# lumber thickness for bench



## harum (Nov 25, 2013)

Hello, was wondering if I could use 4/4 lumber, meaning 1"-thick, for a mid-century Danish style entryway bench with splayed legs and loose tenon joinery. The legs are splayed out to the sides by about 10°. There are two pairs of stretchers connecting the opposite pairs of legs. The seat is going to be weaved and the seat frame is 30" x 15".

The sag calculator says that load-wise if build out of 1" x 1-1/2" lumber this seat would strong enough to support 400 lbs.

I guess my question is: Would loose tenons joining 1"-thick lumber be strong enough for splayed legs?

The mortises joining legs to seat would be 1/2" wide, 1-1/2" long and 1-1/2" (in each direction) deep.

Hope my question makes sense.
Best wishes, h.


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## rwe2156 (May 7, 2014)

Pic would help. Is there an apron or is the seat frame mortised into the legs?

Pinning tenons adds a lot of strength.


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## verdesardog (Apr 2, 2011)

An apron under the seat would increase the load bearing ability tremendously…I made a 6' bench with 4/4 barn wood with a 4" apron, it can be sat on by as many people as can fit and there is no sag.


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## Lazyman (Aug 8, 2014)

I don't understand your description. Not sure how you would have 1 1/2" (in each direction = 3"?) tenons joining 2 1" thick boards (seat and legs)? Do you really mean a spline? It sounds like you are going to make a frame out of 1 1/2" boards and weave a wicker or cord seat? Are the 3" tenons for joining the frame perhaps?

Are there 2 legs the entire width of the bench or are there 4 and what width? How are you planning to attach the stretchers to the legs?

I agree. A rough drawing or picture would help.


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## harum (Nov 25, 2013)

Thank you for the responses! Yes, I guess my description didn't give all the details.

Three pictures below is my rough model based on David Larch's Mid Century Bench. The overall dimensions of the model: 42"W x 22"H x 14"D.




























There is no apron; the legs are mortised into the seat frame. Because of the slot for cord the effective seat frame is 1-1/2" wide (meaning, top to bottom)-still there would be no visible sag under 400 lbs even with 1"-thick seat frame according to the sag calculator. I was wondering if 1" thickness would be strong enough for the joint between the splayed legs and the seat frame.

Thanks for the photo, verdesardog!



> Pic would help. Is there an apron or is the seat frame mortised into the legs?
> 
> Pinning tenons adds a lot of strength.
> 
> - rwe2156


Thanks! Yes, legs are joined to the seat. WIll consider this.



> I don t understand your description. Not sure how you would have 1 1/2" (in each direction = 3"?) tenons joining 2 1" thick boards (seat and legs)? Do you really mean a spline? It sounds like you are going to make a frame out of 1 1/2" boards and weave a wicker or cord seat? Are the 3" tenons for joining the frame perhaps?
> 
> ...
> 
> - Lazyman


From the model, the leg-to-frame loose tenon can actually be even 2" in each direction. In the model I used 1-1/2" thick lumber which makes the bench look kind of bulky, so I want to understand if using 1"-thick lumber changes anything in terms of strength.


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## Lazyman (Aug 8, 2014)

A picture is worth a thousand words. While I think that 1" thick would probably work okay, the overall structure will keep it together, having only 1/4" on either side of a 1/2" tenon would make me want to keep the thickness at 1.5" or at least make the tenon thinner. I actually like the proportions in the drawings myself. I think that you want the seat to look like it has a enough bulk that a 250 pound person can sit on it. Note that the sagintor is for a static load not impact of someone sitting down. Remember that a heavy person plopping down has gravity helping so I wouldn't be surprised if there was a moment of stress greater than 400 lbs at the point of impact (though I didn't do any math to verify that assumption).

As long as your stretchers are well attached, the loose tenons to attach the legs to the seat will be plenty strong but if you want a little extra strength, you could drill a hole through the tenon for a dowel after you assemble the joint.


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## harum (Nov 25, 2013)

> ... As long as your stretchers are well attached, the loose tenons to attach the legs to the seat will be plenty strong but if you want a little extra strength, you could drill a hole through the tenon for a dowel after you assemble the joint.
> ...
> 
> - Lazyman


Thanks! Yes, haven't thought about static load vs. real person plopping down, shifting weight, leaning back and forth, etc.

Thinking out loud… the 1/4" outside of 1/2" tenon should not receive much stress, unless the bench is tilted on its front (or back) legs. Rather, almost all stress will be applied in the perpendicular direction pulling the legs to the sides and up-this is what thicker tenons, wider legs, and stretchers should take care of. Sounds like the only benefit of going from 1" to 1-1/2" thickness will be only thicker outsides of tenons, 1/2" vs. 1/4", which is, however, really important in dealing with the stress from "rocking".


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## MrRon (Jul 9, 2009)

As I see it, everything will work as designed. The only problem might be that the 4 legs are of equal length and the floor they rest on is flat to prevent rocking. That could stress the joints.


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## harum (Nov 25, 2013)

This an adjustable-width model made of 3/8"-thick cut-offs and held by glue and a few clamps. While it survived my carefully sitting down on it, I found that the height of 22" is too much for an entryway bench. Got to go with 17-1/2", exact toilet height.


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