onthefly

I can't for the life of me find the thread about people using plastic gallon milk jugs melted over forms but what I'd like to do is do better on cutting my cowls. They always look terrible (to me). Could I melt some kind of plastic over an ARF fiberglass cowl with the oven or heat gun and then use it as a trial cowl fitting? Would the heat hurt the fiberglass cowl? Would the plastic come off? Any ideas?

MR Flyer57

Dickybird was using plastic soda bottles to make cowls with. I have been trying this out and with my discovery of very large soda bottles you might get something that will work. I have only seen one plane using a fuel bottle for a cowl, and it
wasn't the greatest looking thing, but it was better than nothing.
I don't know if you could use the fiberglass cowl as a plug, because the plastic is sometimes very hard to get off and you might damage it in the process, also the plastic might put enough force on the plug to damage it. I really don't know how much force is put on the plug by the shrinking plastic, but that stuff really holds on to the plug. He suggested using compressed air to lift it away from the plug and get it off.
MR Flyer57

BykrDan

I don't think fiberglass will hold up under the heat of the forming process - I was trying something similar, by molding plastic over a wood plug in the oven.

The wood wasn't holding up in the heat, so I quickly took a lead casting of it by just pressing it into some very lightly dampened sand, which worked perfectly.

Can you get a lead casting of your cowl? I get my lead free from an auto repair shop in the form of discarded wheel weights. They'll melt with a propane torch, but that can take some time - here lately I've taken to just dumping them in a pot, building a nice fire in the backyard, and leaving the pot in the hot coals for a while. I have the sand impression very nearby because you don't want to have to transport the lead very far at all.

Do be careful - molten metal can be DANGEROUS!

foxx

My Feedback: (2)

BykrDan have you considered plaster instead of lead ? it may be safer and easier to lift. I like to try your method if I can find some foundary sand.

toy264

I'll second that. The vapor is toxic, cumulative, and especially dangerous to young childeren. Back in the fifties several comanies, Sears among them, offered lead casting kits for making toy soldiers. Heavy metal poisoning lawsuits got them pulled from production. At the very least, keep the kids away and stay upwind.

BykrDan

Thanks for the tips fellows - I was thinking primarily of the danger of pouring the stuff on a bodily part, but now that you mention it, it does give off a distinctive, noxious smell, too.

It didn't occur to me to use plaster; I've just never bumped into it commercially. Plus, I wasn't sure how it would hold up in heat, either.

For casting the lead, I didn't exactly use "foundry" sand. I grabbed a bagful or ordinary, kids' "sandbox" sand. It leaves a rougher, cast surface, but that just means a little more sanding on the finished part. I filled in some low spots with Bondo, too (which, if you're wondering, holds up just fine in the oven).

Dan.