Building Vacuum Forming

7/29/2019 Building Vacuum Forming

1/13

Building Your Own Vacuum Forming Jig

by Rogerio "Rato" Marczak

This is all you need to make your first vacuum forming jig.

START WITH A SMALL ONE

Vacuum forming is one of the oldest techniques in plastic industry, and it has found its way inmany modeling branches. Everyone remembers ID Models and Rareplanes kits from the past.It still is the only game in town in many cases, particularly for large scale subjects which are

not comercially viable for mainstream manufacturers.

The other side of the coin is that vacuum forming is a cheap, yet extremely valuable methodto produce many kinds of parts at home. Yes, you need a master (mold), but almosteverything can be used to make a master for vacuum forming: plaster, car filler, wallputty, resin, balsa wood, and even injected kit parts. And of course, a vacuum cleaner is alsorequired. It will provide the suction necessary to conform a heated plastic sheet over the mold.So, the word vacuum is somewhat misused here, but thats another story...

I wont describe the method here, since most of you are familiar with the technique. Keep inmind, however, that the nature of the process doesnt allow you to reproduce tiny details. Theidea is to create the part with its correct dimensions and shape - a shell on which smaller

details can be added later. A short description of the technique can be found in many internetsites (here, for instance)

In this article I will show you how to built your own vacuum forming table. It is a small one,aimed for making large scale canopies and small parts like landing gear doors, rudders,external fuel tanks etc. The principle is the same for jigs of any size, though, so if you want alarger one just upscale everything here. Thats the way master modelers go to make theirlarge scale fuselages and wings.


2/13

And yes, there are a few comercially available vacuum forming tables aimed for the modeler.Warmplastic for instance sells a very popular table in several sizes. If you dont havemodeling budget constraints, stop reading now and go for it.

A SIMPLE BOX

The first step is to build a strong box. The purpose of the box is twofold: it creates an emptyspace which equalizes the pressure under the plastic sheet being formed and provide enoughroom to attach the vacuum cleaner piping. I built mine from wood and nails, but I heard ofpeople using those plastic items used to make electrical switch boxes. You can also findready made wooden boxes in craft shops.


3/13

Box construction.

The sketch above gives you an idea of the assembly. I used 1 cm thick wood boards. Thefinal dimensions of this box is approximately 15 x 10 cm and 6 cm high. Note that you have toopen a hole in one of the walls to install the connection to the vacuum cleaner. The diameterof this hole is determined by the diameter of your vacuum cleaner hose. Make it slightly

oversized. Once finished, I applied a coat of wall filler all around and sanded flush for a betterappearance. On the inner side, I brushed a heavy coat of enamel to seal the internal walljoints (sorry, I forgot the FS number...).

The wooden box puttied, sanded, and painted on the inside.

I decide to build my own box because I wanted a small step along the upper border to providebetter support to the mesh that will be installed at the top. I failed to find something like thatready made...


4/13

Note the step along the border to provide support to the mesh.

I used a comercial vacuum cleaner accessory to make the hose connection. Because of its conical shape, it isjust a matter of pressing it firmly to the perforated wall. The friction will provide a snug assembly. If you cant finda similar item, a piece of PVC piping wil do the job.

Hose connection.


5/13

The connection installed in the box.

THE GRILLE

I started by the simplest grille: a thick acrylic plate with 2 mm holes spaced by 1 cm in bothdirections. Smaller distances would be better, but the task would be increased by powers of2!!! Instead, I decided to install a steel mesh on top of the acrylic plate. Much better: the meshwill distribute the suction evenly all over the area, even if you made just a few holes in theacrylic plate (and now we know why that strange textures on the base of the Falconcanopies...it is the negative form of the mesh).

The perforated plate will rest on that small step left along the upper border of the box, someasure carefully the inner dimensions of the box before cutting. The mesh goes on the topof the plate. Since both (the acrylic plate and the steel mesh) were cut slightly undersized, Ibuilt an armature of brass rods soldered in the corners to be used as a clamp atop everything.Try to make the dimensions of the armature as close as possible to the box opening. This willeliminate the need to seal the joints afterwards.


6/13

The components of the grille.

Next, I glued the armature/mesh/plate sandwich with epoxy glue. This is not strictlynecessary, but now the grille can be handled as a single piece.

Assembling the grille components.

Now you can test fit everything. Luckly, my grille fitted very tightly, avoiding further touch-ups.


7/13

Our vacuum forming jig is virtually done:

Test fitting the components.


8/13

Dont worry if your seams are not tight. You can seal them in the end.

FINISHING

Well, since we have gone this far, what about a bit of aesthetics? I took a wide flat brush andapplied a heavy coat of gloss black enamel around the outer surfaces. The jig looks much

better now.


9/13

The box already painted.

Next, I decided to add some grip to the base of the box (remember, you will probably use thatgreasy kitchen table). I screwed three rubber shoes to the bottom of the box. I used three ofthem because three points form a plan. Had I used four, the box would swing slightly and...Ok, ok, I used three because I had only three of those rubber shoes.

My anti-slip device.

Now the grille can be permanently installed. If i t doesnt fit snugly to the box, fill up the ridges


10/13

with silicon gel, white glue or epoxy glue.

Eliminating air scapes.

And thats it. The harder part has gone and we are almost there. Take a look:

The finished box.

CLAMPING FRAME

The clamping frame is part of the project. Without it, the box is not of much use. I made minefrom 3 mm hard wood boards. It is necessary to make two of these, with the same opening inthe center. The plastic sheet to be formed will be sandwiched between them. It is important to


11/13

use a heat resistant material (remember, the clamping frames, with the sheet in between, willbe heated in the oven to soften the plastic sheet). So, my choice of wood possibly was not thebest choice for a long term usage. Anyway, it is easier to build than metal. In addition, thewood grain will act as a grip to avoid the plastic sheet slipping between the frames during theforming. Ive seen frames made from metal and they generally require bolted joints to hold theplastic sheet properly. After making dozens of parts, Ive never faced slipping problems with

my wood clamps (so far, at least). On the other hand, repetitive exposure to heat can warpseverely frames made from bad quality wood.

The sketch below shows the two sets I made for the box described. The version with thelarger opening uses all the working area of the grille, while the one with a smaller opening isused for smaller parts like spinners, landing gear doors, wheels and 1/72 canopies. It saves alot of styrene...

The clamping frames (dimensions in cm).

Because I didnt use any bolted connections in this design, I simply employ office clamps toprovide the fixture of the styrene sheet.


12/13

Holding the plastic sheet in the frame.AND FINALLY...

And finally we have our own vacuum forming table. Take a look:

The finished jig.

Of course it has its faults. In retrospect, I should use some sort of tabs on the lower clampingframe to make alignment easier. When you remove the frame from the oven, you must move

fast to avoid excessive cooling of the sheet.

As I mentioned before, Ive been using this device for almost two years. Everytime I failed toproduce an acceptable part it was due to incorrect heating of the sheet or misalignment of the

clamping frames with the box. My fault in both cases. Another important factor that Idiscovered by the hard way: it is not your vacuum cleaner which is weak, it is you that didnt


13/13

remove the dust filter from it (you will be amazed how this simple action increases the powerof your old vacuum cleaner).

As a last note, remember that you can also build an adapter to increase the working area ofyour jig. It is basically another box (equiped with a larger grille) that fits this small one. Of

course in this case you will need new clamping frames too.

You may argue that this is a lot of work for something that is comercially available. Well, themoney is yours. And besides, this can be a good entertainment for a rainy weekend between

two model projects. It is very easy to build (Im no carpenter) and a must have item for thescratchbuilder. I didnt showed the device in action because another article showing its use is

in my to do list, and will follow shortly.

Documents

Building Vacuum Forming