Making a copy of a cowling

13 posts in this topic

Posted

Hi all,  I'm trying to make a mold for/from a cowling I just picked up.  I did try some of that blue heat shrink plastic that they cover boats with.  It's not perfect by any means, kind of have it on the top half, but it doesn't want to fit the bottom without hugh wrinkles that I don't think will come out when I shrink it.  My thinking was the plastic would keep the new fiberglass from sticking to the original cowl.  Wondering if anyone has tried covering a cowl with mold release and then making a mold that way.  I'm scared of not being able to get the mold off the cowl once it's done, and have then ruined the cowl I just got.  JImChuk

smooth cowl 1.jpg

smooth cowl 2.jpg

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Posted


I usually just use a few coats of auto wax never had anything ever stick hard but I'm not an expert.

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Posted

Jim,

Auto wax will work on smallish parts, on a big part like the cowlings, I’d use mold release which is polyvinyl alcohol (I think) and works wonderfully.  It’s priced right also.  Good luck 

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Posted

What resin are you planning to use Jim?  That will dictate which mold release you will need to use but with the proper mold release you will not have sticking problems  use 3 or more coats of release for best results has been my experience.

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Posted

Thanks for the replies guys, I am using the polyester resin.  JImChuk

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Posted

For polyester I would wax the cowl with Johnson's paste floor wax three coats dried and buffed between coats and then 3 coats of PVA.  Good luck with your project.

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Posted

Thanks Paul,  I ordered  a quart of the PVA this morning.  Will see how it goes....  JImChuk

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Posted

Hi Jim, my two cents worth, if it’s worth that much. With the separation procedures suggested above a little air squirted between the two should pop them apart easily. Also if only one copy is needed using the cowl as a plug would work for me. I used one layer of carbon fiber then a layer of fiberglass and finally another layer of carbon, using pealply (scap pices of fabric) wetted and scrapped excess off,

makes it fairly easy to finish.

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Posted

For polyester I would wax the cowl with Johnson's paste floor wax three coats dried and buffed between coats and then 3 coats of PVA.  Good luck with your project.

I’ve made many molds and castings using these two releases.  When you spray on the PVA, mist on the first coat and the successive coats should be light.   If it beads up, you sprayed too much.  Wash it off with water, let it dry and spray again.  

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Posted

Thanks again guys for the additional info.  I'm waiting on the stuff I have on order, so I have plenty of time to collect info before I start mixing resin.  Keep it coming:)  JImChuk

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Posted

Too late last night, sleepy, plus a little of the “Biden syndrome “ to explain to the new builder, of course making a cowl on a ‘plug’ it will be oversize and may require some modifications. Will not work to replace one half of the cowl. One more thing, you can put a piece of 1/4 dowel in the camloc holes smoothed off flush, if the holes are worn oblong or misaligned I flare out both sides and fill in with cabonfibre thread and epoxy prior to  the process, then drill the dowel out later. 

Hope this might help some one Jim, not necessarily the “Master Builder”

 

 

 

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Posted

With the shape of that cowl, I think I'd rather make a mold from the inside rather than the outside.  Doing layups on the inside of the mold will be challenging, and removing the mold, unless you plan a one-off and destroy the mold, would be easier.  Plus, the inside dimension to mate with the lower cowl is more likely to be correct.

Pour foam is decent for a one-off mold.  For long term use, not so much since it continues to cure and expand for quite a while after the initial 'cure'.  Use thin plastic, like really cheap paint drop clothes, inside the cowling, pour the foam in.  Let it cure, then it looks like you should be able to slide the old cowl off by pulling the mold back toward the 'cockpit'.  Tape up the mold with packing tape (although that shrink looks pretty good to), put some mold release on that, then lay up the new cowl over it.  Just don't wait too long before using the mold, as mentioned, pour foam continues to cure and expand over time.

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Posted

Good info.  Thanks for the question and answers.

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