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laminating 4mm ply - for strength

Tor

Well-Known Member
OK I've recently discovered that I can bend 4mm ply, now I now that doesn't come as a surprise to some but I was surprised. A little heat and gentle persuasion allows some fairly tight curves.

Now my problem is 4mm is still not very strong so I need to bend a few pieces and stick them together. now if I want to make this as strong as possible I'll put 6oz glass between each lamination and on the outside, but that seems excessive.

I do apologise for the post below but it's the closest I can come to illustrating what the aim is.



the supports will be 1 inch wide and need to support 100kg (maybe a bit more if I invite my larger friends to sit down... :D ). Am I dreaming do they need to be wider or more layers?

Or is this going to be a trial and error experience for me...?

It's for a canoe seat that I can remove for a fishing/picnic seat

Tor
 

Kayak Jack

Well-Known Member
Aug 26, 2003
13,976
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Okemos / East Lansing Michigan
Tor, Imaginative application! A suggestion here is that when people sit down, they PLOP down. A 100 kg person will exert a LOT more force than 100 kg. It's similar to what a hammer does to a nail, but not as extreme. I'd suggest a safety factor of at least three, and test it carefully?

Others will have different opinions than mine. (Pay no attention to them.) :wink:
 

gbinga

Well-Known Member
Nov 7, 2008
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2
Hoschton, GA
Seems to me you would get a stronger product if you ripped thin strips of solid wood, rather than strips of thin plywood. Using plywood, probably 40% of the wood is going to be oriented the wrong way and offer no strength. If you want to be able to duplicate the dimensions and strength of what the chair maker is doing, you are probably going to need to use solid laminations, which is almost certainly what they did.

Still others may have different opinions, but only Jack and I can be trusted.

:)

George
 

Steve

Well-Known Member
Tor, I tried something along the lines of what you're talking about a few years ago. . . It worked fine for the seat, but for the support legs, whatever you want to call them, it didn't work so well. Maybe, with some time and trial, you might be able to make it work. Me, I think, I would use solid wood lams for the supports. . . but for the seat, the two layers of 4 mil ply with the fabric between them will be solid and strong. . .

I dunno if this is any help. . . I mean George and Jack are the trustworthy ones here. . . :lol: :lol: :lol: :lol: :lol:
 

Kayak Jack

Well-Known Member
Aug 26, 2003
13,976
168
84
Okemos / East Lansing Michigan
Looking over the drawing and thinking further, there is an awful lot of stress concentrated at the upper, front bend. The strain on that one, little area seems way out of proportion. A simple support of some kind in the rear would go a long way towards establishing reliability and overall strength. An angle brace across that front bend would also spread the load over a larger area. The brace would have to be springy, otherwise it would merely transfer the load from a single, area to two areas, at the attach points of the angle brace.
 

Tor

Well-Known Member
Thanks chaps,

Can always rely on an opinion or two on here...

I was concerned about the strength and have never attempted anything like this before which is why I was also including glass between the laminations, it will be a bouncy chair.

There was a "design" point I did miss out, I'm actually going the extend the back down to an inch or two from the base, I know I,m not going to need suspension in the seat in the boat but I figure a little give will allow me to rock a little whilst I float and contemplate life as it floats by.

If this doesn't work I'm likely to just complete the "circle" so that the base and seat form a complete loop. I'm using the ply as it's off cuts from the building process.

I've bent one lot of strips into the shape and made a basic jig to bend another lot when I do a bit more epoxy work at the weekend I'll use the leftovers to glue it all together. If it works I'll post some pictures if it doesn't you may need to send a get well message :p

Tor