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Making a glass cowl from the inside of a plastic one ?

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Old 09-11-2012, 11:00 AM
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TampaRC
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Default Making a glass cowl from the inside of a plastic one ?

I have an abs cowl and want to create fiberglass copies using the inside of the abs one as a mold. Has anyone tried this and what would you use as a release agent?
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Old 09-11-2012, 11:35 AM
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Default RE: Making a glass cowl from the inside of a plastic one ?

Wax AND PVA would be the most reliable release.  You should test the release on a scrap of ABS first. 
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Old 09-11-2012, 11:38 AM
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Default RE: Making a glass cowl from the inside of a plastic one ?

Whats PVA ?
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Old 09-11-2012, 11:54 AM
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Default RE: Making a glass cowl from the inside of a plastic one ?

PVA stands for polyvinyl alcohol. It's primary job is to create a barrier that prevents any chemical reactivity between the release surface and the layup resin.

I like to use Part-all Paste #2 release wax and Part-all Film #10 (PVA). I've never tried to release off of ABS so I'm giving you the safest release combination. Wax alone may work but I think you might run into problems depending on your chosen resin. You should test your chosen combination on a scrap first.
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Old 09-11-2012, 03:16 PM
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Default RE: Making a glass cowl from the inside of a plastic one ?


Quote:
ORIGINAL: TampaRC

I have an abs cowl and want to create fiberglass copies using the inside of the abs one as a mold. Has anyone tried this and what would you use as a release agent?

Using the inside of the ABS cowl as a mold will result in a slightly smaller size finished part. Make your mold using the outside of the ABS for the mold and your parts will end up the exact same size as the mold.

Regards,

Dennis
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Old 09-11-2012, 03:19 PM
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Default RE: Making a glass cowl from the inside of a plastic one ?

I was thinking about that option too
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Old 09-11-2012, 03:36 PM
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Default RE: Making a glass cowl from the inside of a plastic one ?

I havebeen doing this for years Partall wax and PVA does the job just fine. the size reduction is a non issue. You will loose approx 1/16".
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Old 09-11-2012, 07:24 PM
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Default RE: Making a glass cowl from the inside of a plastic one ?

Ditto on Speedy's comments!

I have also done this for years. It is much easier than having to make a female mold, first . . . saving a lot of extra time and effort. The loss in thickness is negligible. Just take care of it with a quality wax and PVA as described several times now, and you should be just fine. Realize that as a "mold", the plastic is not nearly as durable as a thick fiberglass mold. It is thinner and more brittle, so it won't last forever. But you should get several copies before you start having issues with the plastic cracking, splitting, etc. If you only need a couple copies, this is a fairly ideal method, all things considered.

But, If you later find this is a favorite plane, and you're making a lot more, save one of your more perfect lay-ups as a new master. Then you always have something you can use to make a female mold later, if needed.
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Old 09-11-2012, 10:38 PM
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Default RE: Making a glass cowl from the inside of a plastic one ?

exxxxleclent!!!!!
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Old 09-12-2012, 05:19 PM
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Default RE: Making a glass cowl from the inside of a plastic one ?

Im making a mold to mold a cowl for my Dewey. The one it came with is too short for the 4 stroke, and it was cut up for the original motor. So I made a base plug from styro foam, and covering it with Bondo. When I get it to the shape I need, then will give it a coating of resin, polish it and make the final mold.   I wish I could do what you are doing, it would have been done by now!
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Old 09-12-2012, 05:38 PM
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Default RE: Making a glass cowl from the inside of a plastic one ?


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ORIGINAL: acdii

Im making a mold to mold a cowl for my Dewey. The one it came with is too short for the 4 stroke, and it was cut up for the original motor. So I made a base plug from styro foam, and covering it with Bondo. When I get it to the shape I need, then will give it a coating of resin, polish it and make the final mold. I wish I could do what you are doing, it would have been done by now!

The bondo will dissolve the foam. You need to fiberglass the foam plug with epoxy resin. If it's just a one off, you can simply dissolve the foam away with laquer thinner after you have glassed it. What you have left is a fiberglass cowl.

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Old 09-12-2012, 06:36 PM
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Default RE: Making a glass cowl from the inside of a plastic one ?

Since we are still talking,  what about integrating carbon fiber cloth with the fiberglass for additional strength?
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Old 09-13-2012, 04:41 AM
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Default RE: Making a glass cowl from the inside of a plastic one ?

So I noticed, but the shell is coming along OK. About 2 more layers are needed before I can put the final shape on and give it a coat of resin for a smooth finish. I have about 3/16" build up of the plastic filler now in a rough shape.   This is my first attempt at making something like this, and experimenting with leftover body filler seems to be working.
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Old 09-29-2012, 11:39 PM
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Default RE: Making a glass cowl from the inside of a plastic one ?


Quote:
ORIGINAL: TampaRC

Since we are still talking, what aboutintegrating carbon fiber cloth with the fiberglass for additional strength?
Tampa,

You could, but I doubt you need that much strength that it is worth the relative difficulties or the extra weight. By using fiberglass, you already have a far superior strength and durability in your cowl than the original plastic one. For .40 - .60 sized planes, I usually lay up my cowls using two layers of 3.5 or 4 oz FG cloth cut into strips with some overlap. I will run about a 3/4 - 1 inch strip around the rear (or trailing edge) of the cowl for extra rigidity and for durability if I plan on drilling holes at that location for mounting screws. Strength and ease of layup also depend a lot on the shape of the cowl. Long, flat sides will flex more and are weaker than those with corners, arches, corrugations, etc.; but these are the shapes that make getting the cloth to lay down more difficult.

It also largely depends on the type of CF cloth you intend to use. Some types are very rigid and do not conform to compound curves well during simple hand lay-ups. Using an existing plastic cowl doesn't sound as if you would be able to put your lay-up under any significant pressure (such as vacuum bagging) to ensure the CF cloth lays perfectly.

If you want a little more strength, for a very minimum weight penalty, and want to keep this relatively easy, you might consider using 1/4" (or similar) carbon fiber tow in an overlapping weave pattern. I tried this on the nose sections of some of my latest warbird racer fuse molds and was happy with the results. A couple of pictures demonstrating how I incorporated this method in my last 1/10th scale (.40 sized) P-47 hand layup are attached below.
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Old 10-01-2012, 04:54 AM
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Default RE: Making a glass cowl from the inside of a plastic one ?

If you want the parts to be really slick then paint the inside of your ABS parts first. Some primer with a light sanding followed by color. Wax and polish a few times and then spray or wipe (depends on which you use) PVA into the 'mold'. Spray some primer into 'mold' let dry then do your lay-up.
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