Making Epoxy/Glas/CF parts

I recently finished making a mold for the cowl I'm using on the new plane. Somewhere along the way, I decided that having a CF/epoxy cowl would be cool. Hmm... Well, it seemed like a good idea at the time.

Anyway, since the cowl has a lot of curves and undercuts, I decided that using a silicon molding material would be best. That way (I thought) I could pull the plug out of the mold. I'd never get the plug out of a hard mold. Well, in spite of really greasing the plug down, I found that I could not get plug out. This was when I thanked providence that I had decided to make the mold out of balsa. The plug was made from balsa, sanded to a semi perfect fit and coated with epoxy. then sanded some more and smoothed to a gloss. I don't know if it was the undercuts or just bad conditions (it was a bit cold in the shop), but whatever, the plug was stuck solid in the mold. But since it was balsa, I was able to basically pick the mold out, a small piece at a time.

So, 3 hours of picking and nibbling and the plug was out...in about a million pieces with no damage to the mold, surprisingly. I suppose there's no reason to keep the plug anyway, once the mold is made it's pretty useless. So, tonight I'll lay up the cowl. But if I had know I was going to have to pull the plug a tiny piece at a time, I would have just used hard molding material. It would have made picking out the small pieces easier since it's areder to damage the hard polyester that the comparatively soft silicon.

Oh well, live and learn.

AH Randy.

You needed to put a release agent on your mold. This is a must. Tap Plastic's carries the product. OR call Windy and have him send you the tape on molding CF Parts.

Scott(sorry for mess it makes)Riese

Scott,

I know, and I did. A buch. Along with mold release wax prior to the release agent. Sigh... that's ok, it came out pretty well in the end.

>I recently finished making a mold for the cowl I'm using on
>the new plane. Somewhere along the way, I decided that
>having a CF/epoxy cowl would be cool. Hmm... Well, it seemed
>like a good idea at the time.

Bill Wilson uses foam for plugs. Just plane old foam. Then covers the whole thing with aluminum foil and grease. Works good. Cheap and easy too..

HE uses foam just for the reasons you describe. The plug will "bend".

Splitting the cowl into halves might be good too.

Randy,
I've seen a lot of your cowls over the years and with all the scoops, holes and rakish styling, you should have done a two piece hard mold. I use Smooth-On Mold Max 40 and there is no way you could flex it enough to remove a real complex shape without it tearing. Besides, laying up the carbon in the thing would have been a real
bear to do. Almost impossible to do without a whole bunch of voids that would need filling later. I have enough trouble with the front of the radial cowls for the Sportster and Sukhoi.
Alan

Alan,

You need improved technique.

I've good luck with keeping voids out. And this cowl is pretty smooth, as things go. The back part is undercut (the part that faces the tank compartment) and this made it tough to get out, I think. As I said, if I knew I was going to have to pick the plug out a piece at a time, I would have just made a hard mold.

Randy,
You obviously haven't tried getting 5.7 oz carbon to stay in a tight radius without using a balloon to put pressure against the cloth to the mold.
Alan

Alan,

That's where I use itty bitty pieces. The last lay-up I did I used what amounted to ground up CF in corners and edges with longer pieces on the long curves. I didn't have any problems with sticking, but hey. the night is young.

Hi Randy:

I'm curious as to the silicone molding material you used. I've used quite a bit of Dow soft and hard and the only thing it will stick to is itself. Never used any mold relaeas except on areas of a two piece mold where the fresh pour touches the cured parts of the other half. Never had any stick at all.

Now non-silicone mold materials are a different story. I like wax and PVA.

Cap,

I used Tap Plastics Silicon Molding rubber. Resists tearing really well, but can stick to the plug. Especially if you can't rock the plug a bit to break it loose. Unfortunately, when I went to take the thing apart, I broke the plug loose from the base or I might ave been able to rock it around some and unstick it.

Next time, I'm going to build the molding box a bit differently to allow me to move the base of the plug around to unstick it.