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PETG visors part 2

 
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jegner
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PostPosted: Tue Aug 01, 2006 12:55 pm    Post subject: PETG visors part 2 Reply with quote

Well, I've been working some on the new visors for the RFT helmets. Here is what I have learned:

PETG is pretty easy to work with, but you do need to watch it closely, as the range of time it goes from too stiff to just right to over heated is pretty fast. Also, it takes twice as long as HIPS to cool down hard enough to demold.

Use a bandsaw to trim the PETG out. Then Dremel it with a sanding drum to clean up edges.

I now have the prototype X-wing helmet visor ready to dye amber. This PM if I am lucky I can demonstrate this process on camera.

The PETG is expensive, and does seem to blister easily, causing defects in an otherwsie clear surface. Not sure what causes that, as the molds were dust free. Lint in the air? Humidity? Unknown.

Jim
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AlterEgos
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Location: Centreville, VA

PostPosted: Tue Aug 01, 2006 2:38 pm    Post subject: Reply with quote

What thickness of PETG are you using?

I've done some test pulls of some .060 and haven't had any noticeable distortions or defects, only major webbing problems.

I'm certainly no expert, but it's very possible that your issues may be due to humidity and the high heat combined. It seems that PETG will absorb just about anything at its melting point. In fact, I think most clear plastics share this property... probably because of the type of polymers used in their construction.

And you're right, that stuff really likes to hug your mold!
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jegner
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PostPosted: Tue Aug 01, 2006 8:45 pm    Post subject: Reply with quote

It's either .080 ro .093, and yes, webbing is BAD with that stuff.

Looks like a 150-160 degree hot water for dying is hot enough to set the RIT dye, but cool enough to avoid the warping. However, if you don't get the water hot enough, the shade of gray will have more 'red' in it, leaving a real smoked glass look. LOL.

Oh, well.

Jim
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badger
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Joined: 03 Sep 2006
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PostPosted: Sun Jan 14, 2007 12:50 am    Post subject: Reply with quote

going through older posts.

Hey Jim, I found a can of a spray for "stained glass" in a great orange color that worked very well on PETG visors. I found it at micheals, a craft store here.

If it's something you still need info on.
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jegner
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PostPosted: Sat Jan 20, 2007 4:59 pm    Post subject: Reply with quote

I've seen that stuff at the hobby store. I wonder, how well it works. Anyone ever use the stuff?
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badger
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PostPosted: Sun Jan 21, 2007 7:44 pm    Post subject: Reply with quote

Quite nicely.

[img]http://images17.fotki.com/v4/photos/4/42813/3678388/AM2-vi.jpg?1150648573[/img]

(that's Anne McAffrey in the foreground, woo!)
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jegner
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PostPosted: Thu Feb 22, 2007 10:56 am    Post subject: Reply with quote

Cool!

Is that sprayed on tint?
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AlterEgos
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PostPosted: Thu Feb 22, 2007 11:57 pm    Post subject: Reply with quote

Hey Jim, had any luck with getting better pulls with PETG? I was thinking of using a negative mold, which might help the webbing problem, but haven't gotten around to making one yet. Perhaps in a few months... what do you think?
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drcrash
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PostPosted: Fri Feb 23, 2007 12:01 am    Post subject: Reply with quote

AlterEgos wrote:
Hey Jim, had any luck with getting better pulls with PETG? I was thinking of using a negative mold, which might help the webbing problem, but haven't gotten around to making one yet. Perhaps in a few months... what do you think?


John, could you post some pictures of your stuff with webbing problems? I'm working on a methodology for diagnosing & fixing webbing issues, and pictures could be enlightening.
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Tired of buying cheap plastic crap? Now you can make your own! www.VacuumFormerPlans.com
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jegner
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PostPosted: Fri Feb 23, 2007 7:21 am    Post subject: Reply with quote

IMHO, PETG needs to be predried, just like ABS. It also really needs tighter temp. control than HIPS. That stuff goes from still too rigid to pull, to super saggy, almost too soft almost immediately, one reason for the webbing. You really have to watch it.

A negative mold might do the trick. Just be sure your mold is super-duper clean, any traces of, say talcum powder, or even sawdust, and it gets transferred to the plastic. Downside to pulling clear.

My next PETG experiment is to dye the pastic, before the heating cycle, and see if that helps set the amber dye.

Jim
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AlterEgos
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PostPosted: Fri Feb 23, 2007 9:40 pm    Post subject: Reply with quote

Paul:
Well, I pulled a couple of PETG pieces long ago and I don't think I have them any more (probably threw them away), but I'll look around the workroom and see what I can find. Neutral

Jim:
How do you pre-dry PETG (or ABS for that matter)? I have a voltage regulator on my oven, so temp-control isn't a problem. Wink

Once I get my workroom re-organized, I'll jump back into the swing of vacuforming. It's just that the mess in it right now is so big that I don't have any room to work. I'm sure you all can relate. Laughing
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jegner
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PostPosted: Fri Feb 23, 2007 9:57 pm    Post subject: Reply with quote

Dr. Crash might have more technical details, but as I understand it, for ABS anyways, just make a box, with some 100W lamps, then sweat those sheets for a couple of hours under low heat, 180 degrees F. or less.

Jim
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