I have a bit of experience with fibreglass, mainly sticking things to other things and roofing rather than shiny moulded stuff.

Toying with the idea of making a fibreglass cargo bike front box to replace the rotting plywood one.

Anyone have tips on where id start to make a mould or make it without a mould?

Ideally id like a gel coat finish rather than roof type finish

It’s bloody heavy.

Custom motorcycles are a good place to start. I intend to make a seat unit for my motorbike at some point.

Cafe Racer Garage has a few good videos on it and the same technique can be applied to what you’re doing I’d reckon.

I’ve a big sheet of stainless steel, 1mm sheet, must be arpund 1m x 0 6m, free if ye can pick up anywhere near Ayrshire?.

For a smooth gel coat finish, you’ll be best served by making a female mould. The inner surfaces will need to be non-stick so a melamine type facing to the mdf or ply and a two pack filler for the radiused edges. Removal of your grp box will then be made easier by coating the inside of your mould with a release agent.

You could also make and use a male mould but achieving a smooth gel coat finish will be more of a challenge and time consuming.

I’d use carbon, Much lighter and cooler. Much the same techniques. As above, make a female mould to get good surface finish, No need for gel coat, just go for raw carbon.

I’d be tempted to make something from carbon fibre instead because carbon. You could make a form out of ply easily, cover it with something non-sticky and layer the carbon over it. Doesn’t need to be structurally strong so no need to worry about voids and stuff. I think there are vids about that online too.

check out the Easy Composites website and youtube channel. Lots of good guides and a very good range. (not affiliated with them but I buy stuff from them)

I’d be tempted to build another plywood one and get on with cutting about on it.

MAking a fiberglass box rigid is going to be a ball ache and you can screw stuff to plywood…

Could you make it kayak style with light ply and then cover in a layer of fibreglass to stiffen up the corners and waterproof?

Im do a lot of fibreglass work building things like these:

Im just the tea-boy but have the benefit of working with two chaps who know loads about GRP work and have picked up a good deal.

We make moulds with CNC’d foam, but you can do it yourself gluing some 100mm kingspan together, trimming with a knife and then sanding. Then build make up the outer shell with high build 2 pack paints, lots of wet & dry, finish with a lacquer spray and a 600-1200 grit wet and dry.

A bit of mould release/wax to get the damn thing off…

Glue the whole mould to a sheet of glass and you have a workable pattern part from which to make a mould (as we would to make lots of parts – see the green gelcoat, thats a “tool”) or for you, to take a single splash as a final part. You have to think about your finish surfaces – shiny inside or out? Shiny inside you make a shiny block and build over, shiny outside you have to make a big box…in which case use plywood and high build paint rather than dig a hole into foam.

Use gel wax mixed into to gelcoat to the back of your glass if you need an “internal” face which you will for a cargo box really.

Im a couple of beers and a rum into the evening so this probably makes no sense, so drop me a message if you want more info.

EDIT; In case anyone is reading this, we dont make our parts with “bucket & chuck it” chopped strand. We only use that for tools. For parts we use a far more advanced technique…

Stoner has it! Top work dude 😎

Have a quick search for mike Patey on YouTube.
He builds and modifies aeroplanes using carbon fibre and does a lot without vacuum pumps etc. He goes to a lot of time to explain why he does it that way.
Be prepared to lose a few evenings.

More pics stoner!

Op, I would either stick with ply or go carbon. Carbon is very easy to do ime compared to fibreglass, or should I say easier to get a strong final product.

Wow lots of knowledge on here, hadnt thought of using melamine as a mould.

I had thought of using carbon but the cost is putting me off, i may end up having a play around and seeing how i get on with small things first.

Have a look at stitch and glue plywood construction, best of both worlds, just start with some balsa cored plywood to keep the weight down.

Some cool stitch and glue stuff….

International canoe Machete (uses an eggbox internal structure)

Teardrop caravan

Note the use of curved pannels means you can build a rigid monocoque structure