Marine plywood or form plywood for a cargo bike?

[Kallebo]

Came across a rotten cargo bike yesterday and thought about building a new box. I've always thought that formplywood would be perfect, but when I look around, most people recommend marine plywood. However, it's 4 times more expensive, so I'm seeking advice from you.

Does formplywood work or should one go for the marine option when putting in the effort to make something good? Is there an intermediate alternative? Formplywood with waterproof glue?

 

[Liteavvarje]

Formplyfa is used for casting and withstands moisture and is very strong, I have a sheet myself that has been outside for a couple of years, it hasn't separated in the material, but keep in mind they weigh quite a lot so the car becomes heavy, maybe a lighter sheet and paint.

 

[Johan Gunverth]

Bodywork plywood can be an option. It's also referred to as wear-resistant plywood and deck plywood. Fredricsons in Arlöv is a wholesaler, but from what I understand, they are open to private individuals a few hours a week. http://www.fredricsons.com/upload/Fredricsons_sortimentslista-2016_webb.pdf

 

[Liteavvarje]

Bodywork plywood is very heavy too, the same as I have on the trailer.

 

[Kallebo]

Is it easier to shape formplyfa, or does form just mean that you can build straight forms?

I'm thinking I should be able to reduce the weight by using 9 mm on the sides.

I'll check with the lumberyard to see what they have and can bring in, otherwise fredricssons was a good tip.

 

[Liteavvarje]

It is not possible to change any disc at all, they are more or less rigid, you should probably grab a disc whatever it might be, physically to feel the weight and possibility of using it.

 

[Kallebo]

Bodywork/wear plywood is available down to 6.5 mm thickness and then weighs only 4.7 kg/m2 compared to 8-10 for 12 mm

 

[Marsman80]

It is not possible to alter any board at all, all are more or less stiff, you should probably grab a board, whatever it may be, physically to feel the weight and the possibility of use

Thinner plywood boards can be bent a little and mostly in one direction (depending on the directions of the layers). So if you want it 8 mm thick, you can take 2 pieces of 4 mm and mount them on top of each other to achieve a rounded shape.

 

[Kallebo]

Went to the lumber yard today to survey a bit. They have 4 mm (also 7, 9, and 12 mm) pine plywood that, according to the seller, is glued with water-resistant glue at a reasonable price.

With what radius can you expect to successfully bend two sheets of 4 mm plywood? Would it be possible to bend the sheets around three sides of the box (two corners) with a radius of 15-20 cm?

 

[Liteavvarje]

It's probably doubtful that it will work, seems pretty abrupt, sometimes steam is used to bend wood, but I don't think you have that, haven't done it before with bending boards.

 

[Kallebo]

Hmm. Want it relatively abrupt. Perhaps it can be solved with more parts. It would be nice if the whole box could be strapped together with two parts, one running like a U on the sides and back, and one that forms the bottom and front...

Edit: Doesn't seem impossible... what should I use to glue the panels when I've bent them? I guess Biltema's waterproof wood glue is not recommended. On the American sites I've read, the West epoxy system is recommended. What is the Swedish equivalent?

 

[Kallebo]

I imagine it should be along these lines. But in one or two paragraphs.

 

[Liteavvarje]

Wonderful molds
I don't want to make you sad, but that type is form-pressed laminate and probably needs somewhat heavier machinery for it, have seen on video how they do it.

 

[fsn]

Thinking I'm aiming for something like this. But in one or two pieces.

No, you won't sort that out with plywood. Make a square box instead. Or build an elegant mold and hand-lay a nice fiberglass tub.

 

[Ljus]

Hmm. Want it to be relatively abrupt. Maybe it can be solved with more parts. It would have been nice if the entire box could be tightened together with two pieces, one running as a U on the sides and back, and one forming the bottom and front...

Edit: Doesn't seem impossible... what should I use to glue the boards once I've bent them? I guess Biltema's waterproof wood glue is not recommended. On the American sites I've read now, the West epoxy system is recommended. What's the Swedish equivalent?

West system epoxy is available at well-stocked boat accessory stores here in Sweden. But if you don't need their various useful accessories, regular epoxy from, for example, Biltema works almost as well and is easy to get hold of. If you're anyway planning to protect the entire construction with epoxy, you can choose plywood that is not cross-laminated but where the fibers run in the same direction in all layers. Then it's easy to create a nice radius.