Fibreglass question

[RazMan]

I need to cut a hole in my kit car bodywork to allow access to the filler cap (the engine bay cover hinges down on top of it at the moment) To avoid having a raw edge visible and to give the panel better rigidity, I need to add a return edge to the cut hole - probably about a 15mm edge should do it.
What is the best way to add this return?

Do I form up a thin fibreglass (chopped mat) ring and bond it to the underside or use strips of matting and finish up with filler?

Any advice will be appreciated

[GreenV8S]

I'm visualising you trying to build up a cylindrical wall around the hole. This would be quite difficult unless you make a former up first, which all looks like rather a lot of work. Can you get away with just epoxying a half inch thick piece of wood behind the hole and cut the hole through both layers?

[RazMan]

Yep, ideally it will be a cylindrical wall. I don't really fancy using wood - rain water would destroy it in time wouldn't it? I suppose a slice of plastic bottle might do the trick but plastic will probably go brittle and it needs to be fairly strong so it will stand up to bodywork stresses / vibration etc.

If I was to wrap a section of plastic bottle in thin strips of mat & resin, I could build up a kind of fibreglass washer, say 5mm thick to bond to the underside. Would that work?

[speedy_thrills]

RazMan said:

I don't really fancy using wood - rain water would destroy it in time wouldn't it?

Not if it’s treated to H5 or H6 standard and you use a decent adhesive.

[RazMan]

Update: I used a plastic water bottle as a former (covered in packing tape to prevent sticking), stuffing it throught the neatly cut hole and taping in place. I then applied chopped mat & resin to the underside, creating a radius where the resin met the existing fibreglass.
When cured, I simply removed the bottle and trimmed the edge with a powerfile. The result is a perfectly formed return edge.

Sorted