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Sep 16, 2002, 07:06 AM
ParkScaleModels
zbrubaker's Avatar

Plugs for vacuum forming


Can anyone out there give some insight as to the best material for making plugs for vacuum-forming? I plan to vacuum parts in both styrene and Depron.

Would MDF (medium density fiberboard) work for making a plug? Would it be necessary to fiberglass it?
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Sep 16, 2002, 09:17 AM
Team 30 Micro EDF
Mike Taylor's Avatar
The plugs need to be smooth if you want the final product to be smooth as well. For making male plugs, soft pine carves easily, even hard balsa is good. Fill and finish with resin for a super-smooth finish with no grain for the parts to stick to. Some people prefer unfinished wood, sanded smooth. I've had wheel pants and cowling formed like this at a local magnetic sign shop.
Some difficult parts like landing gear leg fairings can be carved for two pieces of wood tacked together, then unfolded over a shallow inverted 'V' of wood to form the mold. After molding, you refold along the leading edge...
Sep 16, 2002, 05:40 PM
Dr John
pmpjohn's Avatar
The best wood for pattern making is mahogany. Pricy but the best. Carves easily and sands smooth. Sealing and a glass smooth surface is not recommended unless it is a female mold where the show surface will contact the mold or a clear canopy where both surfaces are visible. A slightly scratched surface (320 grit) with allow better air evacuation and still not print through to the show side of the plastic. The hot plastic is more likely to stick to a resined surface than to raw wood.
Sep 16, 2002, 08:16 PM
EB-66C Team Member
J Morgan's Avatar
I have a small vac-form that I use for canopies, wingtips, fairings, etc. Longest piece I can vac form is about 7". I use only blue foam for molds. Carves to shape in minutes, sands like butter and then a coat of vaseline for a release agent. I have no problems but I normally use .010 or .015 plastic. Parts come out great with no damage to the mold. You could try it, shouldn't take but 30 minutes to find out if it works for you.
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Sep 17, 2002, 07:04 AM
ParkScaleModels
zbrubaker's Avatar
I'm looking for a material that is durable and I can use at least 100 times. I don't think foam would work too work for that.
Sep 17, 2002, 02:08 PM
It's just PLANE silly!
balsaman's Avatar
I use bare pine.

Eric

www.e-zflight.com
Sep 17, 2002, 06:40 PM
Dr John
pmpjohn's Avatar
The pine or the mahogany will probably give you the 100 pulls if you are pulling thin (.030 or less) plastic and don't overheat the plug. Our production tooling is cast with an aluminium powder filled hi-temp resin but we pull up to .125 plastic and may run all day long as fast as as we can change out the plastic.

Eric, Try the mahogany one time and you will never want to go back to pine.
Sep 17, 2002, 11:24 PM
It's just PLANE silly!
balsaman's Avatar
I will. Next plug I make. Thanks.

Eric

www.e-zflight.com
Sep 18, 2002, 09:00 AM
ParkScaleModels
zbrubaker's Avatar
pmpjohn-

I'm planing on using mostly .030 styrene and .09 depron.

I also have some existing parts (made of styrene) that I want to duplicate. Are there any materials/methods you can suggest to do this?

It would be great if there was something I could pour into the existing part, that woulden't stick to it, but would be hard enough to use as a plug.
Sep 18, 2002, 09:44 AM
Team 30 Micro EDF
Mike Taylor's Avatar
Plaster of Paris comes to mind...
Sep 18, 2002, 11:19 AM
It's just PLANE silly!
balsaman's Avatar
Use plaster of paris. Leave the existing styrene part on the plaster. I am pretty sure this will work, altho I have not tried it. The new part will be a little bigger by the thickness of the styrene your pulling.

Eric

www.e-zflight.com
Sep 18, 2002, 01:38 PM
Flying Welder Pilot
Plane Crazy's Avatar
Plaster of paris will work fine. Although can be a little brittle on dramatic pulls. Usually you can get 20 to 50 parts off of them before things like sharp edges start to deteriorate. You can also add strands of hemp or strands of glass cloth to the mix to strengthen to part.

You can coat your plastic parts with Crisco for a mold release and pour the plaster into them to create plugs. Make sure you dry the plaster for a week or so on a concrete floor to suck all the moisture out of them before you pull parts.

Also you can create plaster molds from plaster parts by sealing the plaster with shellac, let dry and then coat with Crisco and pour plaster over the part.

Picture below shows a plug pattern on top, a plaster female mold, and then a plaster male tool for vacuforming Space Walker wing tips.

This does make a good mess in the garage.

Gordon
Sep 18, 2002, 04:45 PM
Dr John
pmpjohn's Avatar
Plaster of Paris and Crisco will work. I prefer Hydrocal and spray Pam myself. Wipe out most of the Pam or several coats of paste wax will release the plaster. Hydrocal can be found in the model railroad dept. of a good hobby shop in small quantities or in hundred lb. bags at a builders supply. In a humid climate it has a limited shelf life.
I have not pulled over styrene but would suspect limited tool life and possible sticking. The only release agent we ever use for the actual vac forming and only on a troublesome mold is a little baby powder dusted on and mostly wiped back off.

John


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