How to get PETG crystal clear after vac forming ?

tiksie

New Member
Hi guys, long time reader on this great forum, ended up signing up a while ago to ask a question but lost interest in the project (haha).

I've since purchased some clear PETG after doing countless hours of research as I read that it has the best clarity out of all the plastics (this could possibly be wrong though!).

Anyway, I'm attempting to make clear headlight covers for my car and have been having the same problem which is pretty much a loss of clarity after forming over the mould.

The mould is made from plaster of paris which has been dried for a few months and sanded back with 600G sandpaper.


After reading this thread:
http://www.therpf.com/f9/vacuum-forming-clear-petg-problems-205666/?highlight=PETG

I formed a 1mm styrene sheet over the mould and then formed the 2mm Clear PETG over that after someone said that forming a 'skin' over the buck would get better results with the clear PETG, but the same problem is still occurring unfortunately.

Excuse the crappy phone photo's, I couldn't get the loss of clarity in the camera but I did turn the phones flash on which makes the small 'spots' and 'dots' cause a shadow over my palm:

96qT8li.jpg

SvL46wO.jpg


As you can see on the left side of the pictures, the waviness/blotchyness is much more apparent.

Any idea what I'm doing wrong ?

Cheers
 

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how long are you heating the plastic and at what temperature?

I'm actually using a 2000W patio heater in a box I built so I don't know the exact temp reading. The 1mm styrene takes about 30 seconds to heat whereas the 2mm PETG takes takes about 3 minutes (I just watch the sag and transfer it to the vac board accordingly).

Do you think it's overheating ?
 
I'm actually using a 2000W patio heater in a box I built so I don't know the exact temp reading. The 1mm styrene takes about 30 seconds to heat whereas the 2mm PETG takes takes about 3 minutes (I just watch the sag and transfer it to the vac board accordingly).

Do you think it's overheating ?

i can't say for sure but it's the first thing i thought of. i use .060" and .080" PETG quite a lot when i'm pulling jason masks and i've never had the issues you're having. i use a regular kitchen oven set to 325 degrees. the .060 takes around 2 minutes while the .080 takes around 3 minutes to sag enough for forming.

how deep is your draw? (the distance between the forming table and the top of your forming buck). if you could post a picture of your former and the buck you're using that would be cool. also, what's the size of the plastic sheets you're forming with? (length and width)
 
i can't say for sure but it's the first thing i thought of. i use .060" and .080" PETG quite a lot when i'm pulling jason masks and i've never had the issues you're having. i use a regular kitchen oven set to 325 degrees. the .060 takes around 2 minutes while the .080 takes around 3 minutes to sag enough for forming.

how deep is your draw? (the distance between the forming table and the top of your forming buck). if you could post a picture of your former and the buck you're using that would be cool. also, what's the size of the plastic sheets you're forming with? (length and width)


Thanks for the quick reply mate!

HlBVZaO.jpg



Not the prettiest looking thing haha. I have a hole with a pipe attachment on the bottom which is connected to my vacuum cleaner.

The buck I used is currently covered in the HIPS but here's another one that's exactly the same, just not sanded yet:
HF0izsI.jpg


table:
57cm long
24cm wide

buck:
39cm long
11cm wide
4.5cm high (so the draw is 45mm)

Plastic sheet size is the same as the table so 57cm long, 24cm wide.

For your masks (which are freakin' awesome!!) do you use clear PETG aswell ? The clarity issue (I'm guessing these are chill marks ?) is my main concern.

I wonder how people make clear motorbike visors!
 
your former and buck look fine to me. i guess the first thing i would do is try heating the plastic less. i've found that PETG is extremely easy to form and it really doesn't have to be really saggy when heated to get a great pull.

yeah i use PETG for almost every mask in the series. we've found that just about all of them were made of clear plastic. with the exception of the later movies.
 
Is it recommended to remove the protective film on the PETG sheets before heating and forming or is it possible to leave them on and then peel it off when you are ready to mount the piece? I want to minimize any scratching while I cut and sand the edges to keep the plastic crystal clear. So far i have been removing the film before hand, and i get some decent pulls that are clear...but it gets dinged up and what not when i cut and sand the edges and was looking to avoid that. any info would be appreciated!
 
When I pull a mask in PETG I have to trim and sand it and then scuff with a scotchbrite pad. When I've had to reshape the mask after all that's been done I've noticed that heat will turn the plastic clear again where I've scuffed it. I don't think that would fix deeper scratches but it has definitely fixed light scuffs. This was just a side effect when reshaping the mask. I haven't tried to make it clear again on purpose. Might be worth a shot on a scrap piece.
 
I disagree about removing the film before forming.
I always leave the film on while vac forming and pull it off afterwards.
Always get crystal clear parts.
 
I formed a 1mm styrene sheet over the mould and then formed the 2mm Clear PETG over that after someone said that forming a 'skin' over the buck would get better results with the clear PETG, but the same problem is still occurring unfortunately.

Does anyone know if I can use PETG rather than styrene?
I have a mold that was made my casting inside the original part, because the original part is significantly thicker over 1/8" and the PETG I am using is only 0.040" my external dimensions of the finished product are a little smaller than the original.

Can I pull one sheet of PETG over it, lightly sand it and leave it in place then pull another sheet of PETG over it and use that version or will using to sheets of the same plastic lead them to sticking together or anything.
 
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