We have a Cowl Mold; Inspired by Sid

The last few days, when I have been looking at the rear cowl, I have thought that the trailing edge shape reminded me of something, but I couldn’t figure out what. Turns out, it is the character Sid from the cartoon movie, Ice Age. While I am fairly certain this destines Brian’s Defiant to henceforth be named Sid, I couldn’t help but share my revelation. It gave me a pretty good chuckle.

The last few days in the Garaggio have been pretty exciting. Since Jodi’s working visit, I did add one more tooling flange just forward of the cowl to firewall intersection. On the first version of the cowl, it was challenging getting the plies of glass to end reasonably well and have the bag sealing tacky tape all in a 2″ area. The 4″ wide flange will be great to separate the plies of cloth and bagging materials and give more room to work. It will also make the mold dimensionally stable.

From there, on Wednesday and Thursday morning it was all the usual steps to ensure the mold releases from the plug. I rubbed it down with 5 coats of Part All mold release wax. I may or may not have mentioned it before, but I really hate waxing. It really isn’t that hard, and it certainly signifies that we are ready to make a major step in progress. But somehow, it always takes me way longer to do than it should, and its a lack of enthusiasm causing it. Never the less, a full 5 coats was put on the plug and tooling flanges. Spraying PVA Thursday morning was a breeze and pleasure compared to the waxing. With both done, the plug was ready for a mold layup.

This time, I was a bit smarter than last. I waited until Kevin had the time to come help. Good thing I did as this layup took a good 4 hours with the two of us. We did make things a bit easier on ourselves by using the “extra slow” hardener. I used West System Epoxy as it is cheap, I had a ton of it on hand, and it is available locally. A lot of you will ask again why not polyester, and I haven’t slowed down long enough on this project to give it a try and learn how to use it. I will eventually as I have some.

The layup schedule for the mold was:

  • 1 ply deck cloth
  • 2 plies uni/bid
  • 1 ply chopped strand mat
  • 1 ply deck cloth

Usually, I would use bid for the whole second and third plies. However, I had a ton of “scrap” uni laying around that I wanted to use up. My scrap pieces were 30 and 15 inches wide and 5 feet or so long. These pieces were folded and old, so not suitable for a flying part or anything truly structural. They worked fine, but bid is easier to work with. The bid wets out easier too.

Of course, we had some of the same issues with wetting out the chopped strand mat. It is a pain in the butt to work with, takes a lot of time to wet out with Epoxy, and is prone to air bubbles that are difficult to get out. Even so, it did build up the thickness, and knowing how thirsty it was, I could have Kevin mix up more epoxy each round than I did in the first top cowl mold.

I did make an error of omission during the layup. I forgot one of the plies of BID/UNI from the original layup schedule. So the mold ended up a bit thinner than desired. Surprisingly it is actually pretty rigid with the whole perimeter tooling flange. If this were a production mold that I was intending on pulling many parts from, I would go back and add more stiffness by adding plies. However this mold will pull just a few parts, so it will be fine as is.

Today, I released the mold from the plug. It was again surprisingly easy to do. I am so impressed with the mold release wax and PVA combination. It is a bit more labor intensive than I would like, but it sure does a great job of releasing. It took no more than 30 minutes to have the mold off.

From there I cleaned it up. That involved getting rid of stray clay and a thorough wash to get rid of the PVA. Cleaned, I then started on the path of polishing the surface. It was pretty good as it came off the plug, but I did do a round of each 400, 800, and 1000 grit sand paper on the DA. I think that should do it.

I likely will add a wooden structure around the mold for two reasons. One, it will help with a bit of rigidity since I missed a ply in the original layup schedule. The other thing is the wood structure will give me feet for the mold. Right now to put this mold on saw horses, I have to rest the mold on areas that will be a part of the final cowl. This would slightly deform the cowl shape, which is obviously not right. A wood structure will allow the shape to be unaffected. Other than that, the top cowl mold is ready to be used.

Early next week I will be prepping to make a top tool cowl out of fiberglass. I debated going right to the final carbon cowl, but there are a few advantages to making one out of fiberglass first. I should also be able to get a mold made for the lower cowl. It is significantly smaller than the top cowl, and should be simpler to make.

Some of the materials used to make the mold described in this Post:

The below images are amazon links, click on them to learn more.

Mold Release Wax

Poly Vinyl Alcohol (PVA) Mold Release Film

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