Jointry question for a bed

[Tom Hoffman]

I'm building a footboard for a bed. I'm planning to do a large mortise and tenon joint. If you look at the picture you'll see that it essentially is the same as a breadboard end on a table. But, I'm worried about wood movement. The wood is 6/4 poplar. If I do this would two dowels near the center glued, then dowels on each end with elongated holes be OK?

Or, is there a better way to skin the cat?

Ideas appreciated.

[Jamie Buxton]

Tom, I can't see that pic. All I see is a block with a red X in it.

[Tom Hoffman]

I thought I could post a .doc (Word document). I converted it to .jpg. Lets see if this works.

[Mike Cutler]

Tom. I'm about to complicate your life and your joint.

If I'm guessing right, you are about to mortise ~28". This is going to be problematic. You run the risk of significantly weakening the upright piece.
The mortise should be broken up into smaller widths and haunched at the ends. I would do three mortises 1 1/4-1 1/2" deep by 4" long, by 3/8" thick, with haunches on the ends of the outer tenons. Center one mortise and place the others at a distance to the centerline of the tenon 2/3 of the distance to the end. Cut a shallow recess that will run the entire length the thickness of the headboard for a nice clean joint line. Glue the center Tenon completely, and pin it in one place, and drawbore the outer tenons. This is where you will "elongate" the draw bore hole in the tenon(s).
My .02 fwiw

[Mike Wenzloff]

Hi Tom, I second Mike's recomendation, with the following. The tenons should also be bridged by a haunch between the larger tenons so gaps do not show along the joint.

That may be what Mike is recommending, but I'm tired and wanted to make that clear.

Thanks, Mike

[Jamie Buxton]

The mortise should be broken up into smaller widths and haunched at the ends. I would do three mortises 1 1/4-1 1/2" deep by 4" long, by 3/8" thick, with haunches on the ends of the outer tenons.

If he cuts one mortise which is 28" long by 1 1/4" deep by 3/8" wide into a post which is 2 1/2" square, there's still going to be lots of wood left in the post.

[Mike Cutler]

Jamie. No doubts that there would still be a lot of material left in the post. In the vertical plane the stress would be minimal and the mechanical properties would be strong as all get out. I was mainly considered about the side load stresses applied to the entire face of the joint. A 28" tenon on the end of a headboard would be a pretty powerful lever.

Mike that is what I meant to do. Haunch the space between the tenons. It was late for me also, and I had just gotten finished snapping the handle off of my Delta Mortiser, doing pretty much what Tom is doing in his project. My project is a door though.

[Tom Hoffman]

Guys: Thanks for taking the time to help me; it is very much appreciated.

Mike: I need some clarification: When you said, "Cut a shallow recess that will run the entire length the thickness of the headboard for a nice clean joint line," I'm not sure I understand. Do you mean create a shoulder on the tenon?

Also, what does "drawbore" mean?

Should the dowels go all the way through the bed post?

Thanks, Tom

[Mike Cutler]

Tom. Yes. I meant to put a shoulder on the tenon the whole length. It wouldn't have to be very deep, maybe 3/8".
"Drawboring" is the technique of drilling the holes in the tenon stock about 1/32"( max)off of the holes in the post. It causes the joint to pull it self in tight, in otherwords, the hole in the tenon stock would be 1/32"(max) closer to the shoulder The joint will still have the ability to expand and contract.
In the case of you head
board I wouldn't expect a whole lot of expansion and contraction. Unless the room it is in will have wide humidity swings.

The dowels do not have to go all the way thru unless you desire that appearance. They can be done from the back . so as to not show. You still have to engage the material on both sides of the tenon though.
It sounds complicated, but it's not. It's hard to explain though. .
The purpose of the haunches are to increase the strength of the joint and not compromise the strength of the post.