Touching Pee-pees in the Dark and Adventures in Airplane Bonding

Our first really big pane is about to come off of the line. I guess it is easy to see that I was slacking. Not really, just got side-lined by a bunch of stuff.

Today, I wanted to talk about the bonding experiences. We are pretty good with the cheap and cheerful 60min and 90min epoxies available from Loctite. In general, they are worthy of their cost. For the most part:

•  they get it done
•  are easy to clean
• decent finish that is sandable, but micro-balloons help immensely
• and wet chemistry does not rip the skin off of your hands

 The other side of the coin is that :

• they are not super hard
•  sometimes leave a sticky surface which needs hand washing a bunch of times to get the surface clean
• cheap means heavy
• in the warm, humid air of Florida sometimes the pot runs really fast.

It is exciting to see it melt through two cups and run epoxy all over your surface and drip down your leg. The steam is cute on a  100% humidity afternoon. Around here, it is not uncommon to see rising off of your sneakers, but it is exciting to see rising off of your freshly-laid skin. It still burns your skin ... boiling water is hot... If the cup gets to be hot to the touch, or the epoxy runs really fast then you only have a few more minutes before the epoxy fixes.

We have some other adhesives and layup chemistries used by the "pros". Ok, yikes. There are enough flames, warning symbols and ventilation requirements that we honesty did not have the facilities to use them. However, some basic tests show that the stuff from Aircraft Spruce is really hard and easy to sand. It stuck to everything , was hard to get off of skin, and 10:4 is not an easy ratio to eyeball. So it needs a scale and  a fan to pull air away. I can only say it must be best with vacuum-bagged molds and infusion systems.

I would suggest using either, just know what you are getting into. With any bonding system, rough your bond area with steel wool, clean your area with a clean cloth and alcohol. Cleaning with alcohol is to pick up any grease, dust, grime and hair. Test your bond between scrap pieces of material.

Adventures in Composites: Two Bogans and the Art of the Lay... Up

After a year of sitting, our polyester resin had spoiled. So we contacted some people and they said you could do it with just about any medium cure time epoxy. Out into the proper disposal container for petro-chemical waste. Yeah, I went there. Off to the local hardware shop for some epoxy. We bought several batches of 60 min epoxy. Some of the information that our friends told us suggested that we could use isopropyl alcohol to help keep the viscosity of the epoxy down as it is laid up.

Information like this is when it gets exciting. We found out a few things. You can paint the alcohol onto a layer to help flow the epoxy and to reduce the bubbles and flatten wrinkles. I would suggest that pour some alcohol into a cup and paint it on where you need it. Each layup will be different so it is hard to say where you would have issues.

There were some bubble generators in the seam where the semi-mold met the backing. This is probably pretty obvious, but it was due to training air under the resin laden cloth. Our mold also had several regions with nearly perpendicular sections which were hard to wet. In areas like that, I would suggest liberally pre-painting. Be careful not to pool the resin in the bottom since that is not where you want the part to be strong. Another observation was to make sure that when each layer is put down, both people should work in the same direction. Do not work the resin from the nose and the tail. It makes wrinkles and other defects.

It is very important to make sure that each layer has as much of the resin out, or at least even distributed as possible. This means that all of the bubbles, wrinkles and puddles need to be worked toward the edge of the layup. A roller and brushes are the weapons of choice for this work. The handle edges are great for wringing out excess resin from tight radii.