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Building Tips and technical articles. => Building techniques => Topic started by: Motorman on February 23, 2020, 09:24:36 PM
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Depending on the type of plastic in that Sig canopy, it might remember it was a flat sheet when you heat it up and try to go back to be a flat sheet with not too satisfactory results.
You might try Keith Sparks of Park Flyer Plastics. He has many canopies of all shapes and sizes.
https://parkflyerplastics.com/cart/index.php?main_page=index&cPath=46
Keith
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Or if you get really really desperate for your own perfect canopy search YouTube for "vacuum forming" where you'll find lots of videos of doing it in the kitchen with your oven and vacuum cleaner, or get in touch with Nick Ziroli models who will vacuum form over your plug for a reasonable (but hefty compared to a factory-made canopy) fee.
If it's for stunt, I'd just find something close...
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From experience I don't think you'll have much luck trying to re-form a ready made canopy. If you can't find or purchase one you like then you can mold your own. Somewhere here I did a thread a few years ago about doing this with simple tools and a small countertop oven. You might enter a search for that and get some ideas.....
Dave
Well I guess you can forget that. I tried and can't find it. Maybe after a time they are scrubbed.
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RC Modeler magazine had an article in 1996 on how to use a male mold and a 2 liter coke bottle with a monokote heat to shrink the coke bottle plastic onto the male canopy mold. I have used this technique from 1999 to make canopies for over 40 stunt ships.
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Tom may have more on this. I have used this heat shrink of a plastic bottle a number of time with satisfactory results. It is as simple as it sounds but as you suggest, there are some things to work out. Tom showed me how easy it is to do.
I assume you have made a pattern of the canopy you want. I have found basswood to work more than satisfactory and you do not need to finish it with resin or dope or anything. Just make it as smooth as you can, like with 600 paper. The form should be slightly deeper to allow for trimming, just as you would need with a commercial canopy. You will need to firmly attach a base to the form so it will fit really snugly in the bottle after you cut the bottom end from the bottle. The base should be much more narrow and shorter than your canopy form so it will not interfere with the shrinking process over the form. After you put the form/base in the bottle, jam tapered hard wood sticks between the bottom of the base and the bottle so that the form/base are firmly jammed in the bottle. Then take some clamps (like 2) and clamp the plastic as firmly as possible to the base. (The clamps work as handy handles when you start heating the thing.
Normally, you will want to put the forward portion of the canopy towards the "neck" of the bottle to accommodate/ease the shrinking process for that portion of the canopy.
It might take several attempts to get the results you want. Experimentation will show which way to apply the heat, like at the front first, then the sides, or other approaches might work best. You will find that there is a limit to how much that plastic will shrink. However, even if the heating appears that it will not shrink the material any more, continue to apply the heat and sometimes that last bit will work out. Just have to be careful as too much heat will cause the plastic to blister. After the shrinking as been finished, cut the excess plastic away and bingo, you have a custom canopy.
One neat thing about canopies formed this way is that the plastic material is shrunk from its original shape which means the resulting canopy shell will be much thicker (stronger) than most vacuum form canopies. Also, the material is totally hot fuel proof. It will not deform when leaving the model in a closed car under a hot sun as some vacuum formed canopies will become misshapen from the heat and the plastic tries to remember it used to be a flat sheet. You can paint these things just like a vacuum formed canopy.
Depending on the plastic bottle, there is a limit on how long the canopy form can be to get the shape desired on both ends of the canopy.
This is a really neat and easy process to get a canopy for some special shape or scale model.
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I'm not sure if I'm dumb or picky, but I've never been satisfied with the results I get from shrinking over a bottle.
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Keith covered the process very well.
Tom
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Keith,
Thanks for the Keith Sparks of Park Flyer Plastics URL.
T Michael Jennings
Knoxville, TN