The Haunched and Drawbored Mortise and Tenon

Part I: The Mortise

by Bob Smalser

This article first appeared as a thread on theWoodNet woodworking forum. It was compiled and reproduced here for easier public consumption. All Text and Images are the property of Bob Smalser.


One of the strongest joints, the haunched and drawbored mortise and tenon is one of the few that resists stresses in any direction, to include tension, and is a joint that will remain fully functional long after any glue has deteriorated to dust. A basic joint used to join structural members, I'll walk you through cutting one today by hand to join the top rail to its post for a small work table done in hard maple. Why by hand? Not because I'm some hand tool reactionary.I use machines for the jobs they do best and hand tools for the jobs they do best.but there are some joinery principles best displayed and photographed using hand tools, and as most teaching today involves machines almost exclusively, newcomers tend to miss the parts where the cheaper hand tool does the job much, much more efficiently than the expensive machine, especially on smaller hobby projects.

Plus, not enjoying any subsidies from major machine or hand tool manufacturers or retailers, I'm free to provide counsel on what's best for you.not what's best for my sponsors.

The basic joinery tools I'll use are shown above. None except the shop-made mallet are newer than 30 years old and some are almost a century old.yet I could replace all of them in a few months of shopping at flea markets and collectible tool auctions for less than 200 dollars, simply because my first training 4 decades ago as a teenager in a boatyard was in basic hand tool sharpening and maintenance. Yes, the shoulder plane is relatively expensive, but they are indispensable even for machine woodworking and sound but scuffed ones like this Stanley 93 can still be had in the 60-dollar range. 3-tined adjustable mortise gages along with the old Disston saws can be found used for less than 20 dollars, and the large mortise chisel is a recent acquisition as part of a salvage chisel lot that cost less than 5 dollars.

My point is that a newcomer's first steps shouldn't be making furniture for the house or that first fancy dinghy, they should be acquiring and tuning the necessary tools and learning to use them in traditional construction of simple benches, shelves, assembly tables, horses and jigs for your first shop. Why traditional construction? Because its study and practice with hand tools will teach you more about your material.wood.than machines will, and it never ceases to amaze me how little even some advanced craftsmen understand about their material. Hand tools allow you to feel how steel wants to move in cutting wood based on the grain of the wood and creates an understanding that applies to obtaining clean cuts using machine tools as well. It will pay off in the long run to your pocketbook, your enjoyment and your skills, as it's easier on all to make those first irreversible mistakes in 50 cents worth of maple than 80 dollars worth of mahogany.

The mortise should be cut first, and I'll chop one with the chisel. This is a long, millwright's mortise chisel made by James Swan almost a century ago. It's not a "framing" or "firmer" chisel as described by many tool dealers or collectors, it was manufactured primarily to chop mortises in window, door and millwork factories more than for tradesmen, who generally used smaller "sash" mortise chisels more easily carried in a carpenter's box or shipwright's chest. All mortise chisels come in widths to match the intended mortise, but these millwright chisels are much longer and easier to hold plumb, much heavier, and combined with the right mallet, much more powerful.

And with power comes speed and efficiency. I set the mortise gage to the exact width of the chisel.

.and use it to lay out both mortise and tenon on the squared-up stock. I darkened my lines with a pencil and drew some otherwise unneeded lines for clarity, but laying out your joints should be done with marking knife and awl, not a pencil. The knife used across the grain and the awl used with the grain is not only more precise, it provides accurate recesses to index chisel or saw, and as you will see, scribes the wood sufficiently to prevent unwanted splitting and chipping while cutting or chopping.

This is a 6/4 by 3" post and a 5/4 by 2" rail, and I'll do a by 1 " mortise a 16th of an inch over deep to house a 1 " long tenon. Mortises should always be slightly over deep to allow room for glue squeeze out. A 7/8" wide mortise would also be acceptable here. The "haunch" is the 45-degree tenon stub I've drawn on the upper face profiles of the stock that increases the gluing surface and aids in the joint resisting twisting stress.

You can also see in the photo above that if the rail is to be flush with the post top, then I've crosscut the post too long. You are correct, I have. The post's short grain on the topside of the mortise will be far too fragile to chop a mortise and haunch without predrilling.and predrilling is unnecessarily slow, so I'll chop my mortises vigorously and trim the tops of the posts later.

The first two chops are plumb to the work piece and just a bit inboard of the mortise ends. Inboard because that lead-weighted hard maple mallet weighs over 2 pounds, the bevel on this striking chisel is a steep 35 degrees, and hard blows downward tend to push the chisel backwards just a tad. Although it is the cheeks of the mortise that provide the majority of gluing strength, avoiding unnecessary stress or damage at the ends is simply better craftsmanship.

I've also marked my required mortise depth on the chisel using masking tape.

The third blow is taken bevel up about a third of the way along the mortise's length at an angle downward toward the end.

.and the waste levered out, splitting along the grain of the wood. The deep scribe marks from the mortise gage prevent any chip out.

The fourth blow is identical from the opposite direction and that waste levered out. Subsequent blows continue with two plumb blows at each end followed by two angled blows and levering out waste.

.as the mortise gets deeper, the obstruction of the mortise ends force the angled blows increasingly steeper, eventually preventing them from reaching within clean splitting distance from the end blows.the chisel is then flipped and the angled blows struck bevel down to keep the cutting angle sufficiently acute for clean, 4-chop split outs.

Upon reaching the correct depth, the mortise bottom is squared and cleaned by lightly striking the chisel with the bevel instead of the blade back indexed against the mortise end .

.and the top of the chisel bevel used as a fulcrum to scrape the mortise bottom with the edge of the tool. The added leverage of the longer length and larger bevels of these heavier mortise chisels also make this an incredibly clean and efficient technique to get out that last 16th of depth, if you find yourself a tad short.

The haunch is chopped by lightly striking its outline.

.then using a bevel gage or sight line to line up one, clean 45-degree chop. These can also be cut square and a corresponding notch made in the post. Unlike the square ones, the angled one I'm using today is completely hidden.and technically should be called a "miter haunched drawbore mortise and tenon".but that's a bit of a mouthful for a subject line.

The end result is a clean, accurate mortise done in mere minutes. Depending on the size of the mortise.in average-sized furniture stock and using the right tools, they can be chopped at the rate of between 6 and 20 per hour with very little practice at it..on many pieces faster than the time needed to set up and test a router jig.

 

Q&A - Mortise

Quote #1:

"If the workpiece is held solely by friction in the jaws, this places a lot of stress on the vise and its fixing to the bench. Even if a spacer is placed below the workpiece so it site directly on the guides and/or screw, it's needless. Much better morticing work holding is had by placing the workpiece on the bench top. If your bench is truly massive, anywhere will do. If your bench is a little lighter, over a leg is the best.

To hold the workpiece, you can either clamp a piece of scrap DOWN on the workbench, and then clamp the workpiece horizontally to the scrap. Proper 'G' (AKA 'C') clamps are best for this, since the shock of chopping tends to make 'F' clamps lose their grip.

Alternatively clamp a hand screw to the workbench, and hold the workpiece in that, In either case, a wonderfully solid support is obtained. If you really do a lot of morticing, you might consider a dedicated morticing stool/bench."

Quote #2:

"Very interesting. I'll have to try chopping in the vise, which I have avoided due to early teaching. I have a Record made into end vise with 4th pair of wooden (this time beach) jaws just installed and I hope I can apply enough pressure.

I have tried holding the piece to be chopped with a holdall but it tends to slide along the bench top and that leads to all kinds of contraptions. I have a continuing problem with the chips if the mortice is short and narrow, especially as I get deeper. So far the best solution has been to use a narrower chisel to pry them out but it's not very efficient. I'd be interested to know your solution. "

Great input and thanks. But just put a spacer block in the vise so the force is directed to the rails instead of the jaws of your vise and you won't hurt anything. Most of the folks I target don't own a good bench yet.nor do boatbuilders working out of a tent. I always figured the old adage about not banging on the vise dated from the days of wooden threads and rails.

The chips do get smaller as the hole deepens, but if the mortise is cut clean, the chisel used bevel down can be used to flip them out using both hands. I didn't have to remove the work piece from the vise to empty chips once in the sequence shown.

Again....don't worry about the vise....an old patternmaker I used to know, who used a his big Emmert for everything including tasks I have a 20-ton press for, would chuckle at concerns about using a wood mallet on one.

Quote #3:

"I love Arts and Craft style furniture so I have a lot of mortise and tenon cutting in my future. I don't doubt your expertise but being new to this I learn from reading and then trying to do what I've read. When I read things that appear to contradict each other then I question why and which source is right.

I read that the tenon should be at least 1/2 the area of the end grain on the rail and should extend 2/3 of the way into the post. If my math is correct (never was my best subject) then your tenon should be 1 & 1/2 by 5/8 not the sizes you listed.

Is there a reason why your is different? Was what I read wrong? Has experience taught you otherwise? "

Nothing wrong with your rule of thumb.it's just not near as critical as some make it out to be, IMO. The joint is so incredibly strong that a little bit here or there isn't important...especially in larger scantling sizes. That rail would break in the center long before either your or my joint failed....and take too much out of the post and it'll simply break there, instead, if it's dropped off of the loft.

A one-inch wide mortise would be comparably fragile in the mortise cheeks for those drawbore pins, though.... and 7/8 would be the widest I'd go.

Two reasons for the size I chose:

  1. It's a short assembly table.... I want some meat left on the outside of the posts to later dado in a shelf if I need one.
  2. My 7/8" mortise chisel isn't as photogenic as that lovely 3/4" Swan.

    Quote #4:

"You _do_ know don't you that somebody out there reading this is thinking "gee, I can cut tenons with a Unisaw equipped with a tenon jig and I can make mortises with a dedicated hollow chisel mortiser so why is this Smalser guy wasting our time with this hand tool stuff?" (wink) "

Of course I do....as I inferred, I cut tenons primarily on the TS, too.and 25 years ago I cut thousands of mortises on big, honking 3-phase Powermatic overarm mortisers long before benchtop homeowner models came out.

Those mortisers were finicky, expensive pains in the butt, given enough use. Get two or three sets of the best bits you can buy, consider fabricating a stronger hold-down, and find a good sharpening service, as too much pressure on that lever will permanently ruin their alignment, making them even more finicky.

Why bother if you are a hobbyist making heirloom one-offs or boats with a limited tool and wood budget? On one-offs at a commercial pace, my standard for hand-chopping versus the router and jig or booking time on the over-used mortisers used to be 12 mortises using expensive laminated Japanese mortise chisels. Now that I've scrounged these better millwright chisels, that standard has increased to 16 mortises and the Japanese chisels were sold.

Quote #5:

"Have you posted an article on making the lead weighted mallet? "

No.just turn yourself a mallet, copying whatever one from a catalog or website you like......bore deeply into the end using your largest Forstner bit.......pour molten lead or wheel weights in there and let it cool...do it outdoors wearing a respirator....hammer the shrunken lead tight using a punch......and fabricate a bung on the lathe to cover the hole with a contrasting wood.

This one is merely a hunk of Bigleaf Maple chainsawed from a large crotch with a Purpleheart bung.

 

Next: Part II - The Tenon

 


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