Making Canopy Plugs

[Mike Griffin]

To duplicate a certain canopy I have take the actual canopy and filled it with plaster of paris and let it dry for a few days.  It comes right out of the plastic canopy without any trouble and then duplicate canopies can be made from this plug.  My question is, is there a better material to use for this than plaster of paris?

Thanks

Mike

[50+AirYears]

In the Model Railroad section of your LHS, you might find a milk carton sized container of a Hydrocal plaster.  Supposedly takes a little longer to set up than POP, but is harder, more durable, might be slightly finer surface.

[GGeezer]

Mike,
My favorite cast plug mold material is autobody filler. Its tough and resists the heat of thermoforming. I do not like plaster because it is so hygroscopic and if you don't bake it absolutely dry, the heat of thermoforming will cause the moisture to give problems.
You can cast the body filler directly into the inside of the canopy but since the body filler is filled polyester resin, it will most likely ruin the canopy. You have to wax the canopy surface and then spray on a fairly heavy coat of Polyvinyl-alcohol barrier film. This will protect the plastic canopy and allow for plug removal. The canopies molded from this plug will be smaller than the original because of post mold shrinkage.
The best solution and the one I usually use is to make a silicone rubber mold of the outside of the canopy then cast a body filler plug in the silicone mold. No barrier film is needed. The canopies will now come out on size in most cases. Silicone casting rubber can be obtained from the Smooth-on company. http://www.smooth-on.com/

Orv.

[john e. holliday]

In my opinion, soft pine is the material of choice for heat/vacuum forming.   It is easy to carve/sand.   In fact I don't remember using any finish on the wood other than final sanding with 400 grit paper.

[Mike Griffin]

Hi Doc

What I was trying to do was take a canopy I already have, fill it with some sort of compound and when it dried pull it out of the canopy and use that as a mould for making more...

Mike

[Wynn Robins]

Moulding epoxy - just put a release coat inside the canopy first

[Larry Renger]

Once when I visited Peck Polymers, they showed me their canopy forms.  They were some sort of Metal filled epoxy.  This was for long term production, of course, but I bet they don't distort, and probably chill the hot plastic in a real hurry.

What about autobody filler mixed with chopped glass, ground walnut shells, kitty litter, sawdust or other shrinkage limiters?  Saves on the amount of putty, too! HMM, Kitty litter is "rock solid" (sorry), cheap and available.  I would recommend the fresh stuff. 

[Tim Wescott]

If the molding epoxy that Wynn mentions is the stuff that I think it is, that's what you want.

At any rate, my brother is a part-time pattern maker; he uses some moldable plastic that pours well before it's set up, is workable when it's done, and doesn't shrink appreciably.

[skyshark58]

I use "DURHAM'S WATER PUTTY" Buy it a the harware store in big cans. Cheap stronger than plaster of Paris and very smooth. Let it cure for a few days so all the moisture is gone.  Works for me

Mike Potter