Vaccum forming help, please!!

[Grinn3r]

I'm new here and I've finally gotten my homemade vaccum forming machine set up... or at least, that's what I thought.


My setup uses an electric griddle (14" x 14"), a wooden box with perforated board as the top (14" x 14" x 2"), two metal frames that I clip together (12" x 12"), and an old shopvac.



In addition, I bought two sets of plastic: clear Polycarbonate (12" x 12" .01") and black ABS (12" x 12" x 1/16")

My intention with the thicker plastic is to make masks and other props with, but preferably with the smooth side up.
The thin stuff was more of a flub on my part thinking it would be thick enough...

So I hooked this all up and put the form I was going to test the plastic I bought with. A simple plaster face mold.
Alas, neither of the plastics I bought worked.
First I heated a sheet of the ABS on the griddle at the recommended temperature of 325-350 F, but just when I thought it was ready, I pressed it down over the form and got... this:


So, of course, this made me decide to try again with the thinner plastic instead to test and see if I could get it. Its heating temperature is higher, 360-400 F, so I assumed it would be more forgiving..
But... even though it became transparent and sagged some, it was as if it lost all added heat after I took it off the griddle and refused to take ANY of the form.
Then I decided to tape off the majority of the holes outside the direct area surrounding the plaster face in hopes that it would make the uncovered holes pull stronger.

I attempted to add the use of my grandfather's new heatgun to heat the top of the plastic more to temperature. Which may have been because of my impatience or frustration, but I was met with no success then either.

For anyone that knows a lot (or at least more) about this, could you give me some pointers?
I really want to know what all I'm doing wrong.
What temperature should I set these to?
How long do I wait until these are heated sufficiently?
What strength does my vaccum need to be to make this work?
How much time do I have to get the plastic off the heating element and onto the form?

Any immediate response would be greatly appreciated, my project deadline is a few months away, but I just really want to get this solved as soon as possible.

 

[ultraman]

i had similar things happen when a buddy and i were using the same things you are.

1) we were using a toaster oven and having no luck until one day we raised the heat temperature ...apparently these "plug in the wall" appliances suck for telling accurate temps.

2) another shared screw up we had with you is i can see by the pictures that your frame doesn't over lap the outside of your vacuum box !
with the air escaping under your frame the plastic is cooling off before the suction takes hold....or your losing all suction under the frame because it's sitting on top and not wrapping over!

3) the block you are forming over ....it's best if its hallow or has holes drilled through it at the low spots like say the corners of your eyes on that mask block ....this makes it so the plastic can suck down into the low spots.

it always takes a lot of tests to tune your home made set up......don't give up!

and welcome to the site!

 

[Endless Wonder]

How in the world are you heating the plastic with the griddle? Are you actually laying it ON it? :confused I've never heard of this method.

How thick are your plastics? ABS is tricky to heat evenly and it's actually easy to overheat it and then you end up getting an orange peel texture.

Ultraman is right in that drilling holes all through your buck will help with getting better pulls. Though in the case of your face buck, it's not necessarily a must. The face isn't highly detail, nor is it very deep.

Something else I would recommend is laying down some weatherstripping on the box that is the same size of your frame. This will create an airtight seal when you lay down the frame over the buck and you'll get a much better pull.

Also, what horsepower is your shopvac? I can't see in the pic, but I wouldn't use anything less than at least a 6 horsepower.

 

[clonesix]

Problem: Wrong Plastic, ABS. Wrong Heat Source, Griddle.

Solution: Right Plastic = High Impact Styrene (HIPS) Right Heat Source = oven (makes kitchen smell!) or at least a quartz garage heater. You need even heat over entire surface area.



ABS plastic is extremely temperamental. It has a very narrow temperature window, and is quite unforgiving. HIPS is very forgiving, and will work well on most home set-ups.


Good luck, and let us know how it works for you.

 

[clonesix]

Upon reflection on the griddle, it might just be that too much heat escapes through the sides. If, perhaps you were to form a wall around the perimeter of the griddle, where the frame will rest on top, that may work for you/ It is worth trying before buying another heater.


WORD OF CAUTION: Fumes from heating plastic are toxic, and good ventilation is required. This has been a public service announcement.

 

[TJackFx]

WORD OF CAUTION: Fumes from heating plastic are toxic, and good ventilation is required. This has been a public service announcement.

This. Please do not heat your plastic with the same oven you cook food in.

 

[Duncanator]

Your seals (or lack there of) look to be the biggest culprit. You need to have a tight seal between the frame that holds you plastic and the platten (the perforated sucking surface). The air that the vacuum is sucking is going to follow the path of least resistance; so if there are any leaks, it won't pull the plastic down over the pattern.

Heating your plastic properly is important too. I don't use temperature as a guide to when the plastic is ready to pull (other than not burning it). I watch the way the plastic moves during the heating process to determine when it is ready.

Almost all plastics go through the same 3 states during heating:

- First: The plastic bows toward the heat source and then starts to wrinkle or get warpy. This is caused by differential heating as the heat soaks through the plastic from the heated side. and takes longer on thicker sheets of plastic. This stage sometimes looks like sagging but if you tap on the plastic, it is still somewhat hard on the surface.
- Second: The plastic pulls tight and smooth. This means the heat is mostly uniformly soaked in.
- Third: The plastic starts to sag. Now it is ready to pull. I usually let my plastic sag about half the thickness of my pattern (sometimes more, sometimes less). If you don't let it sag enough, it may cool before it pulls all the way onto your pattern. If it sags too much, you may get webbing (raised ribs on the sides of your part caused by the excess plastic folding in on itself). You'll have to experiment to get the right sag for the plastic and pattern combination you are using.

Hope this helps! Good luck!

 

[Grinn3r]

Thanks everyone for the detailed responses!
First off, the shopvac has a 3.5 horsepower. I'd tried looking all over the internet but no one specified the power of their vacuum so I assumed any old shopvac would do.
The griddle DOES heat, but not as well as it should... I've cranked it all the way up a couple times out of frustration to see what it'd do.
The thickness of the ABS is 1/16 inches and the Polycarbonate is .01 inches; both bought from Widget Works.
They heave some Styrene listed as well, would any of this work well enough? http://www.widgetworksunlimited.com/Styrene_Thermoform_Plastic_s/51.htm
The masks I'm making range in detail, from simpler ones like the old Hollywood Undead masks to things like Kindred from League of Legends.

I can probably cut down the platten I have to just smaller than the frame of the plastic if you all think that's what needs to be done. I still have plenty of leftover perforated board if I should just make a new one...

I think I still have the receipt for the griddle if I need to take it back. clonesix: I did have a similar idea in mind to build a foil lined box around the griddle to keep the heat in. Although I'm starting to get the feeling I should really get some of the other plastic to do this also.

I've heard a lot about not using the kitchen oven, but exactly what else does it do badly? (aside from the fumes)
And assuming that simply lining the bottom of my oven with foil and stacking the plastic on top of some wooden blocks over the bottom rack wouldn't work (a suggestion from my family), where would I find a good garage heater?

 

[clonesix]

http://www.amazon.com/Comfort-Zone-...555948&sr=8-2&keywords=Infrared+Garage+Heater

 

[Grinn3r]

It's been a little while since I last updated, but now I'm able to purchase the new materials I need to get set up properly.
Again, I appreciate everyone being so helpful to me.

- My local Home Depot has this vacuum for sale at a decent price, and it says it has a peak horsepower of 6. Would this one be sufficient?

- I'm going to try and do as Clonesix suggested and build a wall around the perimeter of my heat source for the frame to rest on top of, to see if it will work before I buy the heater they linked me instead.

- Also, I'm going to buy some styrene as well. From a different site though, due to WidgetWorks never responding to my emails. They send the products on time and have no qualms about taking my money, but it seems that customer satisfaction is none of their concern. :facepalm

I'll try and list any other updates as soon as possible. With the convention just three months away, and me having three costumes to work on, I'm not wanting to waste any time.

 

[cavx]

I still don't have my Vacuum former up and running where I can actually make stuff and the reason for that is (apart from lack of funds for the project) is that I keep discovering new and very interesting things. Some of them I will share here.

Vacuum cleaners (even shop vacs) don't pull more than 6"Hg.

MDF is often used in these boxes (platens), but my repeated tests have proven time and time again that MDF (raw) is porous and can only contain suction to 6"Hg. Basically it lets air through the medium density particles. A higher density board or a material like a hard plastic or metal works better. Sometimes, the heat from the plastic can pull the compounds that bond MDF out and this may leave a residue on the surface of the plastic. Metal is best for the platen.

If I take a piece of raw MDF and place it as the lid on my vacuum chamber, I can only pull 6"Hg.
If the MDF is laminated with raw sides, I can pull up to 10"Hg.
If the laminated board is sealed on the edges, 20"Hg is possible.

Seals must be 100% or as air escapes, cooler air cools the plastic as it rushes in to fill the void created by the suction.
You need soft rubber, not foam (I have seen examples where EVA was used) because like the MDF, foam is porous. I have not tested the exact limits here. Rubber does cost more, but lasts years.

Heaters must be able to heat between 130 degrees C and 250 degrees C depending on the plastic you are working. Thicker plastic requires loner heating times, not more heat. More heat may burn the surface.

Ideally you will test and create your self a LUT for all the plastic types you use with their heating temps and times.

A fan forced heater is the best idea I have seen and used so far. The heater in question is the lid off a "turbo cooker" or "easy cooker". The modern versions of these use halogen lights (instant heat) and a fan to force that hot air onto the plastic. These units used to cost several hundreds of dollars but now can be found as little as $40.

One of the better designed "ovens" I have seen uses an aluminium plate under the heater and the plastic is slid in and out from the side. This minimizes heat loss off the back off the sheet.

This is often shown as a cheap way to make things on You-Tube and no doubt, many have made this work. Many more have not, so hopefully the points above may help.

 

[Grinn3r]

I'm glad you've been doing your homework!
It sounds like you know a lot about this, and I'm thankful you're sharing.
While I'd love to have an optimum set-up as soon as possible, right now I'm just looking to get something that works well enough. ^^;
I'll definitely keep this in mind for future upgrades when I can.

I used caulk to hold my box together, won't that work alright for this?

And I talked to my grandpa earlier about my situation and he just went ahead and ordered the heater that was mentioned a few comments ago since it was recommended for this and we've seen a lot of people using them. So I think I'll at least be up to par on that area... maybe.

 

[cavx]

I'm glad you've been doing your homework!
It sounds like you know a lot about this, and I'm thankful you're sharing.
While I'd love to have an optimum set-up as soon as possible, right now I'm just looking to get something that works well enough. ^^;
I'll definitely keep this in mind for future upgrades when I can.

I used caulk to hold my box together, won't that work alright for this?

And I talked to my grandpa earlier about my situation and he just went ahead and ordered the heater that was mentioned a few comments ago since it was recommended for this and we've seen a lot of people using them. So I think I'll at least be up to par on that area... maybe.

I pretty much documented all my fails. My system did work (sort of) and why I didn't just give it up as a bad joke.

Silicones may or may not work. I know that without silicone, my lid on my vacuum chamber just seals on its own,where when I had silicone as part of the seal, I used to have to press hard on the lid to make seal to just start the suction. Pourable like a paintable or pour type molding silicones work a treat.

Right now, I am working on a female tool version vacuum forming.

Suction was as issue, but most of my issues was heating or losing heat whilst I got a good seal. The thing being, even with just a vacuum cleaner, once the seal was made, I could not lift the sheet of plastic off the platen. So with that in mind, I explored female tooling where you make a seal and suck the plastic into the tool, not over the tool.

Here are some test pulls using 3mm Perspex.

The beauty of this in a home workshop is that you don't need to work fast to make it work. You can make a seal when the plastic is cold and then heat the plastic. As soon as the plastic becomes pliable, it is pulled down into the tool. There is no upward expansion which can burn the sheets if your heater is located above as mine is.
Because I use a vacuum pump, not a vaccum cleaner, much quieter and I can lock off and turn the pump off whilst the plastic is heating.

My new rig will be able to do upto 700mm wide. It still needs seals and the MDF needs to be sealed as well. My tests are showing that liquid glass (epoxy) is a perfect sealant for MDF. I will have to make custom seals for both ends of the big pipe.

And some smaller test pulls

 

[Grinn3r]

That's pretty cool looking. The plastic looks great in your results, What did you use the domes for?

- - - Updated - - -

ALSO! The new heater came in just now. Thanks to clonesix for giving me the reccomendation and link.

 

[cavx]

That's pretty cool looking. The plastic looks great in your results, What did you use the domes for?

- - - Updated - - -

ALSO! The new heater came in just now. Thanks to clonesix for giving me the reccomendation and link.

I haven't used them for anything yet. Just needed proof of the concept.

Strip heaters are OK, but they do take time to get hot and I found the one I was using did not heat evenly. It started at one end and worked its way along and took ages to get hot right the way across. The other thing I noticed was heat differences between the strips. .

My redesigned heater unit now uses 4 x 500w halogens (Australia's power is 240V/50Hz). They will smoke softer plastics from as little 3 minutes. Soon I will add a fan to make it really hot. I made the lights pivot in so I can aim them into the centre. What I need is a nice thick aluminium plate to stop the heat passing through the plastic and dissipating into the air and make this a true "oven".