Making a male mold for vac canopy

[jefferysl]

I'm trying to make a replacement canopy for an old yellowed vac canopy. What I want to do is fill the old canopy with a compound that will harden without bonding with the "master". I can then separate the old canopy from the casting and use the casting as a male mold to either smash form or vacuform a new canopy. What should I use for making the casting? I'm thinking plaster of Paris but am unsure if it is strong enough.

[tberres2]

I would recommend Milliput rather than plaster. You should put mold release on the canopy interior and be careful not to distort the shape when you fill with Milliput. The great thing about Milliput is that it won't heat up or shrink as it cures. Also, it is extremely easy to sand, carve, and shape.

[jefferysl]

tberres2;

Thanks for the reply. I have Milliput black...what would you use for the mold release agent?

[chukw]

I made my Me410 male mold with plaster- really strong and it came out nice and smooth. I soaked it with thin CYA glue to give it a "shell". I used silicon mold release agent from an abortive resin casting attempt- you could try Rain-X glass protectant. It's a nice silicon lube that lets water roll off your windscreen, so it may well work on molds! I've used it to keep paint from clogging the needle of my airbrush.

HTH_ and cheers!

chuk

[JackMan]

tberres2;

.what would you use for the mold release agent?

I'd heard some folks have had success Vaseline.

Chuk, I've heard plaster of paris doesn't stick to vacform or plastic canopies (tho' I've never tried that myself). Any feedback on that? If it's true then I suppose no release agent is needed.

[Snowbird3a]

I'd heard some folks have had success Vaseline.

Chuk, I've heard plaster of paris doesn't stick to vacform or plastic canopies (tho' I've never tried that myself). Any feedback on that? If it's true then I suppose no release agent is needed.

When I made a Plaster-of-Paris mold of a Falcon Vac canopy, I didn't use any mold release, and it worked great.

I made a female mold of the canopy and made it the right size to fit in the rectangle well of my Mattel unit. Drilled holes in places to draw down the clear plastic sheet, and had a quite bit of success.

Good luck, Tony

[jefferysl]

Thanks for the replies. I decided to go with plaster of paris with a hardener I found at Hobby Lobby. I intend to use copper foil for canopy framing. I've got Rain-X, so thanx, chukw. By the way, did you get the wheel well problem solved on the 410?

Scott

[JackMan]

When I made a Plaster-of-Paris mold of a Falcon Vac canopy, I didn't use any mold release, and it worked great.

I made a female mold of the canopy and made it the right size to fit in the rectangle well of my Mattel unit. Drilled holes in places to draw down the clear plastic sheet, and had a quite bit of success.

Good luck, Tony

Thanks Tony. And good tip about drilling holes. Where are the best places to drill these holes? At the base? A picture would be good.

[jefferysl]

Well, I'm having very good success. I stopped by Hobby Lobby and picked up PermaStone, Seal-In (adds strength), and AIRID (mold release for plaster castings). Results are fantastic. The castings are very hard, smooth as glass, and sandable. I am now investigating how to do the framing. My current idea is to draw the frames on the canopy with a pencil, then cement strips of copper foil to the casting. To add strength to the adhesion of the frames to the casting, I'll coat it with Future and then prime it. I'll try to post pictures, not sure if this will work....

[JackMan]

Wow, Jeffery! That looks great!

My current idea is to draw the frames on the canopy with a pencil, then cement strips of copper foil to the casting

Not sure if this works, but how about also trying thin strips of electrical tape or even Tamiya tape?

Btw, what are you using for the vacuforming? Mattel Vac-u-form?

Edited January 18, 2012 by JackMan

[jefferysl]

Jack-man;

I'm cementing the strips to the casting with cyanoacrylate glue, then I coat the casting with future. I then spray on a coat of gray primer. This reveals any bumps,etc. I sand the bumps, give another coat of primer, and finish it off with a final coat of future to give it a glossy finish. I'm hoping that this will be robust enough to do several vacuform canopies, as you always have several that don't turn out good enough. I use a pretty crude vacuform technique that is home made, yet I've had really good results over the years. I made a box out of aluminum sheet, drilled holes in the top and a big hole in the side. I hook this gadget up to the vacuum cleaner accessory hose. I then take my male mold and mount it to a lump of blue tac, being sure to eliminate any overhangs that will make it tough to extricate the master from the plastic after I vacuform the canopy or whatever. I then tape (yes, tape) a sheet of plastic to a bent coat hanger, turn on the vacuum cleaner, and heat the plastic over a lit sterno can. When the plastic begins to sag, I plop it over the male mold and immediately shut off the vacuum cleaner. Sounds goofy, but it works really well! Anyway, the casting in the picture is the nose canopy for a Sanger KI-21 Sally. It's a pretty nice kit (for a vacuform) let down by absolutely rotten clear parts. I'll let you know how it works out.

Scott

[Tailspin Turtle]

Adding frames to the master looks like a lot of work, considering that the frame thickness isn't much more than the thickness of a couple of coats of paint (interior and exterior color) at our scale on prop planes, certainly not on a jet. Plus with a male mold, it's hard to get a sharp definition of the edge of the frame. I prefer to vacuform over a smooth mold and then apply narrow strips of thick masking tape to the canopy to represent where the frames are while masking it. When the masking is complete, I then carefully pull off the tape representing the frame. A little repair of the mask is sometimes necessary and a coat of Future also helps to seal the edges of the masking. This is an example: a 1/72 scale canopy for an AJ Savage.

[jefferysl]

Tailspin:

Sounds like a flexible technique that is easier than what I'm doing. I was shooting for an effect that you'd get like a Squadron or Falcon canopy. As you can imagine, doing curved frames is difficult using my planned method. Then there is the durability question...what happens when a frame falls off the master during rough handling? Using your method, I would only have to sand the inaccurate framing off the casting and vacuform. Well, I have a number of vacs to try out different techniques on, thanks for the input.