Vacuum form a clear canopy!
 

Saw some posts on forming a canopy, so I thought I would post my experiences in trying to form the perfect canopy! If any of you know me then you’ll know I am a perfectionist, it can be miserable because NOTHING is good enough! This may help some in their quest for a truly clear canopy. If you are happy with something that looks kind of clear then make a plug out of anything you want and get forming! For others that want to make a canopy that is of a commercial quality, it can be done in your kitchen. With some luck and paying strict attention to the details, you can do it. I needed a canopy for my current project, an F2G Corsair. I redrew the Royal Corsair plans with all the changes needed for the conversion.

I used PETG for this canopy, very strong and forms well and it can make a very clear shiny canopy if you have the proper plug. I have used .030 and .040 PETG, they both work well, use .030 for the smaller stuff. I get my plastic locally from Piedmont Plastics [link=http://WWW.piedmontplastics.com]Piedmont Plastics[/link], it comes in sheets .040x48x96 for $21.76 each. When you consider that Lone Star Models sells a 12”x24” sheet of this for $3.75, that would come to $60! I can make 16 canopies for $21, when you first start though you won’t make 16 usable canopies!

1. First we have to make the plug, I prefer plaster because it is easy to work with. Here is how I make mine. I first make the top of the fuselage with a 1/16” ply piece stuck in the top that has the profile shape of the canopy. It is then covered with Monokote and the canopy is sculpted in clay. This allows great freedom to make changes until I am satisfied with the final shape.

2. We need to make a mold from this clay plug to make our final plaster one. I made a small dam around the sculpture, sealed the base of the form to keep the plaster from going under it. Cover this with a thin coat of plaster, I like to brush on a thin coat and then dip paper towels in the plaster and lay them on to build it up quick.

3. When you pull the plaster off of the clay form this is how it should look if you did it right. Grease the inside lightly but completely with Vaseline and fill it with plaster.

4. When that dries just break the mold off of the plug, that way it won’t get damaged.

RE: Vacuum form a clear canopy!
 

1. This is how my plug looks ready for forming, at first I covered the whole thing in styrene, but I like to have an edge for cutting that shows up well. This plug is covered in resin, but it is not necessary, you just need to form .040 styrene over your plug first, this is ONE of the keys to a totally clear canopy. Form it, cut it to shape then spray the back with 3M spray adhesive, then carefully stick it to the plug. Give it a good wet sanding with 600 grit sandpaper, this is a very important step, it has to be smooth.. NEVER use anything on the plug, don’t touch it with your greasy fingers either!!! Let it sit for an hour after sanding to make sure it is totally dry in the area where you will be forming your canopies. Don’t let it dry outside then bring it inside and start working on it, the temperature change could cause moisture to form. ANYTHING on the plug will cause it to be a bad pull.

2. You will need a tack cloth and have the wife do a good job on cleaning the stove, when you pull the protective backing off of the plastic you will be amazed at all the crud it will pull out of thin air! Or how the smallest piece of fly dung can totally ruin your otherwise perfect canopy! I wipe the plug down good and also the plastic.

3. When making things with white styrene the placement in the oven in relationship to the heat source is not an issue, but that’s not true with clear PETG! I use the broiler to heat the oven, turn it on and close it so that the oven will get heated up. Put the plastic in about the middle, if it’s to close to the heat it will melt to fast and holes will form very quickly. Keep a close eye on it and when it sags about 21/2 or 3” it’s ready to go.

4. I like to have my 6hp shop vac already running when I put the plastic on the plug.

RE: Vacuum form a clear canopy!
 

1. Let the vac run about 10 seconds or so but do not touch the plastic! It is still soft and you will leave fingerprints in it or make it uneven! I have not had it stick to anything at all, just pull on one side then the other, out away from the plug and it will pop right off.

2. It’s hard to demonstrate clarity in a picture, but this is a finished canopy. I’m very pleased with the results, good luck with your projects!


Dion

RE: Vacuum form a clear canopy!
 

peace

RE: Vacuum form a clear canopy!
 

Dion. From the looks of your plastic frame and fasteners, we might have read the same book.

This was my first attempt at vacuum forming. The task was a challenge, but the results were gratifying. I glued up the flat pieces, turned it upside down, filled it with plaster, shaped the "dome" and pulled the plastic. Instead of molding the frame into the canopy, I pulled two canopies, cut out the "windows" in one, painted it and glued it in place.

Les

RE: Vacuum form a clear canopy!
 

Nothing beats an informative thread and some nice photos.

Thanks for sharing your results with us. This subject comes up a lot here, and your parts look good.

RE: Vacuum form a clear canopy!
 

Thanks very much for this 'how to'. I've been holding off making my canopies because I wasn't quite sure how to do it, now I do.

-one question though, after you make the plaster plug, do I have this straight that you cover the plaster plug with the styrene? Then the styrene makes the clear canopy smooth and doesn't melt from the heat?

thanks again.


Kelvin.

RE: Vacuum form a clear canopy!
 

Kelvin. I have not done that, but the intent is: the surface of the plastic that touches the mold will take any and all distortions in the mold, but the outer surface will not. It will stay smooth, so the next part you pull will have a near perfect surface.

Les

RE: Vacuum form a clear canopy!
 

Dion,'
Great stuff, thanks!!
couple of quuick questions..

The frame to hold the plastic, is that just Aluminum angle?

Does the depth of the Vacuum Box make a difference in making a good pull (4" depth is better than 2"?)

What is black on the top of you vacuum box?

Thanks

RE: Vacuum form a clear canopy!
 

YAT: Micro Mark sells a book for about $15.00 on vacuum forming, that is well worth the price. Answers all of the questions that you haven't even thought of yet.

Les

RE: Vacuum form a clear canopy!
 

Thanks Les for adding your canopy technique! I agree that the easiest and best way is to add the frames later with a thinner white styrene. I wanted to make my canopy look more commercial, and having ridges built in makes it stronger, but again it's not necessary. Your's looks very nice!

Good question Kelvin, in my experiments if you pull .040 white styrene over the plug and sand it, then glue it on with 3M spray adhesive it will last for up to 3 or 4 pulls before it has a tendency to bubble. If you get the PETG to hot and over the 120 degree working temp then it could harm the styrene you have on the plug. If you use a lighter PETG like .030 and .040 white styrene on the plug then you can pull as many as you want, I never found the limit and I made a bunch of them. It's when you have the same thicknesses on the plug and clear that you will run into problems after a few pulls.


YAT-28E I got the frame idea from Chad here on RCU, it's just aluminum angle bent and pop riveted, works great.

You should not make a deep box, the less air your vacuum has to take out the quicker it will draw the plastic. In fact you don't need a box at all, just a board with a hole in the bottom. You will need to use small sticks or something to keep the canopy up so it won't block the vacuum hole. Use weather strip as a seal. My box is about an inch and a half deep and it works great.

The top is 1/8 inch tempered Masonite, I took the time to drill all the little holes! It's important to have enough holes in the top for a good pull, also it must be supported from the bottom with some small posts.


Wish I would have got the book instead of learning on my own! Here are my latest experiments with plugs, one major failure to report! I thought that I would first cover the plug in resin, spot putty and primer, got it real smooth (should have stopped there!). Next I painted it with Ford Blue engine paint, it says it takes the heat, up to 500 degrees, what I didn't know was that it also sticks BETTER than glue to PETG plastic![X(] Look at what it did to my plug!

Next picture, what kind of advanced finishing system would one need to finish a plug for a clear canopy? You must be thinking that it's some space age finishing system? NO! Try Wal Mart $1.79 a can dirt cheap primer, Brite Touch! I was getting frustrated so I finished the Corsair canopy quickly, first I cover the plug with finishing resin, hit it with some primer, not even finishing it with more primer, just got it real smooth... it worked! I could not believe it, I had my other plug in the same primer and if I had just sopped there I would have had a perfect plug for forming[:@]!

Well that's it on this, if I do anything else I'll post it here. Please post your work on this thread also, I would like to see what others are doing, maybe we can learn some new techniques!

Thank you everyone,

Dion

RE: Vacuum form a clear canopy!
 

Dion: According to the "book". One fair size hole in the middle of the "floor", and window screen to allow vacuum distribution, allows you to use different sizes of frames. Since I have gotten heavily into electrics, many of my parts are small, and I don't want to use a full sheet of plastic, and frequently don't have enough to fill up a large sheet.

Les

RE: Vacuum form a clear canopy!
 

Great idea Les, then all you have to do is make several size frames and screens, much easier!!

Has anyone seen the new October issue of Model Airplane News? Great article on page #116, I have one question though: What is Molding Compound? If anyone knows could you tell me where to get it, I would appreciate that.

Dion

RE: Vacuum form a clear canopy!
 

Speaking of Model Airplane News, there's an article on making cowls from transparent bottles. I was about to try this but I thought it better to look around before I did. The pics looked good, so after a while of open-cockpit flying I set it all up but, of course there's a "but", the bottle was too big. So instead I attempted to make a canopy for a P-40 (including the rear windows) using a method similar, in a way.
1. Utilizing a solid plug, any material, (the same plug I was about to use for the bottle thing) temporailly or permanantly attach it to a board that is about 2-3" wider on all sides of the plug (plug bottom fuz side down), lay a piece of plastic sheeting over the whole thing and clip it in place tightly.
2. With a heatgun on high, start melting the plastic over the plug, the plastic will shrink, the only real problem is that the corners overlap, I tried to fix it, but before I ruined it I stopped-still looked alright though. The less important problem was that the plastic was too thin, it broke before it ever got in the air.
3. Once the plastic cools unclip it and remove it from the plug. Trim excess and add frame lines. If anyone else uses this idea let me know if you get the folds out of it, also if someone uses the bottle idea either. Thankyou.

brED

RE: Vacuum form a clear canopy!
 

I didn't have any wrinkles, but I couldn't find a glue that would work reasonably, either.

Les

RE: Vacuum form a clear canopy!
 

;) Good info here:

http://rcalbum.rchomepage.com/Home.html#Wellington

RE: Vacuum form a clear canopy!
 

That "Radio Control Modeling in Nova Scotia" is a great site.

Also try "molding compound vacuum chamber" in Google.

I have used "Perma Stone" to make plugs. Available at local crafts store.

RE: Vacuum form a clear canopy!
 

Is that stuff expensive and does it form a clear part? I have found that all that's needed is to use plaster and seal it with cheap primer. Make sure you wait a few days for the primer to completely dry, give it a 400 grit sanding. I can pull very clear parts using this method.

RE: Vacuum form a clear canopy!
 

diony:
Sorry I didn't read your first post closely enough. "...post my experiences in trying to form the perfect canopy!..."
The Perma stone is less than $10 a can to try, but looking at your finished canopy, not as good as your method.
I like it because it is a lot harder than plaster, ready to use the next day without coating and produces a not-bad result.
The missus is around so I have to wait awhile to use the oven to try to form a new canopy to take a picture of.

RE: Vacuum form a clear canopy!
 

I found wrinkles in the procedure I did that was similar to the bottle method. But I'm glad to see that someone used the bottle method.
brED

RE: Vacuum form a clear canopy!
 

Haha:D That's good that it's stronger than plaster, won't chip. I would think that all it needs is a good coat of primer and a good sanding with 400 grit, then it would be perfect. You should try it, I would like to see your results. Just make sure that you let the primer fully dry over a few days. I am going to do some experiments with Bondo, I am thinking that it will be very smooth and not need to much prep work.

Dion

RE: Vacuum form a clear canopy!
 

Would a fiberglass plug work?

I was thinking I could lay up a few layers of glass in my mold then fill the rest with plaster. The parts that currently come out of the mold are exceptionally smooth, what ya think? or would it be too hot for the resin?

RE: Vacuum form a clear canopy!
 

Good Idea, I think it would work great. My Corsair plug is plaster covered with epoxy resin. I just sprayed some auto primer on it and sanded most of it off with 400 grit, basically what you want to do. Do one and post the results!

Dion

RE: Vacuum form a clear canopy!
 

I don't know if it still is the norm but, at one point in time, many manufacturers were making their canopy plugs from Bondo. You might be able to pull a mold with thick styrene or ABS and fill it with Bondo. I'm just not sure if the plastic will take the heat generated during the curing process. If it worked you would then have a solid (or hollow, if you desire) Bondo plug which could be sanded to a near perfect finish. I suppose you could pour it into a plaster mold also, if the plastic doesn't work. I've seen several very nice (and very large) canopy plugs made this way and the quality of the parts pulled over them was outstanding. The one that comes first to mind is the Rick Lewis designed Skyraider with which several well known modelers competed some years back.

PS- Bondo is a polyester product and can be thinned down with polyester resin for pouring purposes.

RE: Vacuum form a clear canopy!
 

Hi Chad, thanks for that info on the Bondo, I just went out a bought a huge tub of it! I will try to thin it, that was one of the things I was concerned about, having lots of bubbles. I'm sure it will work great, pouring it in a formed styrene mold might be a problem, but thats the first thing I'm going to try. It might have it's shape before it gets to hot, then it won't matter if the mold warps, we'll see.

I'll post here soon with my new bondo plugs and canopies!

I know you're not working on anything now Chad, but what is the wingspan of that Corsair project you have? You told me once I just can't remember.

Thanks again!

Dion