General Lee’s vacuform how to guide
After getting hold of a stompa kit I decided it needed a head swap to match my scratch built gargant and nowhere could I find an appropriate piece to make do. After a lot of research I stumbled on vacuforming. This is a process where hot plastic is dragged over a form using a vacuum to leave an impression. You probably have examples of vacuforming lying around your workbench. Its how blister packs are made. I’ve put together this how to guide in case you are interested in giving it a try yourself
Part one- Building a vacuform table
The first thing you need to do is assemble materials. For mine I used a pine box from B&Q substantially cut down but you can make the box yourself.
Box, (400mm x 300mm x 50mm)
MDF sheet (400 x 300 x 12) for the top
MDF sheet (340 x 225 x 12)x 2 for clamp
Gaffa (duct) tape
3mm drill bit
A domestic vacuum cleaner with a hose
Vacuum hose connection (this may take some searching!)
Some way to cut a hole in the base of your box to fit the vacuum hose connection*
4 bolts with butterfly nuts
Drill bit to match bolt diameter
Countersink drill bit
I started by cutting down my box to 50mm deep with a circular saw. Then I cut a hole in the bottom of the box to fit my vacuum connection. For my vacuum connection I was lucky enough to have a dust extractor connection from a power sander but if you don’t have such a thing a short length of PVC pipe that fits snugly over your hover pipe will do. Cut a hole in the base of your box so that this fits tightly. I used a milling drill bit but a hole saw of the right diameter would be easier
I then made my clamp frame for holding the plastic as it melts by taking the 2 sheets of MDF and screwing them together in each corner about 10mm in from each side. I then used a jigsaw to cut a rectangle 280170 out of the centre. I then removed the screws and drilled holes for the bolts and countersunk them. If the bolt heads are not flush with the base of the clamp you will not get a good seal and vacuum will not work.
Once I had made the clamp I centred it on the larger MDF sheet and marked the inside and out. Putting the clamp to one side I then marked out a 1” square grid. Then I marked out a second offset 1” square grid so that the lines cross in the centre of each square from the previous grid (see illustration). Using the 3mm drill bit I then drilled out each intersection. Doing this allows for even airflow around the form and a better pull.
I installed the hose connection then sealed every joint inside and out on the box including around the hose connection using silicone sealant Next glue the top onto the box with wood glue and seal the joints once the glue has set.
To ensure no vacuum leaks I then gaffa taped all the joints
You should now have a vacuform table ready to test.
Part 2 using the vacuform - set up
Take a sheet of plasticard between 20 thou and 60 thou 0.5mm-1.5mm and secure it in your clamp. With the position of the bolts you will need to drill out holes for the bolts to go through. A craft knife with a no 11 blade will do fine rather than getting the drill out again. If you are using white plasticard, hold it against the clamp without the bolts in then hold it up to the light and mark the holes. For black plasticard put the clamp frame over it and mark the centres with pencil. Don’t make the holes too big otherwise it will weaken the corners.
Once the plasticard is mounted in the clamp frame and the frame is securely bolted together, head into the kitchen. Set up your vacuform table and attach your vacuum cleaner close to your oven so there are no hoses or cables between the oven and table. You will be quickly transferring very hot plastic between them so keep trip hazards to a minimum. Make sure your vacuform table is stable too.
Place spacers in the oven so your clamp is raised above the oven shelf. I use empty baby food jars but upturned small glasses or blocks of metal would work so long as they will withstand the temperature.
Pre heat your oven to 160 C gas mark 3
Part 3 forms
You can use anything for the form provided it will withstand 1 atmosphere of pressure and resist 160 C for about 40 seconds. Do not use your vacuform to replicate copyrighted material. Sculptors work long and hard to make the masters.
I’ve found balsa works well for forms. Most model shops sell it. It is easy to carve and takes the pressure. I tried Sculpey, an oven bake clay but this cracked under the pressure. I will try it again with a smaller solid piece as the piece I used was based round a tin foil armature and pretty thin. Avoid using forms that are too deep otherwise you will get webbing where pleats of plastic don’t suck close to the form
Once you have a suitable form position it on your vacuform table so there is plenty of space around it. Too close to the edge or other pieces will lead to poor impressions.
Raise the form off the table with spacers. I use one or two pennies in a stack in several places under the form. This allows an even airflow around the form helping to get a good pull.
Part 4 hot sucking action!
Put your clamped plasticard in your pre-heated oven for a little bit. If you have a glass door keep an eye on it. You will see it sag in the middle and then straighten again. At this point it is ready, you will also be able to tell when it is ready by the distinctive smell of melting plasticard. Switch on your vacuum cleaner and put your oven gloves on. Carefully but quickly take your clamp out of the oven and transfer it to the table. Position it so it covers all of the holes in the table and stretch it down over the form. Push the clamp down so it forms a seal. Hey presto, vacuform! The air is sucked out from in between the flexible plasticard and the table leaving an impression of your form. Let the vacuum cleaner run for another 20 seconds or so, so the plasticard starts to set in its new shape. Turn off your vacuum cleaner and oven and leave the plasticard to cool for 5 minutes. The temptation to take it out of the clamp now is very strong but the bolts will still be hot and the plasticard warm. Once everything has cooled down remove the form that may have got stuck in the plasticard and take the plasticard out of the clamp.