acerc

Ok fellas, I "finally" get the difference. Was a bit slow in distinguishing it, but, I got it. Now that I do I also see why you guys that knew were so against the plexi. It is a hard brittle plastic in comparison to the poly's, definitely harder to work with outside of forming. That I can see from what I have already attempted. So I will give it a go with the PETG and if that fails I will try a sheet of Lexan.

acerc

Maybe one of you guys can tell me, of the two products Lexan and PETG, which has the least droop when heated for vacuuming?

acerc

Well, some more mind changing after speaking with the plastic company. This time when I called to order a sheet of Lexan I somehow managed to get a guy whom use to do blow molding and vacuum forming. He said that the Lexan has to be dried prior to molding and explained the what and why. According to him Lexan (any polycarbonate) has moisture within the plastic that will create bubbles when heated. After explaining what I am doing and how I am doing it he says that, even given that Plexiglas is more brittle, with my application the contours of the canopy along with the unlikely hood of something striking it just so he recommends the Plexiglas. The PETG has to much sag during heating in this manner and I don't have a drier for the Lexan. He also explained what and how in regards to cutting and drilling the Plexiglas. The special drill bit I ordered was shipped today, I have 5 more pieces of the Plexiglas, so I am going to stay the course with it. I will however give one of the sheets of PETG a go after I am done with the Plexi.

squirrly

My Feedback: (3)

Hi Robert, just when you think you got it, it throws you a curve. You'll get Bud, hang in there...Jeff

flyingagin

By the time you are done you will have given us all a 3rd year level college course on molding plastic
Thanks Professor Robert

Ken

John_M_

That's interesting Ace, I never heard of moisture in any plastic... you would think the temperature of the manufacturing process would drive any moisture out, unless its a cold process of manufacturing... of course I'm no expert, the gentlemen you spoke to should know his plasticology, would be interesting to learn how they dry it.

On youtube there are numerous videos showing RC car body, and other related vacuum forming using lexan sheet, but granted its probably only 1/16" of an inch thick or less.

Based on what I've read, the PETG is the better way to go, its the "go to plastic" for most vacuum forming... in the thicker sheets, the rigidity would be sufficient and not easily deformed when pressed on, definitely a lot more rigid than an soda bottle... and its a lot tougher than lexan in regards to repeated folding back and forth before it fatigues, it may not be bullet proof, but it has more resilience to cracking under constant flexing.

Why are use concerned about the droop during heating... watch some of those youtube videos, they are basically using the same setup as you for heating the plastic, and they don't seem to have any issues dealing with the droop.


John M,

acerc

I would assume the moisture may be of no issue at thinner sheets, I don't really know. The droop issue is this, when I heated the previous .040 PETG there was a good 7" droop and it still was not hot enough to fully vac down around the canopy mold and that was a much smaller size sheet. It may have been the oven was not working that well in that form, I don't know. All I do know is that I had troubles with PETG, I pulled one with the Plexi, I now have a better oven set-up, and I also know I am not done trying. When I head back Sunday I have to stop by Lowes, they have sheets of Lexan and I will pick one up for a test run. By the end of next week I will have tested Lexan, PETG, and pulled one from Plexi , at that time I will know which way works. Quite frankly due to the plastics characteristics I hope it is the Lexan, it is far less breakable than the Plexi and far stiffer than the PETG. I have my Pitts, the kit in the box, and a couple guys that would like one, plus I want to figure it out for future builds. One thing always bothered me and that is buying a canopy and then having to cut it and hope all went perfectly. Once I get this figured out, and I will, I will not have to worry about cutting a canopy again. Or replacing one.

LarsL

I have familiarity with plastic as I worked at a major motorcycle manufacturer and all of our bodywork & windscreens were made from "plastics." In the injection molding of plastic it is part of the process and necessary to dry the material before processing it in the injection molding machines. Same with rotational molding. In terms of Ther****rming which includes vacu-forming drying was not an issue. Perhaps if the material was sitting around for a real long time it could absorb moisture, but once in sheet form, I did not understand it to be hygroscopic. It wouldn't be the first time if I am wrong about that.

Lars

acerc

According to the guy they have a big oven that the sheets are hung in, the oven runs at around 400° for a couple days, and the oven has a vapor evacuation system, at least that is what I was told. Is it truly necessary at, or for, our needs? I have no idea. But come this time next week, at least in my application, I will know what happens.

John_M_

Well I went looking for more info as I usually do when I get curious... apparently lexan is hygroscopic and can absorb moister not only during the manufacturing process, but also while in storage... his drying temps seems a bit hi, as the info I got off the web, you can dry in an over at a temperature not exceeding 125C (257F) and should be held at above 200F for a few hours to drive off any moisture in the lexan sheet ... the heating temp for vacuum forming is 350F-360F, well above the boiling point of water and if the lexan contains moisture, as the lexan begins to soften, the moisture boils and causes bubbles to form in the lexan, so drying is essential before heating to the forming temps in order to get a bubble free form.... so I would say its "truly necessary" as you stated

It sounds like its more of a headache working with lexan without the proper equipment... I think you've got what you need, and go with the plexi, and if you still have issues with cracking, then settle for the PETG in a thicker sheet.



John M,

acerc

Exactly, and the drying requires the sheet to hang, elsewise it would stick to what it is laying on. I can put a sheet, corner to corner, in the oven I made and maintain a temp for drying. I, like you, thought the temps he mentioned were to high. I feel something just below vacuum softening temps would suffice, like you stated around 250°, and is what I will try for a couple hours then go directly to heating for vacuuming. It's worth a try anyway, as they say "Nothing ventured nothing gained".
I already know I can do Plexi so a good effort at the Lexan and PETG is nothing lost, but maybe, something gained.

acerc

Here is a good article on the processes used towards polycarbonates. http://plasticsmachining.com/magazin...carbonate.html

John_M_

Without a doubt, you can't learn anything unless you try... I would let it sit at 200F for an hour, then bump up the temp for another hour or so... just don't get it too hot during the drying phase.

I like the idea of using lexan, the fact that its used for RW aircraft windscreens, it's like adding another element of scale detail ; not that anyone would know of course ... but you have to go with what works... if you can find a way of dealing with the droop of the PETG, in a .040, or .060 thickness, it should be pretty sturdy.


Good bit of info, Bookmarked


John M,

acerc

I realized shortly after posting above that at these drying temps there should be no reason I can't just put it on the oven the same as heating for vacuuming. I thought that article was very informative in dealing with the issues of working the plastic. To be quite honest I think the Lexan would be a better choice for a canopy, far less flex. I don't know about you but I have seen videos from the cockpit of an r/c aircraft and the canopy was always, violently, bouncing around. That is what I do not want, mostly because of the mount hardware, but also because I just don't like the idea of that kind of vibration. Regardless of what plastic I end up utilizing it will definitely be better and stronger than the original kit canopy.

John_M_

Yes, if you can heat both sides; at those temps it shouldn't get soft, so handling it shouldn't be an issue, maybe turn it over once or twice to get heat on both sides

With the plexi, it will have pressure points under each screw head... with the vibration, it may cause the screw holes to fracture... I've always been fairly impressed by the durability of those RC car bodies... in the same scenario, plexi would be like an egg shell.

if anyone can make it work, it will be you... I'm sure this moisture drying isn't going to be the monster its made out to be, just a little more prep time and discovery ... either the lexan, or PETG, both are tough enough... I think the PETG has the better long term durability though.


John M,

OLDFLYER2

My Feedback: (5)

Hi Robert, at legend aircraft we use a step bit to drill any hole in plastic (plex/poly) however 1/8" is the smallest tip on the bit. but it will not crack the material. Good luck .See you at Sun n Fun.

acerc

I have a plastic bit ordered, it is scheduled for delivery Wednesday. As for Sun N Fun, the guy whom asked me to show the Pitts has informed me it has to be dropped off and that I could not have a pass to enter. I am not paying to show the plane and I'm not leaving it for others to take care of, therefore I will not be there.

stevegauth30

That sounds like a load of bull to me. I wouldn't go either.

squirrly

My Feedback: (3)

What!! Might as well hand them the keys to the car too. Are you kidding me. Drop it off...Ya right. I was born at night but, not last night.
Jeff

WacoNut

That sucks,

I was asked to bring my WACO to the fall Fly-In several years ago at the WACO Museum and they gave me and the wife free passes and we also got a free WACO ride to boot. One good turn deserves another I wound up donating my 1/4 WACO to their museum for display.

Bummer they are treating you that way.
Later!!
Anthony

acerc

Well, it may very well be a misunderstanding, but that's how I read the email. Here is an excerpt of the response,

" Sun'n Fun doesn't make passes available for display airplanes of any size. The airplane would have to be brought in before opening day. Monday would be the best. You could then take the trailer back home. You can pick the plane back up any morning before 8:00 AM.

We would love to have the airplane if this would work out for you."

WacoNut

Not a very good arrangement for sure.

No one in their right mind would leave their model unattended for any length of time not to mention having to pay to have it there as well. Bummer you will miss out on a great opportunity for you and your model.

Now fly the thing.
Anthony

John_M_

Doesn't sound like "Fun" in the sun.. how the hell does anyone attend... is it just for certain people... I'll agree with Anthony and Jeff, who in their right mind would just hand over something of that value to someone else and leave... and then "take the trailer back home" !!.. that's like opening the door and inviting home invaders into your home, serve them dinner, and hand them your possessions when they leave... I've never attended any model show, or event where the owner is not present with their aircraft.... his logic is dumbfounding



John M,

stevegauth30

you'll have your fun in the Sun with that thing brother. who knows? Maybe it's an omen.

Cub Flyer Fresno

Hmmm... do I detect a boycott of Sun N Fun in the wind? I for one am not going!