Wedged M&Ts - tapered mortises or not?

As I understand it

jim_reed@marietta

>I do lots of mortices, but have never have the need to do a tapered or wedged one. Here are my thoughts: The strength of the joint is determined by the ability of the mortice to hold its shape and the ability of the tenon to not break. For everything to work, the tenon must stay in place. Glue and wedges are useful only to keep everything together. BUT the joint must not be so strong that it blows out due to wood movement. For that reason, I think wedging should be done only on the last 1/3rd of the tenon. Aggressive wedging could break the tenon and severe dovetailing does not seem to allow wood movement in the joint. I would rather my glue joint fail than have the mortice crack on the side. Just my $.02 worth. Good luck with your project--it sounds pretty ambitious.

Re: Wedged M&Ts - tapered mortises or not?

David Miller from Iowa

>Agree with Jim. Again. Just wanted to add that I have done it both ways, because intuitively it seems like you should taper the mortise. However, when I did so, I had a lot of trouble with splitting coming out into the visble piece. Now I never taper the mortise and have never had a problem with coming loose.

Re: As I understand it

Sean Evoy

>Jim,

So you only cut the kerf for the wedge about 1/3 of the way down the tenon or do you cut it deeper?

Re: Wedged M&Ts - tapered mortises or not?

Tim of San Leandro

>The tapered mortise is for a "dovetail" mechanical lock. It's purpose is the same as the dovetail....keep the joint together after glue failure.

to prevent splitting of the tenon....don't taper too much and match the length of the taper with the angle of wedge. Longer tenons can have larger wedges. Also, placement of the wedge is important. Too close to the edge of the tenon and it won't have strength. Too close to the middle and you'll surely end up splitting the tenoned stick. And drill a hole at the end of the slot that accepts the wedge. Hole should be perpendicular to the slot and allows for the separation of the tenon but prevents the split (the slot you cut is essentially a long grain split) from continuing to propagate along the length of the tenoned stick.

Tim

Re: Wedged M&Ts - tapered mortises Depends

gtools

>(opinion) Most early doors were double wedged (tenon ends) with a tapered tenon. I think the secret was to use a thin wedge and tap it in till it rings solid. (to prevent expansion blowout). If your going to wedge the center of the tenon, V the tenon kerf and drill a hole at the bottom of the V (hopefully prevent a split), match the wedge to the V cut, shoot for a fairly tight fit before you do the center wedge thing.....gtools....

Re: Wedged M&Ts - tapered mortises or not? *LINK*

Adam in Kingston

>There was an article recently in FWW or wedged M&T. Quite a good article on the subject. The author stated that 5 degrees was the magically angle where friction between the wedge and teh wall holds strong (no need for glue. I have done both: taper the mortice if I need extra strength, dont bother for decrative/tight joints.


http://www.adamkropinski.ca

I don't get it.

Adam Cherubini, NJ

>Scott

I don�t get it. Why would you wedge a tenon again? I thought you were talking about tusk tenons. Chairmakers wedge their tenons, but their tenons don�t have shoulders, so that�s not at all similar.

Aren't you choosing the tenon over the shoulder to react load and stay tight?

Isn't draw boring a better plan?

Adam

Kerf

jim_reed@marietta

>Cut the kerf 1/2 and wedge the last 1/3 of the tenon. That leaves a little wiggle room to let the tenon halves move instead of split.

Re: I don't get it.

Steve Kubien

>Looks would be one reason. Using a different colour of wood for the wedges can have a very effect, depending on your taste.

I'll be using wedged thru tenons on my guitar stand. Oh right, I gotta get going on that.....

Steve Kubien

Ajax, Ontario

remove the _9 to email

so tenon doesn't pull out after glue failure

Tim of San Leandro

>

Me either...

Scott in Douglassville, PA

>Hey, Adam -

Was I talking about wedging tenons before? I am, confused...

FWIW, I'm wedging tenons on the rails on the head- and footboards on the bed I'm making my daughter. I'm planning to taper the mortises about 2� or so on each side. This is going to be a stout bed - legs are about 2-3/4" square, rail stock is all 6/4 ash - and I wanted a sturdy joint to withstand the abuse my two year old is likely to give it. It's a full size mattress set, so she'll be in this bed for a while. I could've draw-bored the tenons, but I enjoy making the through wedged M&Ts, they seemed appropriate for this, and I think they'll look spiffy. Hoping, anyway.

Thanks,

Scott

Re: Me either...

Adam Cherubini, NJ

>Scott,

The "again" part was just a way of asking.

I don't agree that the wedged tenons are appropriate for this. I've never seen anything remotely similar. I think when the tenon shrinks (and you are exposing its endgrain to encourgae that), the joint will loosen. A draw bored joint will be much stronger. That's the way you build a joint stools, that's the way early formal chairs were made, that's the way houses were made.

Bedsteads, made to be taken apart, sometimes used bed bolts. The design, while not visually like a drawbore, is similar structurally. Load is taken at the tenon shoulders. That's a recurring design.

If strong is what you want, but you like the look of a wedged tenon, maybe you could do both?

Adam

Something "remotely similar"... *LINK*

Scott in Douglassville, PA

>Now, I know your impressions of FWW and the modern interpretation of workbenches in general, but I'll opine that Lon Schleining is years ahead as a woodworker of where I'll be in a decade; I used wedged M&Ts on my bench base before this article came out, and his use helped my general confidence level in using the wedgies on my current project. The cover image in the link isn't the easiest to see; he used wedges to join the rails to the legs. Take one of those assemblies (two legs wedged to the top and bottom rail) and you've got a good approximation of my head- and footboard designs. The headboard has at least two (maybe three) rails; the footboard, two. Additionally, the head- and footboards will be joined to each other using stub tenons and bed bolts in the side rails.

I'm really not trying to be argumentative here - I really don't understand why using a wedged through M&T is inappropriate for this. I understand the tenon's gonna shrink a tiny bit, as will the leg; we don't see drastic humidity swings in this house, and I'm not anticipating any more of a problem than with any other wedged joint we have.

I be needin' some elucidation...


"The Essential Workbench" FWW #167

Re: Something "remotely similar"...

Adam Cherubini, NJ

>Hi Scott,

Sorry if I haven't been clear.

M&T do different things. One thing they do is react moments. There are two ways a M&T can react moments. In the mortise (imagine the tenon rocking in the mortise) or at the shoulder (imagine the lower shoulder bearing against the upright). Since you can't get both a tight/preloaded shoulder and a tight/preloaded mortise, you have to choose.

Drawing boring preloads the shoulder. As the tenon shrinks in thickness or width, nothing happens to the preload. The upright can shrink, but in the case of barn or bed, the mortise is typically far away from the exposed endgrain, so this will happen slowly if at all. When/if it does the initial change will be loss of preload, followed by rotation.

In your case, you are relying on the dimensional stability of the tenon to maintain pressure/preload in the mortise. But by exposing the end grain of the tenon, you're inviting tenon dimensional instability.

A better, but rarely seen joint is the fox wedged tenon. The fox wedged tenon is just like your design except the mortise is dry (not through). The reason for this is to protect the tenon's end grain.

Protecting end grain is a lesson learned through hundreds if not thousands of years. That there are woodworkers, machining wood like aircraft parts, who ignore this lesson neither surprises me, nor discounts its relevance.

Adam

P.S. I'll be away on vacation for a week so if I don't get back to you, good luck!