Your Own Vacuum Forming Jig
Rogerio "Rato" Marczak
This is all you need to make your first vacuum
WITH A SMALL ONE
Vacuum forming is
one of the oldest techniques in plastic industry, and it has
found its way in many 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
method to produce many kinds of parts at home. Yes, you need
a master (mold), but almost everything can be used to make a
master for vacuum forming: plaster, car filler, wall putty, resin,
balsa wood, and even injected kit parts. And of course, a vacuum
cleaner is also required. It will provide the suction necessary
to conform a heated plastic sheet over the mold. So, the word
vacuum is somewhat misused here, but that´s another story...
describe the method here, since most of you are familiar with
the technique. Keep in mind, however, that the nature of the
process doesn´t allow you to reproduce tiny details. The
idea 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 internet
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 a larger one just upscale everything here. That´s
the way master modelers go to make their large scale fuselages
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 don´t have modeling 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 empty
space which equalizes the pressure under the plastic sheet being
formed and provide enough room to attach the vacuum cleaner
piping. I built mine from wood and nails, but I heard of people
using those plastic items used to make electrical switch boxes.
You can also find ready made wooden boxes in craft shops.
The sketch above gives you an idea
of the assembly. I used 1 cm thick wood boards. The final
dimensions of this box is approximately 15 x 10 cm and 6 cm
high. Note that you have to open a hole in one of the walls
to install the connection to the vacuum cleaner. The diameter
of 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 better appearance. On the inner side, I brushed a heavy
coat of enamel to seal the internal wall joints (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 provide better support to the mesh that will be installed
at the top. I failed to find something like that ready made...
I used a comercial vacuum cleaner accessory to make the
hose connection. Because of its conical shape, it is just a
matter of pressing it firmly to the perforated wall. The friction
will provide a snug assembly. If you can´t find a similar
item, a piece of PVC piping wil do the job.
Note the step along the border to provide support
to the mesh.
The connection installed in the box.
I started by the
simplest grille: a thick acrylic plate with 2 mm holes spaced
by 1 cm in both directions. Smaller distances would be better,
but the task would be increased by powers of 2!!! Instead, I
decided to install a steel mesh on top of the acrylic plate.
Much better: the mesh will distribute the suction evenly all
over the area, even if you made just a few holes in the acrylic
plate (and now we know why that strange textures on the base
of the Falcon canopies...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, so measure carefully the inner
dimensions of the box before cutting. The mesh goes on the top
of the plate. Since both (the acrylic plate and the steel mesh)
were cut slightly undersized, I built 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 will eliminate the need to seal the
The components of the grille.
Next, I glued the
armature/mesh/plate sandwich with epoxy glue. This is not strictly
necessary, 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. Our vacuum forming jig is virtually done:
Test fitting the components.
Don´t worry if your seams are not tight. You can seal
them in the end.
Well, since we have
gone this far, what about a bit of aesthetics? I took a wide
flat brush and applied a heavy coat of gloss black enamel around
the outer surfaces. The jig looks much better now.
The box already painted.
Next, I decided to
add some grip to the base of the box (remember, you will probably
use that greasy kitchen table). I screwed three rubber shoes
to the bottom of the box. I used three of them 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
My anti-slip device.
Now the grille can be permanently installed.
If it doesn´t fit snugly to the box, fill up the ridges
with silicon gel, white glue or epoxy glue.
Eliminating air scapes.
that´s 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 mine from 3 mm hard wood boards. It is necessary to make
two of these, with the same opening in the center. The plastic
sheet to be formed will be sandwiched between them. It is important
to use a heat resistant material (remember, the clamping frames,
with the sheet in between, will be heated in the oven to soften
the plastic sheet). So, my choice of wood possibly was not the
best choice for a long term usage. Anyway, it is easier to build
than metal. In addition, the wood grain will act as a grip to
avoid the plastic sheet slipping between the frames during the
forming. I´ve seen frames made from metal and they generally
require bolted joints to hold the plastic sheet properly. After
making dozens of parts, I´ve never faced slipping problems
with my wood clamps (so far, at least). On the other hand, repetitive
exposure to heat can warp severely frames made from bad quality
The sketch below
shows the two sets I made for the box described. The version
with the larger opening uses all the working area of the grille,
while the one with a smaller opening is used for smaller parts
like spinners, landing gear doors, wheels and 1/72 canopies.
It saves a lot of styrene...
The clamping frames (dimensions in cm).
Because I didn´t
use any bolted connections in this design, I simply employ
office clamps to provide the fixture of the styrene sheet.
Holding the plastic sheet in the frame.
| AND FINALLY...
And finally we have our own vacuum
forming table. Take a look:
The finished jig.
it has its faults. In retrospect, I should use some
sort of tabs on the lower clamping frame 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, I´ve been using this
device for almost two years. Everytime I failed to
produce 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 I discovered by the hard way:
it is not your vacuum cleaner which is weak, it is
you that didn´t remove the dust filter from
it (you will be amazed how this simple action increases
the power of your old vacuum cleaner).
As a last note, remember that you can also build an
adapter to increase the working area of your 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, the money is
yours. And besides, this can be a good entertainment
for a rainy weekend between two model projects. It
is very easy to build (I´m no carpenter) and
a must have item for the scratchbuilder. I
didn´t showed the device in action because another
article showing its use is in my to do list, and will
I hope you find this article useful.