Sunday, January 27, 2008

The Through Tenon

The through tenon is probably the most important joint in the Arts and Crafts Style. One of the hallmarks of the style is that structural elements are used as decoration since the use of non-essential applied element are not used. Hence the use of of joinery elements to add a detail of interest to the piece of furniture. The through tenon can be cut flush with the surface and wedged, it can be left long and tusked, or in this example, camfered. The mortise is extended completely through the piece and the tenon is extended to protrude and then camfered to soften the edges. You will find this joint on everything from Morris Chairs to small cabinets, the example I'm working with here is from a Stickley small tabouret #603.

I am learning to use Google Sketch-Up, its a free 3-D design and drafting tool you can find here,, so I thought I'd give drawing up this joint.
The first thing I did was to draw the leg, 20" tall, 1 1/2"x1 1/2" square. I added the Mortise 4" from the bottom, 1/2"x2".
I made the stretcher 16 1/2" long, 2 1/2"x1", with tenons 1 3/4"x1/2", this done I added an 1/8" chamfer around the end of the tenon.

I combined the two pieces and put a peg through to hold the tenon in place. Now, this seems pretty easy and straight forward, but I have to admit that it took me longer to draw this out in Sketch-Up than it did to make the real through mortise. I spent many hours watching videos on the design, click, build blog at fine woodworking, and reading the posts there, I also spent a lot time at the Google Sketch-Up site.
Today it was time to make some sawdust and really make a trough tenon and mortise, I broke out my plan for the Stickley small tabouret and gathered some 8/4 quartersawn white oak and some 5/4 quartersawn white oak, luckily I had some cut-offs from previous projects so I didn't get into my inventory. As many of you know I build almost everything in quartersawn white oak so I keep a couple of hundred boardfeet of the stuff around.
The first thing I did was to plane the 8/4 stock down to 1 1/2", next I ripped 1 1/2" legs and cut them to 20". After marking the location of the mortises on the best faces of the legs I used my wheel marking gauge to mark the sides of the mortises and also to score a line into the face to help minimize tear out. You could also use a marking gauge or just a square and a knife.

Whatever method you use, the goal is to define the edges of the mortise on the outside face so you can start the cut from here instead of from the inside face like you would in a ordinary mortise.

There are many methods and techniques used to cut mortises, I'm not going to go into each one, just tell you the method that I have learned to be the most efficient for me. I use a hollow chisel mortiser to cut the mortises first, then I will fit the tenons to the mortises. I line up the marked location with the chisel in my mortiser and run a test cut in some of the cut-off from the leg stock. Once I'm happy with the set-up I can quickly and easily knock out the mortises on all four legs.

You can see in this picture that the chisel travelled all the way through the leg, I use a sacrificial scrap under the leg to protect it from blow-out. This leaves you with a pretty good mortise, but you still need to take it to the bench and smooth it out with a sharp chisel, this shouldn't take much more than a little paring and smoothing.

I took a few minutes to mark out the tenon on a cross stretcher so that I could set up the table saw. I raised the blade to pass through the line of the tenon and used the miter gauge's stop so that the blade would pass right at the shoulder line. I cut the shoulders on all four sides of all four legs.

Next I used the cheek cut to adjust the blade so that the blade passes just inside the cut without hitting the shoulder. I adjust the tenon jig by eye, close to, but not on the line. I know that this cut will be fat, but close, after cutting both sides I test it in the mortise. By eye I decide how much over the tenon is and adjusted the jig accordingly. I find that I can get dead on using this method in just a few cuts. This way is much more accurate and less likely to leave you with a skinny tenon than trying to measure it and setting the jig right off.

With the correct width set I cut all of the tenons and take them to the bandsaw to make the edge cheek cut, I set the fence at the correct distance and run all the stretchers through.

I like to leave my tenons a hair wide then take a couple of swipes off each side of the face cheeks with a shoulder plane this lets me get a fit that's snug, but not so tight that you have to force the tenon through the mortise.

Once the tenon is in place I like to check the extra length and mark it at the face of the leg so that the chamfer doesn't protrude into the leg.

I like to remove the material on the disk sander with the table tilted down to 45 degrees. You could use a block plane but be careful as this tends to have a little blowout since you are planing end grain.

The complete through mortise and tenon with chamfer, this is just a dry fit of course. When the cuts are finished for the table and everything is sanded I'll spread glue on the inside half of the tenon and on the shoulders and knock them in place. Once the glue is dry I'll drill a 3/8" hole through the center, careful not to blow out the other side of the leg and hammer a walnut dowel through with a little glue inside the hole. I'll cut the dowels flush and sand them smooth. The dowel adds another decorative element to the joint and helps to hold the joint tight if you have any shrinkage in the stretcher. I will complete the table in future posts and have more posts that focus on the joinery that is used in Arts and Crafts furniture.


Anonymous said...

Hello Brad,
Thanks for your tutorial and website. I have recently gotten into the woodworking world and have always enjoyed the look of Arts and Crafts furniture, so that has been my focus. I am making an end table that has thru tenons on the legs. I purchased a Powermatic Benchtop Hollow Chisel Mortiser to make my life a little easier. However, when I used it for the first time this weekend I was a little disappointed in the quality of the mortises. It cut through the QSWO without any problem, but the hole was not a perfect square. The auger seemed to extend beyond the sides of the chisel (somehow) so I had square corners with humped sides. I am using a set of Delta Mortise Chisels and thought maybe these are not the best quality or is my mortiser set-up wrong? Thanks again for everything JC

Brad Ferguson said...

I've noticed too that the Delta chisel set isn't the highest quality, you might want to upgrade if you can. I had that same problem on my old Delta mortiser, but after I upgraded to a more powerful Powermatic with better chisels its not an issue anymore. If I'm cutting thru mortises I sometimes strike the outer edge with a marking guage or a nice to get a clean line. Goodluck. Brad