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post #1 of 7 Old 06-15-2010, 08:58 PM Thread Starter
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Outdoor Bench

I want to make a bench for the porch out of some black locust that I'll have milled soon. It will only be 4 - 5' long with a seat and back depending on what the small logs will yield. The basic design is like that of the plastic one pictured.
My questions involve the support members and not the seat ans back. I'm considering using 3x4s or 2x3s (full dimension) for the components. I'm guessing the vertical piece (straight no bend) would be slanted back wards about 10 degrees. The seat supports and the foot would be half lapped to the vertical piece. Each joint would have a recessed bolt and then plugged from both sides. Would this type of joint be strong enough or would it have play in it oner time. I'm not set on this design, I just don't want anything too heavy and clunky looking. Any ideas?
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post #2 of 7 Old 06-16-2010, 10:46 AM
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With the item shown the plastic seats, no cross bracing and no seat arm support my fears relate to vertical and lateral collapse. The seat collapses at the middle from people plopping down and the unit collapses laterally from people sliding onto the unit from the side. It might be OK for small children.

My confidence doesn't rise with that design with wood.

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post #3 of 7 Old 06-16-2010, 11:16 AM Thread Starter
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Sorry, I just assumed you could read my mind. The seat and back will be made out of 2" (finished thickness) minimum slabs, either live edge or not, of black locust. They will be 12-15" wide each depending on what the small logs yield. No plastic involved. Plus, the bench length would only be 5' maximum. That would make the unsupported span across the middle around 4'-6". I would thick that would be sufficient to keep from buckling under the weight of even a fat [email protected]@ like myself.
My concern is the strength of the substructure. I've seen wooden benches before, can't remember where, of similar design. But maybe, the seat support member was mortised into the vertical back member, which in turn was mortised into the foot. Get the idea. I was going to simplify the joints by making them half lap and the bolting them to keep them secure. Just don't know if there will be movement in the joints over time. Any ideas on a different design?
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post #4 of 7 Old 06-16-2010, 12:20 PM
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For the feet I would use two pieces for each foot.
Dado a cross grain recess in the middle of each piece, sized to fit the upright leg/back brace. Like two half laps. Then face glue them together.
I'd use the full thickness and width of the upright to fit in the resulting "mortise". Or, you could make the tenon 1/2" narrower (1/4" off each side). Size the dado accordingly. Use Tite Bond lll or a urethane glue for weather proofing. I always work a couple of coats of glue into the end grain of the tenon, also. You don't want any wicking.
For the leg/back brace, I'd also use two pieces and a looong scarf joint at the bend.
I'm ultra cautious, so I'd make a middle one, too. At least, under the seat.
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post #5 of 7 Old 06-16-2010, 12:39 PM
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djg,
I gathered from your 1st post that you'd be using Locust for pretty much the entire bench. My lateral reasoning stems from the surface area where the (supplied pic) shows the seat and back attached.

The broader the area covered the more fasteners can be used to affix and stabilize the frame to the flat pieces without compromising the structural integrity of the frame or the back and seat. If one were to let in the back and seat to the frame this also would improve stability regarding the lateral movement of the unit, (prevent wracking).

2" thick slabs used for back and seat would hold up to my mother-in-laws FA, but the (supplied pic) shows no vertical/bracing support under the members supporting the seat which no mortise and Tenon will support for long under the kinetic stresses exerted on them by plopping down onto the seat.

Half laps would be fine too in conjunction with the bracing and let-in of the back and seat. If the bench is going to be on the porch you might consider a 3rd frame for the middle and let-in like the sides or a cross brace between the legs to prevent any toeing of the legs and an extra triangle brace up to the seat for the sedentary @$$ that never moves, (dead load opposed to live load) which does move.

Ever consider porch swing?

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post #6 of 7 Old 06-16-2010, 02:26 PM Thread Starter
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Ghidrah,
I guess I'm a little dense, I didn't catch what you were saying. I understand now; I hadn't considered those forces. I think I'll use your idea and run a dado (3/4" deep) up the back to receive each leg assembly. With respect to the seat support, I wasn't sure if what I had planned would be sufficient. Maybe I'll run a short leg to the ground in front or use gusset bracing.
Gene, I think I'll take our suggestion on foot design, it will make it easier.
In the next week or two, I'll be having the logs milled and I want to be sure I have the right dimensions of stock to do my projects
Thanks all.
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post #7 of 7 Old 06-16-2010, 05:05 PM
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djg,
I should have said dado instead of let in, I still use framing think instead of furniture think.
The dado doesn't need to be 3/4" deep with nice square corners 3/8 would be fine. The important part is that the dado locks the frame to the backer and seat like an old fashioned huricane brace on an exterior wall.

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