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remarque · Posted: Tue May 08, 2007 10:23 pm Post subject: I need little help

You all have seen my 16X24 machine, I have since sold it and build a 24X24, with two 10 gallon tanks, a gast vacuum pump ( I can get down to 23 in) and I went with a flip top design.

Here is my problem. I'm trying to form the housing for my tail lights using 0.060 ABS, when I flip the plastic over the mold it forms about 10% of the sides, then the plastic refuses to go down any further. I've cut holes in the bottom of the mold to allow air to get out of the mold and it still gets stuck.

The mold is made of fiberglass that is reinforced with wood. It is about 16in long and 12in wide and 6in deep.

Does anyone have any advice?

crashmann · Guru Joined: 27 Sep 2005 Posts: 501

Does your plastic holding frame go all the way down around the platen? It sounds like you're not getting a good seal between the platen and the plastic (Dr Crash re-posted information about that in this topic: http://www.tk560.com/phpBB2/viewtopic.php?t=462 )

Is the ABS warm enough to pull all the way down over your mold?

While warming up your oven, put the mold on top to let it heat up. Keep the mold on top of your oven while the plastic is heating, then put it on the platen just before the plastic is ready.

Do you have the same trouble when using HIPS or other material?

Show us a picture of the pull (or lack thereof) on your forming platen so we can see what is happening.

Charlie
TI-386

remarque · Posted: Wed May 09, 2007 8:20 am Post subject:

Its not the frame I've formed the lense using .090 PET-G and it formed really good, so I know I got a good seal.

I heat the plastics up until it start smoking, then form.

Here is a picture of my so called from.

drcrash · Posted: Wed May 09, 2007 9:14 am Post subject:

mr2monster · Newbie Joined: 05 May 2007 Posts: 22

I think you said this, but in an effort to clarify.... you drilled escape holes in the negative cavity of your mold in the deepest spots correct?
_________________
making stuff is cool.

drcrash · Posted: Wed May 09, 2007 12:24 pm Post subject:

Aside from the issue of cooking it too fast and burning the surface, it appears to me that you are either not maintaining a good seal & getting good suction, or you didn't heat the plastic long enough, and it's not done through.

Did it sag substantially before you formed it? ABS will probably need a bit more sag than PETG, because it's not as easy to form.

I often touch the plastic with a gloved finger to feel how rubbery it is, as well as observing the sag to tell me when to go for it.
_________________
Paul (a.k.a. Dr. Crash)

Tired of buying cheap plastic crap? Now you can make your own! www.VacuumFormerPlans.com

remarque · Posted: Wed May 09, 2007 12:39 pm Post subject:

It takes about 1 to 2 minutes before it starts to smoke, it may be that I'm heating it to fast. I try heating it slowly today and see if it works.

faithblinded · Posted: Wed May 09, 2007 2:34 pm Post subject:

drcrash · Posted: Wed May 09, 2007 4:17 pm Post subject:

It's kinda hard to see what's going on in that picture... are areas of the plastic seriously boogered up, or are those artifacts of the photo flash or something? (Are there any tears in the plastic? Just checking.)

There appear to be warps in the middle of each edge. I don't know if that happened during the pull or after, but I'm wondering if the plastic or frames sealed to the platen or gasket.

It looks like you're using frames and a gasket, where the bottom frame meets the gasket. Keep in mind that with that kind of arrangement, the plastic must be tight against the top of the bottom frame, as well as having the bottom of the frame tight against the gasket. Any chance the upper frame bowed more than the bottom one, and let a gap open up between the plastic and the bottom frame?

Could you post pictures of your frames, and your buck sitting on the platen? It's hard to guess what's going on without seeing the machinery.
_________________
Paul (a.k.a. Dr. Crash)

Tired of buying cheap plastic crap? Now you can make your own! www.VacuumFormerPlans.com

jegner · Posted: Wed May 09, 2007 6:47 pm Post subject:

ABS can be harder to form that HIPS, but PETG is about the same level of difficulty as ABS. If the ABS is smoking, your oven is too hot.

Test your pulls with HIPS, also, 10 gallons is not enough storage capacity for a 24x24 platen, you need 30-40 gallons, so you may just be running out of vacuum before the plastic has time cool.

Can you show us a pic of your mold? Sounds like a negative mold, and if so, you will need more vacuum storage. Test with HIPs and a shop vac, and let us know how it does.

Jim

remarque · Posted: Wed May 09, 2007 7:02 pm Post subject:

There are no tears in the plastic, its just the flash from the camera.

I'm using 20 gallons not 10.

I believe I've found the problem, since the PET-G was thicker than the ABS is was able to press tightly against the frame and thus get a good seal. I found that two of my boards that I used to make my top frame are warped a little. I'll more than likely rebuild the entire frame just to make sure it holds tight and use to two clamps to lock it place instead of one.

Thanks for the help.

I'll post picture tomorrow of my machine.