Calculating Stretcher Length?

[onocoffee]

Okay, finally I got a pic to successfully post!

I'm working on a project that's utilizing an 8 foot live edge bar top that's about 18" deep. Want to build a wood base for it with 2"x2" structure. I'm thinking that the support under the top should be 6ft long and 2"w x 4"h (does this sound reasonable?). The legs will be framed 2"x2" and a lower crossbar with angled supports. I'm trying to figure out how long the angled supports might be (and figure that can find the right length as it's being assembled.

Overall height from floor to the bar top should be no more than 38".

At the moment, I'm trying to understand how long everything should be, and what dimensions they should be, in order to calculate how much lumber I will need. Apologies for the poor drawing. The inspiration for this frame is from Ishitani Furniture:


I would like to mimic the design of the frame, sans the verticals that go through the top and with Dominos to do the joinery.

This will be my most ambitious project to date. The top is pretty much completed and is 1.5" thick white oak that was from a 180 year old tree that fell in our neighborhood three years ago.

I'm pretty inexperienced and have tried to be as inclusive as possible but I don't know enough to know what to ask or what other considerations I need to keep in mind.

And I should add that while the top is white oak, I'm open to other woods for the frame lumber. I've got a very well-stocked lumber supplier not too far from me.

Thanks!

View attachment 1

 

[Dongar]

I think this is what you want. I drew it in cad so it is easy to change if you need different dimension.

 

[onocoffee]

Wow, Thanks [member=978]Dongar[/member] - This is very helpful and I'm very appreciative!

 

[luvmytoolz]

Given there's a lot of weight in the top, if going along the lines of the drawing Dongar supplied I'd make a small change, moving the angled supports as close to the end as possible, and inset them each in the bottom stretcher enough to hold them in place, 5mm or so would be adequate.

This will help reduce undue stress on the bottom stretcher causing it to bow over time.
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[onocoffee]

[member=75933]luvmytoolz[/member]  - This makes sense. In the original, Ishitani joints the supports into the stretchers in a similar manner. Not sure if my skills are up to that task, but I perhaps will give it a try. Thanks!

 

[jeffinsgf]

In the spirit of teaching a man to fish instead of giving him a fish...

The length of your angled brace is "C" in the high school geometry lesson A(2)+B(2)=C(2). "A" is the distance from the bottom of the apron to the top of the lower stretcher. "B" is the distance from that intersection to the intersection of the lower stretcher and the angled brace. Square those two numbers, add them together and pull the square root of the result, and that is the length of your angled brace.

 

[Packard]

Suspect that you could come up with the dimensions without using any math at all.  By simply mocking up the base using the dressed pieces of the selected lumber and marking. You almost certainly could come up with the correct length (even if you don’t know what that length actually is).

I am big on not using rulers.  I use story-sticks often, and when convenient, I simply move the actual piece to the assembly and mark and then cut. 

It probably says more about me (and measuring tools) than about the technique.

And yes, I would use a ruler to come up with the end rectangles as I would need some base dimensions.  But the cross pieces, would be “derived” by either using a story stick (or an adjustable story stick) or if the pieces are light and easy to handle, marking the actual piece. 

I have fewer errors by working like that than the “measuring twice, cut once method.

 

[smorgasbord]

Given there's a lot of weight in the top, if going along the lines of the drawing Dongar supplied I'd make a small change, moving the angled supports as close to the end as possible, and inset them each in the bottom stretcher enough to hold them in place, 5mm or so would be adequate.
This will help reduce undue stress on the bottom stretcher causing it to bow over time.

In my view, the angled members are not structurally necessary: You've got a 1.5" white oak top that's further supported by a 2" thick stretcher just under it, and the legs are only 64" apart, supporting the under-top stretcher and the top. In this case, you really only need the bottom horizontal stretcher to keep the legs from angling out or in - the angled members are decorative only.

So my advice is to size them as to whatever looks good to your eye and remember that having them complicates the glue-up.

 

[Packard]

Given there's a lot of weight in the top, if going along the lines of the drawing Dongar supplied I'd make a small change, moving the angled supports as close to the end as possible, and inset them each in the bottom stretcher enough to hold them in place, 5mm or so would be adequate.
This will help reduce undue stress on the bottom stretcher causing it to bow over time.

In my view, the angled members are not structurally necessary: You've got a 1.5" white oak top that's further supported by a 2" thick stretcher just under it, and the legs are only 64" apart, supporting the under-top stretcher and the top. In this case, you really only need the bottom horizontal stretcher to keep the legs from angling out or in - the angled members are decorative only.

So my advice is to size them as to whatever looks good to your eye and remember that having them complicates the glue-up.

Indeed.  He can even make the stretchers “invisible” using stainless steel cable.  I have black PET clad stainless steel in about 0.040” diameter with about a 50 pound test.  At 5 feet it would be nearly invisible.

I think the bottom stretchers would look better if they were about 1/3 of the way off the floor. 

 

[Michael Kellough]

I'd keep the wood diagonal braces to protect the joints at the top of the legs.

 

[Crazyraceguy]

My two cents would say that, while the angled supports may not be necessary to support the weight that might be placed on such a piece of furniture, they will absolutely keep it from racking.
That is probably the greatest force that this would ever see anyway.

 

[Packard]

I read once that wood posts could hold enormous amount of weight if you can keep them from bowing. 

I agree, racking is the only way this item will fail. 

To obtain a minimalist look, the builder would only need to attach it to the wall.  The wall then becomes part of the structure and racking is no longer an issue. 

There are two sources of racking.  The first is the joint itself.  The second are the legs. 

I don’t think 2” square legs are going to bend.  So, if I were building this, I would concern myself with the joinery. 

I think that chair construction demands the strongest joinery.  A favorite is a through tenon with wedges.  In my mind, that is all the piece needs structurally.  I do think it is best attached to the wall, if only because it could easily be knocked over.