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FROM THE October 2008 ISSUE

Preventing pinholes in resin parts

RELATED TOPICS: RESIN | ENGINE
Q: I've played around with making resin engine parts for a year now. I like the results, but how do you keep from getting those pinholes in the resin parts? I toss away about 70 percent of the resin I do, because they come out with too many pinholes in them.

- Gene Davis
via E-mail


Ken: Those pesky pinholes are caused by air bubbles that get trapped while you're mixing the resin.

Be sure to slowly mix the two parts in such a way as to minimize the amount of air that's pulled down into the mix. That might not be possible with some of the quicker-setting resins, which almost force us to stir fast. If that might be an issue, try a slower-setting resin.

No matter how hard we try, though, some bubbles will likely get swirled into the mix.

One way to counteract that, at least in a one-piece mold, is to pour a small amount of resin into the cavity, work it into all the nooks and crannies with a small brush, and visually examine it for air bubbles. Then slowly pour the rest of the resin mix to fill up the mold. Here again, slow resin will work better.

If you're using a two-piece mold, and you don't have access to the inside during the pour, be sure you have enough airways to allow air to escape from the mold while the resin is entering through another channel.

One trick I use is to lay the mold on a piece of plywood and hit underneath the wood with an orbital sander. The vibration helps to loosen bubbles that might stuck to the side of the mold.

We also could mention vacuum machines to pull the air bubbles out of the mix, but that's a subject for another time, in an article that would take up more space than we have here. We hope we've shed some light on both your questions, Gene. Good luck!



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