[quote=charlescarlis]A few important notes if you're going to try this:
1) the equipment - you can likely use a $100 vacuum pump from HF or from on-line that are used for vacuuming down air conditioners. People have used them successfully, but they are oil filled and the exhaust will have oil mist in it. That oil mist can be a problem if it gets in your layup. A check valve is really important there, so you contain the vacuum and it doesn't leak through the pump. Mine happens to be a dry rotary vane pump that I picked up a long time ago pretty cheap used. It's great, but not necessary. The rest of the system is basically an air compressor - just in reverse. There's a vacuum switch that is on the tank side that senses the vacuum of the tank and switches the motor on and off - exactly like a compressor. You match up the amp rating to the motor you're turning on and off. I'm using Airtrol brand stuff from Orange Coast Pneumatics, along with Airtrol regulator. To re-build this system, I think i was just over $100, not including the vacuum pump which I had. The fittings are Festo-type, which they call "one-touch" to avoid the issue of brand name. Then cheap-o nylon tubing to fit. Had the vacuum gauges, but they're not expensive.
2) The epoxy is standard West systems, with the vacuum layer being standard resin and slow hardener, with the Hot Coats being resin with Crystal Clear hardener, to fight the UV. When I do the ext 2 rudders, I'm going to tint the first batch with black and then use that to butter up the wood core. In this one, the core was buttered up with un-tinted epoxy. The reason is that the carbon cloth tends to pull and open the weave while in the bag. So far, not a problem in the finished product but you can see through the weave before hot coating if you look very close. Hot coats seem to resolve that though.
3) Make SURE you have all your cloth cut, including reinforcement patterns. The reinforcement patterns printed through the carbon and you can see the edges- sort of; gives it a kind of chiseled look. The airfoils, though are perfectly smooth, so this will have no impact on performance. Just cosmetic, and really not bad.
4) When doing the "hot coat", you need to be sure and do the second coat before the first kicks past the "B" stage - do it while it's very tacky; leaves a finger print kind of thing. If you wait until it fully cures, you'll have to wash the thing first, then sand it (in that order) to get rid of any amine blush. Otherwise you COULD get horrible fish eyes...been there, done that. In this case, the garage was at 65F, the epoxy was at about 69F; I mixed until thermometer hit 72F-73F on the epoxy, to ensure it was kicking. Took about 2 hours to get to solid B-stage. Second layer on will take at least 25% more epoxy resin as it goes on thicker. First layer, you need to brush out bubbles for the first 30-45 minutes and maybe use a heat gun on low to encourage the bubbles to move up and out. I'm doing this one flat, one side at a time; so will take 2 days per rudder before final finishing as opposed to hanging them and doing the entire thing at once. I wanted to be ensured an even coat.[/quote]
