GW-inactive

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I have a vacuum formed clear plastic canopy. 5" wide 17" long. Pattern plane canopy.
I want to make a mold of it for making some fiberglass canopies.
Do i need to put a painted finish on the clear plastic then wax, or can I get by waxing,pva, and molding around the clear canopy bare.
The canopy has flanges on all four sides, so it will be fairly easy to mold , just don't want to put alot of unnecessary work into the clear plug if its not needed.

Thanks

Ed Smith

The quickest and cheapest way to make a mold from an existing canopy is to fix the flange to a flat surface. build a box deeper than the canopy and then pour plaster of paris into the box.

The plaster will harden in about two hours but will take a week or more for the moisture to completely dry out.. The mold surface will reproduce exactly the detail on the canopy. The inside of the mold will have to be sealed with shellac or a gloss paint. This mold will hold up for several parts before chipping around the edges.

Advantages:- Cheap, very little time involved to produce, no preparation of the outside of the canopy is required.

Disadvantages:- Limited life span. It is kind of like storing a house brick, if you drop it-Goodbye!

I used to fill the inside of canopies witth PoP. I then had a plug for further vacuum forming.

Ed S

GW-inactive

My Feedback: (4)

I figured Plaster would be full of pin holes when the mold dries. Its an idea I will think about though. Much appreciated

I will probably only need maybe 4-5 canopies from the mold.

If the PoP mold is not full of pinholes in the mold, I would suspect you could use some wax and PVA and be ready to mold . But you feel the canopy mold will need to be coated with a hard surface like paint or shellac, You know more than I do, so if you say thats the way to do it, then I guess it needs it.

Will the clear canopy pop clear of the PoP mold and be reusable?
That would make the PoP mold more considerable an option , as when the mold breaks, just make another quicky.

Still looking for advise as well about the need to finish the clear canopy with paint befor molding glass mold ? IF its not neccesary, then I dont want to do it. I could have already had the thing painted by now couldn't I? Oh well, its too dang hot in the shop. Yea,,, thats a good excuse.

Thanks for the info Ed. I will et you know if I try it.

Mike James

My first canopy plug (used to create a female mold) many years ago, was actually made from "Sacrete" (spelling?), which is "mix 'n' pour concrete. I was broke, and that's what was available.

As weird as it sounds, it made a great plug, and I was able to then make a pretty reasonable mold from it. Plaster of Paris is a much better choice, of course.

Just make sure you don't deform the canopy, by pouring "whatever" into it, and be careful with damage in general, so if you don't like your results, you can try something else.

Ed Smith

You will not get pinholes.

You will need to seal the surface, a couple of coats of clear Varathane worked good for me.

The original canopy will not be marked at all.

If you still want to make a glass mold then the canopy will not need painting. Several coats of mold release wax will suffice. Still fix the flange to a base to prevent the canopy from distorting while laying on the cloth. Do not use polyester resin it does attack some plastic, epoxy will not.

The canopy will probably have a dull finish if used as a plug in this way. If you still wish to use it sand it with at least 600 grit wet and spray on a coat of clear, the original finish will restored. Best to do this after fitting to the model.

Ed S

GW-inactive

My Feedback: (4)

Ed said :"You will need to seal the surface, a couple of coats of clear Varathane worked good for me".


Sprayed on? Low pressure? Any substitutes for Varathane if its not available?


Im off to find some Plaster today at the local depot, hope they carry it. There is also a Lowes nearby, they may stock as well.

KrisG

I am using a special plaster for jobs like this. It is called modeling plaster, and it has a finer grain than ordinary plaster of Paris. It is also more expensive. The first layer I use this special plaster, then I put ordinary ( cheaper) plaster over it to have a thicker-walled mold ( stronger).

This modeling plaster will give a very nice surface, and can shine like a mirror, if the original part from which you make the mold shines well. Ordinary POP will not give this nice surface.

If you can't find in in a Home Depot, maybe it can be found in an arts shop? The carton in which it comes shows smaller statues and things like that.

I just wax the plaster mold surface a couple of times, no painting, and never had a part stuck in the molds so far. Wax everything, and use plenty of wax!

Best regards,

Kris

Jeff Wohlt

I think the name is Hydracal or Hydrox or something like that. Most hobby shops that deal with trains seem to have it. It is much better. I also read that if you make a lather of Murphys Oil soap and lather the POP up good and let it sit and then wipe it off and do it a couple more times that it works very well. It is also washed off easily with soap and water when you pull your part so it is ready to paint.

Hairspray is also another good release Mega Hold #4 You can spray several coats and it will fill any small pin voids and then is also water soluable.

goony

polyester should be OK in my oppinion
give it 6 coats of release wax on the outside then 2 coats of GELCOAT leaving each one to go off the then apply a total of 6oz of CSM glass 2 oz first let that go off then lay up the next 4 oz you then have a perfect mould that will last a life time as long as you look after it,as long as the canopy is in good condition before you start then the mould shouldnt need any work, just wax it 6 times and gell it up and add the glass to the required weight/thickness

regards goony

GW-inactive

My Feedback: (4)

Ok! Mold is cured .
Its Plaster of Paris. Several very/very small pinholes. Like pinhead or less in size.
Studying on how to slick it off .

I'm thinking.

1. PPG Primer/Black PPG paint on mold surface ? Do not know how plaster will take this finish.

2. Several,several coats of SC Jonhsons wax? I think this will work best.

3. Aerosol spray of a clear coating of urethane? Do not know how this would react to the future glassing of parts.

4. A small amount of Spackle mixed liquid as water(runny) and take to the mold by spreading with fingers, then wiping mold clean. than wax. May work.

Anyone else want to give advise on what you have seen work before I make a decision that may ruin this mold ? (I surely hope I don't ruin it

Mike James

I've made fiberglass canopies and molds for years, but this is the first year I've made plugs intended for vacuum forming a clear part.

Beware of the final surface coat if you intend to make clear parts. I don't mean the "texture".... That obviously has to be good. What I mean is that many finishes, PPG paint included, will outgas under the heat and pressure of vacuum forming, and will not make good quality clear parts.

Lacquer-based primer is what I've heard suggested, more than anything else.

How about posting some photos of your work, so we can all have a look? There's always something new to learn.

Good luck.

Ed Smith

Do not use this. Use ONLY a recognized mold release wax after the mold is sealed. I have already stated how to seal it. You wanted a cheap, quick mold to enable you to produce 4 or 5 parts. If the finished part is not perfect it does not matter. I trust it will have to be sanded, primed and painted anyway.

Stay away from polyester resin. That material should not be in the house.


Did I miss something?

I thought he had a female mold from which glass canopy shapes were to be produced. It will not be possible to vacuum form into a female mold without drilling a number of minute air release holes. Good luck if that is the intention.

Ed S

Mike James

You're right Ed, about vacuum forming into a female mold, of course. (although you could vacuum bag some glass in there)

I think that some of us (I was one) may have been thinking of additional possible steps, and confused someone. You could:

1. Make a plaster female mold as Ed suggested, and depending on whether you poured the plaster over the top, or inverted the canopy and poured the plaster into the "bottom", you'd end up with a female mold or a male plug.

or...

2. You could, (even more steps) make female molds, then pour plaster into them, to make a male plug. (I've recently actually had to go through something similar.)

Have I mentioned that I hate sanding?

GW-inactive

My Feedback: (4)

Whar Ii have is a plaster mold over the clear canopy and base.
I have removed the clear canopy leaving a nice female mold cavity.
I want to make 5 parts. Thats all. The mold has several very small holes. like the head of a pin small.

Ed, I did read your advise, and I think I may go that route.
I will look into Varathane. Is their another brand name for that product? It looks to maybe be a polyurathane product. I looked at Lowes, and did not find Varathane. They had Clear polyurathane by Minwax and American Standard poly as well.

Will I spray an application of this or is it a brush on application?

I will continue to let the mold dry till I accumulate the needed items.

I thought the use of Johnsons paste wax and hair spray release agent was acceptable. I have used it on cheek cowl molds with great success. I guess I was lucky there. I will steer clear of this method on the new canopy mold

I really appriciate all you mens input into this task.

Later