How does bend radius affect the strength of a square tube bend (think chair back)?

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I'm new to tube bending and getting ready to order my first machine and die. Thanks to the helpful confirmation in a recent thread, I know what size die I'm looking for.Though I hope to use the bender for many things, my most immediate project is stackable chairs, like this one:As you can see, this type of chair has the back formed by a single piece of tube which forms the seat and then is bent up to form the back.So, as I'm looking at different rotary draw tube bender dies, I'm wondering if the radius of the bend has a significant effect on the strength of the resulting joint? In the case of my chair, I'm specifically thinking of how much flex the back will have it you slouch against it.As a secondary question, any gut feelings on what wall thickness such a chair would use? All I have available is .080", and I'm wondering if it'll be too weak. I could take the cap out of one next time I see a chair like this to measure it, but I don't want anyone to think I'm vandalizing their chairs, lol.
Reply:Re the second question, I just found one manufacturer site saying they use 14 ga tubing, which would be even lighter than I'm getting. So, apparently, no worries there.
Reply:Originally Posted by JasonPAtkinsRe the second question, I just found one manufacturer site saying they use 14 ga tubing, which would be even lighter than I'm getting. So, apparently, no worries there.
Reply:Ok, so back to the original question. Does anyone have any experience to know whether the bend radius would affect (one way or the other) how flexy the bend will end up?
Reply:Originally Posted by JasonPAtkinsOk, so back to the original question. Does anyone have any experience to know whether the bend radius would affect (one way or the other) how flexy the bend will end up?
Reply:For all my benders I have sample bends that I premark every inch. It helps with layout and you would get a feel for the strength.
Reply:The cross bar will also eliminate concern for weakness at the radius.  The spot of concern would be at the connection of the crossbar and legs.
Reply:One thing to look out for when bending square tube is the seam splitting. I was bending some rail pickets from 14ga 1/2" square tube at a 3" radius and was having issues with the weld seam splitting. I can't remember for the life of me which way I oriented the tubing to prevent the splitting but thought I'd let you know that it's something to consider.
Reply:Originally Posted by Sharon NeedlesOne thing to look out for when bending square tube is the seam splitting. I was bending some rail pickets from 14ga 1/2" square tube at a 3" radius and was having issues with the weld seam splitting. I can't remember for the life of me which way I oriented the tubing to prevent the splitting but thought I'd let you know that it's something to consider.
Reply:Most tubing like that on the chair will be indented on the inside of the bend so you don't have a wrinkle bend. I think it adds a little strength too.
Reply:Originally Posted by Welder DaveMost tubing like that on the chair will be indented on the inside of the bend so you don't have a wrinkle bend. I think it adds a little strength too.
Reply:Well, I got my model 32 bender ordered along with a 5.5CLR 1" square tube die set ordered. It's the smallest radius that can bend the tube I have available. I think it's probably a wider radius than most commercial chairs like this would use - but I think those are generally mandrel bent. It will be interesting to get my hands on the machine and try it out!