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mortise strength

Posts

mortise strength

#1

mortise strength

Cameron

I started cutting mortises for my workbench legs and stretches yesterday and after making the 1st one I started to get nervous on how much material I was going to be removing. I drew up a full sized sketch to visualize the mortise cross-section (sorry it is on a scrap of rosin paper I had at hand). As the tenons are cut they are 3.5" long, 1.5" thick. My legs are 6" x 4 5/8". If I cut the mortises as planed it will end up with the two holes converging, leaving ~1" of the end of the side stretcher's tenon touching nothing. I suspect this isn't too big of a deal for side stretcher strength/racking but I also will end up with a 1.5" x 3 5/8" L cut out of the inside of the leg. I thought about cutting the tenons down to either the green 3" to ensure the mortises do not connect or just drop the side stretcher down to the blue 2 3/8" line which would but it up to the side of the front mortise. Knowing that a M&T gets its strength in the length I am hesitant of cutting them shorter. Am I making a mountain out of a mole hill here? Any suggestions?

Thanks

Re: mortise strength

#2

Re: mortise strength

Bill Tindall, E.Tn.

The mortise you have drawn would be adequate for a bridge or log barn. Shrink the thickness. Could you imagine ever breaking a 1/2" thick tenon?

Re: mortise strength

#3

Re: mortise strength

David Weaver

agree with bill. I suspect you're thinking of the strength of the wood imagining that you could bend the tenon.

Try bending a tenon of that size where it emerges above the shoulder.

Remember that no matter what you do, you could literally hollow the top of your legs and glue another tenon in, so it's not like you will break something and bet out an entire bench.

As ridiculous as it sounds to imagine making a lose tenon that needs to be glued in to be fixed, I can make that comment, because you'll never break them.

Recall as I mentioned my tenons are only 2" high and they're something like 3 1/2" square. I imagined ways that they wouldn't be tight enough and then once I got them in realized that I could do little to move them. The times the stretcher wedges have come loose, I have never even noticed it. I use my bench pretty hard, sawing across its width with hand saws, etc, and planing across it, and it's only 22 1/2 inches wide (so it has plenty of excuse to rock). Bill's mentioned effect is noticed - I built it like a building even though it really wouldn't have needed it.

I considered it more of a timber framing exercise, anyway, but I know many take pride in their benches and I don't. I just need something that can take a beating and have its surface refreshed with a scrape and go at it some more.

Re: mortise strength

#4

Re: mortise strength

Keith Newton

Cameron, I’m not sure I’m following all that you stated, but I was wondering if the long stretchers will be half way down the leg supporting a tool shelf. If so, I would raise the short side stretchers up so their bottom is even with the top of the others. Nothing says they have to be the same level.

On the last couple that I built, I then made drawers that fit between the legs and pull out from the end. The drawer fronts align with the long rails and look like they would be structural.

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