Vacuum Forming for Free

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Introduction: Vacuum Forming for Free

I build props. I've built props for theatre, including Broadway, off-Broadway, off-off-Broadway, ...

I recently needed 12 fake candlestick phones for a musical ("Crazy For You"). Real candlestick phones are incredibly expensive, and even replicas were too much for my budget. All 12 needed to match as well. I decided to make them all.

I wanted to match the shape of the bases to the real thing, but it would take too long to sculpt 12 bases, and casting them would be too expensive. It looked like it could be vacuum formed. I've worked with plastics in the past, but never with a vacuum former, though I've seen some in action. I couldn't spend a lot of time or money building a vacuum forming machine for this project; I figured if I liked what it was capable of, I would build a nicer one after this project based on what I learned.

After researching what I needed, I found I could build one for free. I already had the necessary components in my shop. I figured many prop makers will already have these parts as well, so I am sharing how I did it.

Step 1: Gather Your Materials and Tools

For me, this vacuum forming machine was free, but that's because I already had all the tools and materials. These include:
* a shop-vac
* a heat gun
* some scraps of MDF
* some scraps of lauan
* spring clamps
The tools I used were a drill press, a table saw and a small hand saw, a combination square and a pencil. I also used a bit of glue and some grid paper. 
You can substitute some of the tools used as well as the precise materials needed. The shop-vac I had cost $25 new, and the heat gun was $25 new as well, both from the big-box hardware store. So if you had to buy everything for this, it would only be $50 for the equipment and a couple bucks for the materials. Even if you never vacuum form again, you can still use the shop-vac for cleaning your shop and the heat gun for other projects.
The plastic I was using was a thin sheet of Sintra, which is a brand of expanded PVC. It was about 2-3 mm thick, and I cut it into smaller squares using a utility knife and a straightedge. 

Step 2: The Top of the Platen

For the top of the platen, I cut a square of 1/2" MDF to 8 inches by 8 inches. You can make it bigger or smaller if you want; I made mine as small as possible for the pieces I was making. That way, I would not have to use a giant sheet of plastic for each item. I used MDF because it gave me a nice smooth and level surface for the top, which is an advantage in vacuum forming. You can substitute other materials, such as 3/4" MDF or even a piece of melamine board. You do want to be careful about using painted or coated pieces, as the heat of the plastic may melt or burn these.
I drilled a grid of holes through the MDF. I taped a piece of grid paper to the top to make the layout easy. I used a 1/8" drill bit; you do not want the holes to be too big. I left an inch undrilled around the border; this is where the frame will sit.

Step 3:

I ripped some 1/4" MDF strips to 1 inch wide and glued them along the perimeter of the bottom of the platen. Make sure to fit these tightly together so no air can escape through the joints.
I then drilled a large hole with a spade bit in another 8" by 8" square of 1/2" MDF. This hole was just large enough so I could shove the end of my vacuum hose in and it would stay in place. I attached this MDF square to the other side of the 1/4" strips, making a "sandwich". The empty cavity in the middle of the sandwich allowed air to be sucked into each of the tiny holes when the vacuum cleaner was turned on.

Step 4: The Frame

The plastic itself needs to be held in a frame. I used two pieces of 3/16" lauan with a 6 inch square cut out of the middle. The plastic would go between these two frames and everything would be clamped together (making another "sandwich" of plastic with two pieces of lauan "bread").
I actually plunge-cut the inner squares on my table saw and finished the cuts with a small hand saw. You can use a jig saw or whatever other tool you feel more comfortable using.

Step 5: Testing

I was ready for my first test. I grabbed some random objects and arranged them on the platen.
I was using some Sintra plastic (expanded PVC) for my vacuum forming I had left over from a few years ago. I think it's about 2-3mm thick. I clamped it inside the frame and heated it up with my heat gun for a few minutes until the whole piece was very flexible. (While writing this Instructable, I also learned that Sintra can be softened by submerging it in boiling water for 10 to 15 seconds, which seems like it would heat it more evenly).
When the Sintra is fully heated, turn on the vacuum cleaner and place the plastic over your objects onto the platen. The plastic will stretch as it lays over the objects; when the frame touches the platen and creates a seal, the vacuum will be able to suck the plastic tightly over the pieces. Make sure to bring the frame straight down rather than from the side, or you may stretch parts of the plastic and cause it to tear.
I found if the plastic does not pull as tightly over some parts as you would like (either because the plastic was not heated enough in that spot, or because the vacuum is not strong enough), you can heat it up some more with the heat gun as the vacuum is still running. With plastic as thin as I was using, it was really easy to burn holes through the plastic if I heated up a spot for just a split second too long.

Step 6: My First "pulls"

The model for the phone base itself was built up out of a few layers of MDF and plywood. I used Bondo (a thick type of polyester resin used for auto body filling) to smooth and refine the surface. In bigger and more powerful vacuum forming machines, you want to make sure to build your models out of something strong and solid because materials like Styrofoam can be crushed under the pressure. For a machine this small and weak, that probably won't happen. You should also avoid materials that will melt or deform under heat.

I wanted a clean edge along the bottom; I raised the model up a bit so the plastic would be pulled underneath it a little bit. I used 3 tiny pieces of MDF to hold the model up without covering any of the air holes.

The model I built was just a bit too big for this vacuum forming machine. If I were to do this again, I would make the platen 2 or 3 inches bigger on each side.

A vacuum cleaner is a really weak source of vacuum. If I were upgrading this machine, that is the first thing I would replace. I found that after I placed the plastic over the mold, I could use the heat gun to heat the spots which did not get sucked down all the way, so I was still able to get all 12 pieces out of this machine.

Step 7:

Here is a photograph showing a phone in progress so you can see more clearly what I was doing.

I also made a video which goes through the construction of this machine as well as letting you see it in action.



Vacuum forming is a great method for creating many types of props and costume accessories. If you have never tried it but are curious about what you can do, I hope my free method will help you get started.

Step 8:

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56 Discussions

great, will try it some time!

UPDATE: I checked out my local plastics supplier today to get some more plastic to finish these phones. It turns out what I was using was NOT Sintra, but styrene. I was using .030" styrene, and all they had was .040" sheets, so that is what I got. I hope it is not too thick to use on my machine, but I only have 4 more to pull.

2 replies

What a great Instructable. I too occasional built props as well as doing scenic design and construction for schools and local community theaters. I've always been fascinated with vacuforms. I will archive your instructable for future reference.

Years ago, while searching props on the web, I came across a website that offered instructions for building an actual vacuform table, complete with heating coils and a hinged frame for moving the heated plastic from the heat bed over to to the platen/vacuum bed. It was build to one of the plastic industry's standard sheet size (I believe about 48"X60"). Sadly, by the time I was in a position to build one, I could no longer find the website.

I was also in need of candlestick phones, years ago, for a production of "Cabaret", and I ended up building them out of parts cannibalized from thrift store table lamps. I wish I'd had your instructable then.

Well done. Keep up the good work!

TheStarWizard

PS
If anyone comes across instructions for building a large vacuform table that doesn't require putting the plastic in your stove's oven, please let me know. Thanks!

I know this was four years ago that you asked for stoveless-vacuforming table but I came across this vacuform tutorial and thought perhaps even if you no longer needed such a thing someone else might benefit from the link:

http://www.tk560.com/vactable4.html

I did some vacuum forming several years ago. I user an old screen printing frame. I used pegboard an a floor vacuum. I used the methods discussed except I put the plastic in the hinged part of the frame. With the frame open (like a book) I heated the plastic with a heat lamp. When the plastic sagged, I turned the vacuum an closed the frame (again like a book) I don't rember what I was doing, but it turned out ok. It's been fun reading this forum.

Mcwllt1

this is very interesting ible and also some good food for thoughts....thanks for sharing. I will try for some experiments. I own a vacuum of Philips that reaches about 8 BAR (That it says the label) (philips triathlon model). this plastic for molding has any special feature and comes with various thickness? how thick is yours....



thanks

2 replies

8 BAR? If one could achieve a perfect vacuum, this would amount to slightly over one BAR or about 30 inches pressure. This barometric pressure is often seen on Tee Vee when the weather is announced. A vacuum pump could never "pull" more than this because the air pressure of our atmosphere that is actually doing the pushing hardly goes above one BAR. Standard atmospheric barometric pressure is given around 1013 millibars, or 1.013 BAR.

As another example, If a person 50 ft above a jar of water sucks a "perfect" vacuum using a 50 ft straw, the highest the water will go up the straw is about 34 feet (at sea level). Any water column taller than 34 feet would weigh more than the weight of the atmosphere (14.7 lbs/sq in) that is pushing the water upward. Imagining a one inch by one inch square tube filled up to 34 feet will weigh about 14.7 pounds if one uses the weight of water (about 62.4 lbs/cubic foot). A simple calculator works wonders here.

This info is not necessary for the project here but the info revealed here might be interesting to some...

The plastic I was using was .030" thick. It has no special features other than it has to be a thermoplastic (one which becomes flexible when heated and rigid when cooled back to room temperature). Styrene is one of the cheaper types, making it popular with prop makers doing vacuum forming. Others include PVC (vinyl), Kydex (a brand name for an acrylic/PVC copolymer), ABS, CAB, and acrylic (plexiglass). You can also use PET and polyethylene, which you can get from soft drink and milk bottles, but these are extremely difficult to paint or glue to.

Fantastic! Every prop maker is always trying to find new ways to get stuff done. This is a great bit of info! Thanks for sharing!

This is an interesting instructables about DIY vacuum forming. You really have a good feel on this topic, and the way you wrote about it made it both interesting to read, and informative at the same time. Thanks a lot for sharing. Vacuum Forming UK

I'm a little late in posting but modifying the reed valves on a small cheap automotive compressor might do the trick for producing a strong vacuum.I have seen a very small unit on a job site used to align two pieces of granite together for counter-tops,and it was no larger than a 12v air compressor to fill your tires .I repair my own compressors and found they use reed valves to maintain constant psi.why not reverse the process for vacuum,. it might require some mod.like an added check valve.I'm curious if anyone has tried it yet.

I love it as a get started cheap method.
like you said if you find you want more better capability then you can justify spending more money and time to build a better one.

so i take it that more heat and a more powerfull vac would make this alot better? i have a 16 gallon wet / dry vac and a good heat gun, what is the max size plate i can use?

2 replies

A more powerful vac would make it better, but from what I've read, a larger shop vac is not more powerful than a smaller shop vac. Larger and more powerful shop vacs move more air in less time than smaller ones, but the amount of vacuum pressure is still between 2 and 6 inches of Mercury.

Also, while a heat gun is usable on smaller pieces like I was doing, when you start getting bigger, you want more of an even heat, like with an oven. Even with a powerful heat gun, you'll end up heating one section until it is pliable enough for forming, and when you move to heat up another section, that first section will cool back down. I had a thought of building a small "hot box" to hold my plastic while I heat it (maybe just an enclosed box lined with aluminum foil) so the heat will not dissipate so quickly as I use my hot air gun. Still, my next step would be to build a better heating system because using a hot air gun really limits the size and thickness of plastic you can use.

Good thoughts Eric. I can see the vac thing as you say,. I have the big shop vac and a smaller (9 gallon) ridgid shop vac and i tend to like the smaller one more..I never even thought to see which one has more suction.

A Hot box..thats an idea. like you say, build it, line it with something shiny like tin foil, use that tin foil tape to close all the seams then, build a bigger version so you can insulate the smaller one, put the bigger one over it so you shouldnt lose any heat. You would probably need one heat gun on each end though. I wanna try this and see what I can make....lol

Very nice, Eric!

This may be enough incentive for me to buy a vacuum pump. Or, who knows, maybe make a a multi-stage shop vac? Maybe a high speed drive on my old shop vac parts? OK, I'll start slow, use the one I've got.
Then I will have to think of something to vacuum form.

Excellent video.

Cool project indeed - from your experience can we use the PET bottle material? Do you think hair drier would give enough heat to soften this material?