much on the machine tools. I'm far from proficient, but I'm learning (and enjoying).

Bob, your posts are informative, very interesting, and well thought out. You are a real master of all phases of woodworking. Thanks for the posts.

Thanks, Bob, for setting some time aside and putting this great lesson together. This demystifies much of what I was doing wrong when I was doing some practice M&T projects. Not only do I like your thoughtful, informative approach, but I appreciate how you started with the step-by-step tools and materials preparation stages and went on to the end.

I'm going to invest in some mortising chisels now and go back to the garage for another shot at things. Be advised that I'm going to make some copies of this post (along with the color pictures) with my printer and post them up above my bench.

It sure would be nice to have a dedicated section on the Woodnet Forums that showed more helpful step-by-step instructions like yours.

I really enjoy your tutorials. I've rehabbed chisels and chopped mortises for years, but I can always learn something from a thoughtful and experienced teacher.

Thank YOU Bob! I think you just saved me from a power tool purchase that I don't have bench space for anyways.

It is a pleasure to read your very detailed posts. I learn a lot every time I log on and read your stuff. Many of us like the details that a book wood otherwise leave out. This comes from actually doing something or trying various methods until something works. Once again thanks for your attention to detail.

Bob thanks for taking the time to post these jewels. I find myself fascinated with things I didn't think I had an interest in. They are the best kind of writing.

Thanks for the nice article with photos. You have added a new technique to chopping mortises that I haven't seen before. Something I will be practicing tomorrow as I prepare to chop mortises in a real project.

Previously, I only knew two techniques:
1. Little chops all along the length of the mortise, then clean out. This is what I was taught in high school and never mastered.
2. Chop aggressively in the center to the depth required and work towards to the respective ends of the mortise. This one I saw in an Ian Kirby article on this subject in (I think) American Woodworker. So my sum total of knowledge on this subject has increased by 50%. That makes today a good day.

You have gotten me interested in various aspects of old-time woodworking using hand tools, etc. And you're still going!
I'm thinking that your posts should be collected in one place where one could go and see all of your work.

Wow. Thanks for taking the time to give the lesson. Only thing is now I have to go get me some mortise chisels.... That's a good thing....

Thanks for the info. I have a very small shop with no room for a bunch of specialty power tools. Thus, I've learned how to hand cut dovetails and mortises. Your method of marking the mortise will significantly reduce the time it takes compared to the method I've used.

Terrific presentation, Bob. Your photographer did a great job also. Awhile back I was going to buy a new mortising machine. Then I said to myself, "Nope, I'm sticking with my hand chisels." Besides, I still on occasion like to shape rounded tenons.