Chopping Mortises – A Quick Tutorial

[Bob Smalser]

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.

http://pic3.picturetrail.com/VOL12/1104763/3442941/42267813.jpg

Note the flat bevels; 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.

http://pic3.picturetrail.com/VOL12/1104763/3442941/42267803.jpg

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

http://pic3.picturetrail.com/VOL12/1104763/3442941/42267831.jpg

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.

http://pic3.picturetrail.com/VOL12/1104763/3442941/42267823.jpg

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.

http://pic3.picturetrail.com/VOL12/1104763/3442941/42268050.jpg

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.

http://pic3.picturetrail.com/VOL12/1104763/3442941/42268027.jpg

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.

http://pic3.picturetrail.com/VOL12/1104763/3442941/42268019.jpg

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]

http://pic3.picturetrail.com/VOL12/1104763/3442941/42268006.jpg

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 figures wood such as Birdseye Maple you are afraid to split, then simply strike the outline of your mortise lightly with a paring chisel, first.

http://pic3.picturetrail.com/VOL12/1104763/3442941/42268181.jpg

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.

http://pic3.picturetrail.com/VOL12/1104763/3442941/42268168.jpg

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

http://pic3.picturetrail.com/VOL12/1104763/3442941/42267794.jpg

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.

[Lloyd Robins]

Thank you very much! I am glad that I looked at this posting. :)

[Randy Gleckler]

Bob,

You are a wealth of information.. Thanks for sharing.

Randy

[Gene Collison]

Bob,

Thanks for the great presentation. Well done and appreciated!

Gene

[John Wadsworth]

Bob,

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.

Keep 'em coming...

John

[Tom Scott]

Thanks for the new tutorial. All of your good instructions really need to be made into some articles that can be referenced later on when someone asks the same question.

My process is slightly different in that after I register the first cut on each end, I will start at one end (as opposed to the middle) and go all the way across. After you clear the first few chips, your chisel goes progressively deeper with each cut, so that by the time you're at the end of the first pass you are almost full depth (depending on how hard the wood is). Then you reverse and go the other way. I will give your method a try, though, as it may be even a little faster.

Tom

[Ace Karner]

Why isn't this posted under articles?

[Wendell Wilkerson]

Why isn't this posted under articles?

All of Bob's tutorials should be put into the articles section.


Wendell

[Terry McClean]

Great post. It goes well with your other posts, chopping mortises, and your display of home made tools.

Any chance of a similar posting where plane and saw are used to dimension lumber instead of tables saws, jointers, and thickness planers (are there other kinds of planers?)?

[Terry McClean]

Forgot to mention the plane rehabilitation post. Also very interesting and informative.

[Bob Smalser]

"Any chance of a similar posting where plane and saw are used to dimension lumber instead of tables saws, jointers, and thickness planers (are there other kinds of planers?)?"

Well thanks, but these are no big deal...I merely carry the camera in my shirt pocket to work. "Milling Earl's Fir" is the one most instructive to most home woodworkers, IMO, as it details the board's relationship to the tree, which is helpful to understand why wood moves and warps....much of your problems the sawmill's fault, not yours.

No shortage of experienced, traditional joiners here....but not many experienced sawyers.

I've been asked to do one on scraping, first.

But I will one day - my favorite class for schoolkids when my boys were young was to bring in the tools, scrap cedar and clamps, set up a half dozen cafeteria tables, do a demo with froe and planes on making a board from a tree limb, then demonstrating how all the various hand tools worked...

...and letting the kids have at them themselves.

Braces and bits were the clear favorite, followed by planes and spokeshaves.

Never had a kid cut, and the teachers had as much fun as the kids. And I'd bring in a box of cedar offcuts nicely planed and rounded for kids to take home for their woolen drawers.

But generally, I use a power jointer and thickness planer like most...just like I use a 26' Lucas portable mill rather than a pit saw. The hand tools come into their own in fitting, detailing and finish work...much of the misguidance bandied about these days being that the machines need to be precise enuf to eliminate the hand work...which is a waste of time and money, IMO.

When folks want to know why these...

http://pic3.picturetrail.com/VOL12/1104763/2594266/31846085.jpg

Look so much better than these...

http://www.tools-for-woodworking.com/images/products/handsaws/051101.jpg

...its simply a function of changing radius curves in three dimensions that only can be done either by hand or on a spindle sander with air-inflated sanding drums, which are rare accessories not in many shops...and are much more difficult to grind fair curves with than hand tools.

[Angelo Schembari]

Just went and chopped out a mortice or two with a chisel I just rehabbed. Nice little chunks of cherry just poppin out.

<img src="http://img.villagephotos.com/p/2003-8/352123/morticedone.jpg"><p> Nice to know that this was done with tools that were made before I was born. In the case of the chisel, at least 100 years before I was born! Thanks again Bob. In the future I will use the chisel rather then set up the router for mortices...seems faster and much more rewarding.