The Haunched and Drawbored M/T Joint - Part I
Bob Smalser, Seabeck, WA
>Part I - The Mortise
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 [i]they[/i] 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 [i]you[/i]�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.
Continued�.
