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Discussion Starter · #1 ·
Basically two pieces of wood, can't get any easier than that. Most of the dimensions online are too narrow, usually 10-12" wide so I thought I could just make it wider and adjust as necessary. Didn't work or maybe I got the wrong kind of wood.

I've done a lot of projects with plain old plywood but wanted this chair to have nicer finish as it is a gift. I spent $50 on a 4x8 sheet of birch 3/4" thick because it said it could be used outside with proper finishing which I took to be polyurethane sealer.

I measured the seat of the Adirondack chair I made a few weeks ago and decided I needed 20" wide seat that goes down to 16" wide when cut to fit inside the back piece.

Cut it out, sanded the edges, put it together and while it was a bit too "high" for me, it will be fine for the recipient except that it broke when I sat on it. I did not flop, I sat down and poof, there it went.
I am 5'4", 145 lb. The recipient is prob. 6'3" and 270 pounds. Thankfully I did not paint the design on it, seal it and give it away for it to break when they sat in it.

So, I need help. Did making the seat wider go against some law of gravity or something so it wasn't as sturdy as if it was narrower? Was the birch just not strong enough? I had not yet cut the edges into angles either for the ends that sit on the ground but I doubt that had much to do with the breaking of the chair.

Please assist if you can. The gift is already 2 weeks past birthday but I just found out they really want one of these chairs and its a quick project except for painting the design which will take me a week to do.

Thanks,
kjh9835
 

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based on the photo

The taller piece, the back is only as strong as the 2 narrow outboard supports....not good in plywood! The chair is designed to be made from planks as you stated, not plywood. Sorry. The thicker the planks 1 1/2" the better. You could double the plywood or use hardwood. I would not attempt to repair a broken joint, just start over. Sorry.
You can use construction grade 2 x 8's and glue them together for a wider chair. It won't be a perfectly smooth as plywood, but much stronger. The issue with that design as I see it is making the cuts at the correct angles. Very difficult to do in that thickness without sharp tools on those angles. What are your shop's capabilities?
 

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When I belonged to the SCA, we made them from 2X10's or 2X12's. They are not intended to be particularly comfortable but yet more so than you would think. The idea is to be able to carry 2 flat boards. I made mine from cypress because it is fairly lightweight. I never bothered with angles because they were meant to used on dirt or grass. Vikings didnt have paved surfaces. I also used it upside down from the above photo with the narrower side on your back and the wider piece on the floor.
Another variation was to make it as in the sketch. This obviously is not drawn to scale.
 

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Discussion Starter · #6 ·
The bottom broke where the "slot" is for inserting the back. It is 2" from the edges and both sides broke. I just skimmed over the posts as I overslept and will be gone til this afternoon. I will check back later today, read them all and give more info.

I do appreciate everyone's help. I figured it was the material (plywood) but I wanted the super smooth surface. I am not even sure what supplies I can get at Lowes/Home Depot/Menards. Lowes will cut it down to fit my car, I don't know about the other two stores.

kjh9835
 

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Discussion Starter · #10 ·
Ok, done with todays stuff, back to chair tomorrow. Yes that is a picture of what I am trying to do but will be painting a face on it when I get one made that is sturdy enough to hold without breaking.

The intended recipient was here today so I showed him the chair, explained why I made it larger and he said the 12" width is plenty as it's not meant to be sat in like a lawn chair but you actually straddle it and lean back.

He has some wood planks I could recycle but they are pressure treated and I read somewhere that you should not use pressure treated lumber. Why is that esp since it will be outdoors? He actually wanted four of them so I figured I'd give him one and he could get the supplies for the other 3 and help pick out the tiki faces for me to paint on the others.

I have other sheets of plywood/pieces from other projects so I'm going to put two of them together for thickness with the smoother birch on top and make the slot narrower instead of 2" from each side. I can also reinforce the back as mentioned.

If that doesn't work, I'll start over with new supplies.
Thanks for the advice, will post pictures when done.

kjh9835
 
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