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Apron to leg joinery for bench

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Forum topic by CrankAddict posted 12-14-2020 05:27 PM 637 views 0 times favorited 19 replies Add to Favorites Watch
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CrankAddict

139 posts in 1019 days


12-14-2020 05:27 PM

I’m looking to build a bench that is 48” wide, 18” deep and about 20” tall. The legs will be a tapered, splayed (5 degrees in both directions) mid century style. My question is whether or not this type of M&T joinery will be strong enough or if I need some additional way to anchor the legs to the aprons? I made the tenon from the longer apron the deeper one, figured it would have more stress. But is this good enough?

Thanks for looking!

Jeff


19 replies so far

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Madmark2

3063 posts in 1805 days


#1 posted 12-14-2020 05:32 PM

Bench? As in to be sat upon? Umm 48” wide invites two to sit. Worst case ~250# x2 for 500# dynamic load. Safety factor should be 100% for dynamic loading. Each leg will have to resist two fat asses plopping down hard. There is a reason you don’t see a lot of splay leg benches.

Looking at your diagram it looks like a 1/4” tenon on the end of 3/4” stock to carry that weight. Would you trust it?

You didn’t mention wood. Pine? Oak? Jatoba? Ipe? It make a difference.

Your leg length & hence lever arm, is 1-2/3 greater at 20” than the (eyeballing here) 12” or so legs on your example. Note the “heaviness” of the legs in your example.

-- The hump with the stump and the pump!

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CrankAddict

139 posts in 1019 days


#2 posted 12-14-2020 05:36 PM

It’s a “telephone bench” so seating for one, then a drawer for storage. Basically a custom version of this:

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Fred Hargis

7198 posts in 3710 days


#3 posted 12-14-2020 05:40 PM

It looks ;like your tenons are the common “1/3 of the workpiece thickness”. What if those tenons were 1/2 of the workpiece?

-- Our village hasn't lost it's idiot, he was elected to congress.

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CrankAddict

139 posts in 1019 days


#4 posted 12-14-2020 05:45 PM



It looks ;like your tenons are the common “1/3 of the workpiece thickness”. What if those tenons were 1/2 of the workpiece?

- Fred Hargis

You are correct, and yes when I got to looking at that screenshot they do look a bit skinny at only 1/4” (aprons are 3/4” thick as drawn, but nothing is set in stone at this point). I can imagine ways to strengthen the apron perimeter (45 degree gussets at each corner, etc) but I’m not sure how else to strengthen the apron-to-leg joint other than larger tenons.

View LesB's profile

LesB

3062 posts in 4660 days


#5 posted 12-14-2020 06:20 PM

The only addition I can see to strengthen the joint is to use wider apron and either a wider tenon or split into two tenons.

-- Les B, Oregon

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BuffaloBrewer

79 posts in 2035 days


#6 posted 12-14-2020 06:32 PM

how much strength would pinning the joint add?

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CrankAddict

139 posts in 1019 days


#7 posted 12-14-2020 08:39 PM

I wondered about pinning too, but doesn’t seem like there’s a lot of meat to get the pin in since the tenons don’t go that deep. It is looking more robust with 1” thick aprons and 1/2” thick tenons…

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CWWoodworking

2121 posts in 1396 days


#8 posted 12-14-2020 08:42 PM

Glue in some corner block and your fine.

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CrankAddict

139 posts in 1019 days


#9 posted 12-14-2020 08:59 PM



Glue in some corner block and your fine.

- CWWoodworking

Can you expand on this a bit? If the inside corner was a 90 I can imagine putting a block in there, but with this design there is no obvious surface to glue it to. What is the actual goal here, to make the apron perimeter more strong (which I could do a 45 degree gusset) or to actually tie the leg to the perimeter better?

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CWWoodworking

2121 posts in 1396 days


#10 posted 12-14-2020 09:17 PM

With that setup, you could modify the leg so everything would be at 90 so the glue block would fit in nice. Or make a jig to make the block fit the corner.

3rd option would be to run a cross brace that spans over the funky corner and basically ties the aprons together. This would be the weakest but better than nothing.

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CrankAddict

139 posts in 1019 days


#11 posted 12-14-2020 09:26 PM

Yeah it would be easy enough to flush that outer corner of the upper leg and make it an inner corner. I just wasn’t sure how much it would really stabilize the leg just bonding to that one sliver of it. I guess I could always build and glue it up without anything extra in the corner, then sit on it and see how much extra it takes, if anything, to tighten it up.

Do any of you have a guess on how the commercial furniture that looks like this (like I showed above from West Elm) is tied together? I’m guessing some kind of metal fasteners?

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CWWoodworking

2121 posts in 1396 days


#12 posted 12-14-2020 09:34 PM

They all will have a corner block. Most would have a lag screw/bolt going into the leg. Bolt if it’s KD.

I would just clean up the corner to make it easy for a block and put it in. It’s cheap and fairly easy to do.

View SMP's profile

SMP

4734 posts in 1122 days


#13 posted 12-14-2020 09:50 PM


They all will have a corner block. Most would have a lag screw/bolt going into the leg. Bolt if it’s KD.

I would just clean up the corner to make it easy for a block and put it in. It’s cheap and fairly easy to do.

- CWWoodworking

Or sometimes they will have hanger bolts on the legs that fit through holes in the corner blocks and then attach with washers and nuts.

Edit:
Found their assembly instructions so you can visually see what CWWoodworking is talking about:
https://assets.weimgs.com/weimgs/ab/images/i/202048/0049/images/pdf/assembly-instructions/english/Mid-Century_Storage_Bench.pdf

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Fred Hargis

7198 posts in 3710 days


#14 posted 12-14-2020 09:51 PM

Well, I've used these in the past and they add a lot of stiffness to the joint, and you might get them to work with splayed legs. You can check the instructions and see if you think they might work.

-- Our village hasn't lost it's idiot, he was elected to congress.

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CrankAddict

139 posts in 1019 days


#15 posted 12-14-2020 10:54 PM

Thanks for the input everyone. Good find on the West Elm instructions, SMP, I should have thought of that!

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