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Old 07-23-2019, 11:40 AM
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Here is a canopy made from the same foam. This one I covered it with iron -on ChinaKote. For this airplane I didnít shape it well. You can see the flat top. It takes the iron-on covering well but you canít use too much heat.

For a clear canopy the plug needs to handle the heat really well. On my test foam I have a Fiberglas side and a resin only side. Once I top coat it Iíll test to see how both sides handle the heat.
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Old 07-23-2019, 12:27 PM
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If the canopy has no concave shapes, you may want to consider just pulling it over a male plug. In this case you pull the canopy farther than necessary and trim off the excess. The plastic is attached to a perimeter frame for the pull. Many commercial canopies are a combination of pull and vacuum. Wood seems to be the best material for the plug. Bare if you are a good carver / shaper. Finished with high temp epoxy if necessary. Canopies are a PITA even for production people. Part skill and luck with a bit of experimenting at all levels.
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Old 07-23-2019, 09:28 PM
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Truckracer, I guess I may not have been clear. The foam canopy will be the male plug. I will pull it as you describe. Iím just working on the plug for now. Will move on to the heater and vacuum box later.
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Old 07-23-2019, 09:40 PM
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I have never heard of using foam for a male plug unless it was the base of a hard shell of fiberglass and / or high temperature epoxy. I have visions of the foam becoming a puddle as soon as the hot plastic hits it. My point was that for simple convex only forms, in many cases no vacuum is necessary.
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Old 07-25-2019, 09:24 PM
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Quote:
Originally Posted by Truckracer View Post
I have never heard of using foam for a male plug unless it was the base of a hard shell of fiberglass and / or high temperature epoxy. I have visions of the foam becoming a puddle as soon as the hot plastic hits it. My point was that for simple convex only forms, in many cases no vacuum is necessary.
Never done it, But have been watching a ton of utube videos. they say the plug needs to be able to handle 300 degrees/. if you use foam it needs to be coated in something.
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Old 07-26-2019, 08:40 AM
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I have seen a few foam plugs used for forming. So, I finished shaping the canopy. Then I covered it with fiberglass. Iíll add a second coat of resin today. You need very sharp cutting tools for the fiberglass. Over the fiberglass will go the top coat finished for the pull. It provides the heat barrier. Iím looking at DURHAMíS Water Putty, general purpose Bondo and automotive Bondo. Iíve tested the WP in soda bottle forming. Need to test the general Bondo. Automotive Bondo is a bit harder to work with.

My test panel has a fiberglass side and a resin only side, covered with Bondo and WP. THE Bondo sanded really smooth with 220 paper. I need to apply the heat to see what happens. Iíll also heat the leftover hardened resin. Finally Iíll drape some plastic over the test panel. Iíll just keep plugging along. LOL.
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Old 07-27-2019, 07:41 AM
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This canopy came out pretty good. The weave is filled. You can just about finish sand it, primer and paint. And put it on the airplane. It may be an option. LoL. It weighs in at 2 7/8 ounces. Strong as can be. Now it is on to heat testing.
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Old 07-27-2019, 04:49 PM
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Well, the heat test was inconclusive but promising. When I first applied heat, the water putty started to break apart, as you can see. It was a thin layer but so was the Bondo. The Bondo never cracked but it did develop some bubbles. I attribute this to the poor test piece I made up. I never sealed the sides and there was a joint where the water putty met the Bondo. So I had some melting on the sides and in the joint area. I think this caused the bubbling. The Bondo on the right side was over fiberglass and it held up good. What is surprising is the blue foam on the right side. It only had 2 coats of resin and it held up well. Temperature reading was with an infrared thermometer, up to 300*. Also it was constant heat. Not what you would have with vacuum forming.

Iíve made 2 new plugs to further test the Bondo, household and automotive. These will be properly sealed. Iím sure Bondo will work. Just have to see which one works better.
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Old 07-27-2019, 10:57 PM
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It looking good.. those other tests sheets don't look so good. wow .. kinda melted it.
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Old 07-31-2019, 06:43 PM
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I found that I did not have any auto body filler. I didnít want to buy any so Iím going with just the all purpose Bondo. I made this plug with fiberglass on the left ĺís and no fiberglass on the right end. Both sides covered with Bondo. The Bondo sands easy and smooth. This is not a final sanding finish on the Bondo. Just a working sample. I made a small vacuum former and tested with my shop vac using a plastic bag. I need to make the frame to hold my plastic test pieces then Iíll try a pull on this work piece. Hope all goes well. Just learning as I go.
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Old 08-01-2019, 12:14 PM
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Not wanting to be overly critical of your search for information, but why not just carve your plug from a soft wood such as Bass, Poplar or soft Pine? Finished with fine sandpaper, you could pull your canopy (or vacuum form if you're set on that) without having to finish it at all. It would also be easier to mount on a fixture for the pulling or forming process. Seems like a whole lot of work going on here that resembles reinventing the wheel.
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Old 08-01-2019, 02:24 PM
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On a side note, with limited vacuum from a shop vac, would a strong heat gun be worth having handy when pulling the mold as a helper?
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Old 08-01-2019, 06:19 PM
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Originally Posted by Truckracer View Post
Not wanting to be overly critical of your search for information, but why not just carve your plug from a soft wood such as Bass, Poplar or soft Pine? Finished with fine sandpaper, you could pull your canopy (or vacuum form if you're set on that) without having to finish it at all. It would also be easier to mount on a fixture for the pulling or forming process. Seems like a whole lot of work going on here that resembles reinventing the wheel.
Primarily, I want to try foam. Wood is good for those who want to use it. Just experimenting here. There are other things besides canopies to be done.
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