do I need shoulders on my workbench tenons

Re: do I need shoulders on my workbench tenons

Bill Tindall, E.Tn.

Evan a small shoulder vastly increased the ability of the M&T joint to remain ridged. A shoulder is so easy to make I would never be without one.

Even in bookcase shelving, if the shelf is made with a single 1/8" shoulder the assembly will be so ridged a back is unnecessary.

I made a loft bed with 5' legs and shouldered rails. It is rock solid. Ditto bunk beds.

Re: do I need shoulders on my workbench tenons

Ellis Walentine

Mortise and tenon joints, from an engineering standpoint, comprise two main things: tenon glue surfaces, and shoulders. The shoulders, as Bill says, impart rigidity in the direction perpendicular to the edge that the shoulder is on, so four shoulders will be rigid in both the X and Y directions; the tenon glue surface is what holds the joint together (and the shoulders tight) in the Z direction. The only other engineering variable is the section modulus of the tenon itself, which needs to be beefy enough to resist a major force which could break it in a worst-case scenario,

however unlikely.

For workbench legs, I would definitely have at least minimal shoulders on all four sides of your tenons. The force of hand planing on a workbench is longitudinal, along the long axis of the bench top, so shoulders are actually more important there than in the front-to-back dimension.

My 2¢,

Ellis

at that size...

David Weaver

...I doubt you'll need them, but a 1" shoulder would be nice for assembly and alignment and may allow you to make the legs flush with the front.

I have a bench with 5 1/2" square laminated ash legs. It's rigid enough without glue and without stringers to play with and across its length. That's a nice thing. I still have the legs tied together with stringers in both length and width (at the bottom), and the length-wise stringers are wedged so that if I ever move, I can take the bench apart into movable pieces.

When the wedges come loose (from hammering or whatever else) I don't ever actually notice that they have in use.

My tenons do not go through to the surface of the bench, either. They are about 2" tall and the bench top is about 4 1/8" thick. It works well.

I'd shoulder them. If you don't like using hand saws, then mark the cuts and make them with something else and split the tenons off. Work at this size is timber framing and not really fine cabinetmaking.

Flush front legs are important in my case because I resaw at the bench and have a leg vise. The leg vise can then grip work pieces without any other gadgets involved (no clamps or shims or any of that nonsense). It allows for faster work, but folks who prefer a skirt to clamp from the underside, that's definitely lost right at the legs.

Re: do I need shoulders on my workbench tenons

Barry Irby

I agree with everyone who says shoulders are important on tenons. Without shoulders the mechanics of the joint are different. Without, you are twisting the glue joint. With shoulders you are trying to extract the tenon. I did some experiments to test this. Made some in pine and the difference was significant.

Have you considered gluing your laminations to create tenons with out sawing them?

Re: do I need shoulders on my workbench tenons

AZ in Colorado Springs

I'd definitely use shouldered tenons. More rigidity.

Re: do I need shoulders on my workbench tenons

John McGaw

Maybe I'm thick (it wouldn't be the first time) but reading your question over and over it says to me that you are running the legs through the top. Is that right? Is there any other structure, stretchers or aprons or braces, involved in the bench? If you were to cut shoulders, where would they be cut? Into the bottom of the ash top the full size of the leg or what?

Personally, if I was running massive through tenons into a massive top I'd at least be wedging them but maybe that is just personal taste -- I like through wedged tenons and have used them quite a few times. They are hard to beat for permanent fastening.

Re: do I need shoulders on my workbench tenons

Cameron

I will have M&T'ed stretchers all the way around the bottom and across the width at the top (shouldn't need length-wise at the top as the ash is plenty thick to negate them...) The leg construction I was planing on can be envisioned by gluing up a 3 board lamination where the middle board is 4.5" proud of the the outer boards, hence shoulders along the length. To clarify my question, I was wondering if I needed shoulders across the width of that tenon, I've got plenty of material there and based on the responses it looks like I will be including shoulders on all 4 sides. I've never done wedged tenons, seems reasonably straight forward but if I mess it up it looks hard to fix, hence my hesitation. I wonder how much wedging brings to the table versus a straight through tenon that is ~1.5" x 4.5"...

Re: do I need shoulders on my workbench tenons

John McGaw

Wedging is useful but can be pretty much a one-way street. This is good for strength but bad for repairs. The thing to remember with tenons the size you are considering is that you will need more than one wedge in each and that, for real strength, you need to taper the mortise to allow the tenon to "spread out" into the gap making the end wider than the root -- hence the one-way description. By all means, skip the wedges on a joint that big if it seems intimidating -- it would be overkill since there will be plenty of other structure for strength.

Now that I understand better your construction method, shouldering the tenon will be a simple matter and, for that reason in can't hurt.

I made a free-standing bookcase that is held together solely by 30 through wedged M&T joints. After a couple of decades of heavy use it is rock solid even though it has no back or other supporting structure.

I'd avoid wedging

David Weaver

with legs as large as you'll have, the bench top will sit on the legs and you'll never notice they're not wedged. I don't think wedging offers an advantage (and did I read correctly that they will be wedged blind tenons?).

Just make them the tiniest bit snug and you'll never have a problem. No wedges.

If you want to tie all of them together and make them more secure, run stringers between the legs at the bottom and wedge them.

Yes you do......

roger lance

I know you have decided to have shoulders all around your legs......that is the proper decision.

With all due respect to Ellis, if you are planeing rough stock....ie flattening.....you'll also be planeing across boards at 45* plus and relying on those shoulders to help fight racking in that direction.

Re: I'd avoid wedging

John McGaw

They were described as through tenons. I'd never suggest blind wedged tenons to anybody as there are way too many ways it can go all pear-shaped. I've looked at the technique carefully and I'll certainly never try it myself as my joints never fit right the first time and with blind wedges there is no going back. Shudder...

Re: I'd avoid wedging

David Weaver

Thanks for the correction. I missed that they were through.