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How To Make Mold For Cowl

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Old 09-30-2007, 08:18 PM
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GSAV8R
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Default How To Make Mold For Cowl

I have a fiberglass cowl for a model. The cowl is no longer available. There is another person building the same scratch built model. How can I use my cowl to make a mold so this other person can build his cowl?
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Old 09-30-2007, 10:56 PM
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Default RE: How To Make Mold For Cowl

Hello, I have a method that my good friend showed me that might be of some interest to you. I was in the same situation as you, I had a set of plans and needed a cowl and the kit was no longer in production and no after market one was available. I was lucky to finally come across a kit and I was able to use that cowl as a master. This method is quit simple and not expensive to do. It involves the use of plaster of paris. You need to mix up a large enough quantity to completely cover the outside of the cowl. However long it is is how deep you need to make it. I mixed up a bunch and used a deep plastic pail. After you have the mix ready pour some into your mold container then set the cowl right into the bottom of the mix. Not all the way down just far enough to submerge the front. Then pour the remaining mix all around the perimeter of the cowl all the way up to the end. After you pour it all in give it a few good taps on the side of the container to make sure all the plaster mix has settled nicely around the cowl. Let it sit over night and completely harden. Now is the tricky part, REMOVING the ORIGIONAL COWL!! Another little trick he showed me is to make sure you cover the outside of the cowl with some type of nonstick agent to help it release from the hardened plaster. He told me that he uses PAM!! The nonstick spray for cooking. Don't be stingy with it either, spray on a heavy coat before you place the cowl into the plaster mix. This will help it release. The best way to remove the cowl after everything has hardened is to use compressed air. 100 PSI ar more. Spray it down between the cowl and plaster and work it loose gently. Only put the plaster on the outside DON"T FILL THE INSIDE! I personally have used this method and it yeilded me a nice mold to use as a layup for the fiberglass. If there are any imperfections in the plaster after you remove the cowl you can fill them in with model filler. Make it nice and smooth just like the outside contour of your cowl and you have yourself a nice mold. As far as laying up the fiberglass you need to use a release agent such as a special wax used for fiberglassing before you lay in your fiberglass.
There is a lot of things you can find on how to make the fiberglass cowl on line. I hope that this is helpfull. Oh just one more thing, a note. The plaster mold will be HEAVY!! Not unmanagable. Mine weighs about 15LBS. Best of luck on you project.
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Nevin
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Old 10-01-2007, 08:53 PM
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Default RE: How To Make Mold For Cowl

Thank you very much for responding! This sounds like a simple way to make a mold. I will give it a try. One question, though. Will the cowl try to float out of the plaster filled container?
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Old 10-01-2007, 10:37 PM
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Default RE: How To Make Mold For Cowl

No, the plaster is quite thick. the cowl will be held tightly. make sure you hold it in position as you pour the plaster. once it is poured around the cowl it should stay in place. Let me know how it turns out.
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Old 10-02-2007, 12:45 PM
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Default RE: How To Make Mold For Cowl

A coating of Vaseline will allow the plug to come out of the plaster very easily.
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Old 10-02-2007, 12:53 PM
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Default RE: How To Make Mold For Cowl

Don't forget you want the plaster to seperate from the bucket easly, so coat the bucket also!
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Old 10-10-2007, 07:22 AM
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Default RE: How To Make Mold For Cowl

Wrong post.
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Old 10-10-2007, 07:53 AM
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Default RE: How To Make Mold For Cowl

Also....Seal the plaster mold prior to continuing on with your fiberglass lay up...

Have Fun...

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Old 10-10-2007, 08:01 AM
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Default RE: How To Make Mold For Cowl

Can one of you chime in on how to do the lay up of the fiberglass inside the mold? I can see draping fiberglass around a plug, but I'm not sure how one would put fiberglass inside a mold.
THanks
sam
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Old 10-10-2007, 11:44 AM
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Default RE: How To Make Mold For Cowl

Put a reasonably heavy layer of PVC Mold Release in side the mold.

When that has dried, spray a coat of gel coat inside the mold and let dry.

Now cut some 2oz fiberglass cloth into strips about 1 1/2" - 2" wide by about 12" (width and length will vary according to the cowl size. These measurements would be for a typical 40 or 60 size cowl ). You are going to need a bunch of them since you will want 2 layers of fiberglass cloth. Also cut strips of 4oz or 6oz fiberglass cloth (you will need enough for 1 layer for a 40/60 size cowl ).

Now mix up some 30 minute epoxy (I like to dilute mine with acetone - 10% BY VOLUME - for a longer working time )

Brush or spray a medium coat of resin over the interior of the mold..

Using the 2oz strips, lay ONE layer in the cowl. Overlap each strip by 1/2". Use a flux brush, and brush a coat of resin over the glass cloth. You need to make sure that the resin completely penetrates the cloth (white spots indicate the resin didn't penetrate completely ).

Once this is completed, do the second layer of 2oz cloth the same way.

Finally, add the 4oz layer(s) of cloth and let everything dry (typically 24 - 48 hours depending on temperature).

When you remove the cowl from the mold it will be flexible. Do any minor final shaping as needed and set to one side for about a week to harden up.

Now you can use soap and water to wash the mold release off the cowl. Any holes/pits/etc fill with spot putty (auto section Wal-Mart ) and sand as needed.

Now you can cut the front of the cowl out.

Wipe the cowl down TWICE using ALCOHOL and clean cloths and prime.

Now you can fit the cowl and make any additional holes, etc, prime (again), wet sand, and paint.
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Old 10-10-2007, 12:21 PM
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Default RE: How To Make Mold For Cowl

Good instructions. One way I have used very successfully is to lay the strips out on cardboard or other stuff throwaway item and wet them with a small paint roller, then lay them in and tuck them down with the brush. Push the first ones in real tight our you may have some bondo-ing to do. This way you are sure the glass is wetted thru!
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Old 10-10-2007, 11:08 PM
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Default RE: How To Make Mold For Cowl

Thanks very much for the great information!
Sam
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Old 10-14-2007, 10:21 PM
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Default RE: How To Make Mold For Cowl

Excuse my ignorance. I have never done any fiberglassing but am curious why the plaster of paris would not be poured inside of the cowl that is to be duplicated that had been coated with PAM or form release or vaseline? That way the fiberglass cloth would be laid over the outside of the form. The cowls I need to make fit over the nacelle so the inside dimension would be more critical.

Again this question comes from a noobie that has never done any fiberglassing but needs to make a pair of longer cowls for my Bud Noseen Cessna 310 that I installed a pair of Quadras on (so the original cowls are too short to cover the Quadras).

Thank you.
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Old 10-14-2007, 11:31 PM
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Default RE: How To Make Mold For Cowl


Hello, I am the person who answered the question first. I would not recommend using your cowl as a mold to fill with the plaster because I would be very leary of being able to remove the plaster from the cowl. The plaster is very heavy and brittle after it has completely set. I would be afraid of ruining the origional cowl trying to get the plaster out. If you do want to try it get yourself use a cowl that you don't mind using as a test mold. If it were to get ruined it wouldn't be a big deal. Try to coat it as you would the outside for my molding process using the recommendations listed by me and others, and fill it with the plaster. After it has dryed see if you can get it to release from the cowl using air pressure. Using the cowl as a master the way I explained it allows the air to free the cowling up off the plaster. With it used the way you want I do not see how the air will be able to break the bead and release the cowl. Like I said it is worth a try. I have used the method you have asked about to make master molds of canopies. It works well because the plastic canopy releases easily from the plaster and the mold has excellent detail. That makes for an excellent male mold for use in for vacuum forming. If you do try it please write back on this forum and let me know how successfull it was.
Regards
Nevin
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Old 11-16-2007, 12:50 PM
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Default RE: How To Make Mold For Cowl

What if the cowl already has holes cut for the engine head/exhaust or is a two-part cowl? Is it still possible to pull a mold from it?
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Old 11-16-2007, 02:23 PM
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Default RE: How To Make Mold For Cowl

You can use modeling clay to make any repairs or fill holes, or even add features that were no there before.
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Old 12-01-2007, 09:41 AM
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Default RE: How To Make Mold For Cowl

Hey check out fibretech gb's website theres a step by step tutorial on there including photos on how to make a cowl from an existing part.

Hope this helps
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Old 12-25-2007, 08:27 PM
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Default RE: How To Make Mold For Cowl

what is the url of this website?
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Old 01-20-2008, 07:12 PM
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Default RE: How To Make Mold For Cowl

A couple of places to look for cowl making tips;

RCU Composite Forum;

Fiberglass How to: Plug to Mold to Parts by DocJones199

How To Make Mold For Cowl by GSAV8R

Other places;

CST http://www.cstsales.com/index.html Look in the Tutorials (top bar) for different tutorials in PDF format.

Steve Jones www.fiberglassmoldmanual.com sells a comprehensive manual about making molds, parts, making plugs, multiple piece molds for complex parts and more. Lots of good info in the manuals.

Fibretech Great Britain http://www.fibretechgb.co.uk/DefaultHome.htm has a tutorial for making a glass cowl from an ABS cowl under Working Tips.

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