PVC molding
WHY BUY AN EXPENSIVE HAND BASIN FOR A CAMPER WHEN YOU CAN MAKE YOUR OWN?
Des shows us how to go about making a simple mold
If necessity is the mother of invention, then high costs are her offspring. So when Des Thomson got a quote for $900 for vacuum moulding a shower base for a camper van he was building — even though he had already made all the necessary moulds — he declined and ultimately did it himself for $50. And that included setting up the necessary workstation from which he could make anything else that caught his eye.
The result was a shower base that was not only as good as the one he avoided paying $900 for but also now reproducible for the equivalent of small change. And given that he is helping his local Menzshed build even more camper vans, he has saved a considerable amount of money in the long term.
That first campervan
Des’s foray into campers began with the twin-pull-out conversion of a Toyota van, for which he manufactured two fibreglass telescope-like pods that extended 1.8m beyond the back door — a project which featured in Issue No. 76 of The Shed in January 2018.
He already had an interest in casting and had made several aluminium components for use in other projects. This meant that vacuum moulding was just a variation on a familiar theme, with the principles of one being much the same for them all. And like any such practice, the quality of the final result isn’t determined by the expense or precision of the equipment; rather it is the quality and attention to detail that go into making the initial moulds, in this case a small hand basin for campers.
Des and the workstation
Making moulds
The moulds themselves can be made from whatever scrap there is available.
Ply and MDF glued together in layers is the most suitable, due to their stability and ease of cutting and shaping them. If you have timber that is sufficiently dry, that is also suitable, especially if you are trying to reproduce a damaged timber moulding with a complex profile. The downside to working with MDF is dust, so diligence in forming and shaping includes dust control and wearing a dust mask. In the case of ply, any imperfections in the edges can be filled. For a female mould, these issues will be of little consequence, as any defects will be hidden on the underside of the component. But more about that shortly.
There are several aspects to this process: the shape to be formed, the frame that holds the material — in this case thermoplastic — in relation to the mould to complete the process, the frame that holds the mould itself if it is a female mould, and the workstation and vacuum table that is central to the whole process.
Taking care will pay off
While the mould is specific to the job at hand, each of these other items can be used many times over. In the case of the mould, it can be used to make any number of components, particularly if you take care preparing it.
Any error or flaws will show up each time — a bit like copying and pasting a mistake.
The forming of the moulds is the most time-consuming task (the hand basin took about a day) while the actual vacuum-forming process itself is very quick. Like a lot of similar procedures, the quality of the work is largely determined by the quality of the preparation, however the final forming operation requires diligence and supervision: it is easy to make a minor mistake that will cause the final component to fail.
What is interesting is that failure does not automatically write off the thermoplastic being used. Put it back through the same process, and there’s a good chance that the original flat form will be restored and the material made fit for reuse.
Male or female mould?
The decision as to whether a male or female mould is required depends on the nature of the project and the material used.
The moulds themselves can be made from whatever scrap there is available
Des used acrylonitrile butadiene styrene (ABS), a thermoplastic polymer that is commonly used to line showers. In this case he bought a piece of 2mm thick off-cut shower liner from a local plastic supplier, which he then cut down with tin snips.
Shower liner is interesting in that it consists of two layers: a very thin layer of acrylic, and a thicker backing of ABS. The ABS provides the strength and the acrylic the final glossy surface. You’ll see shortly that knowing this thickness is an important part of the process. The ABS side should always be up, producing a finished surface that is glossy and free from imperfections. This is why Des chose to use a female mould, as the ABS was to be pulled down into the mould to form the final shape.
In the case of a composting toilet he also built for the camper, he used a male mould, as the ABS was to be draped over it to form the shape as well as achieve the same level of finish.
The ABS provides the strength and the acrylic the final glossy surface
Moving to the next stage
Once the moulds are formed, any holes or imperfections can be filled with Plasti-Bond or Polyfilla, taking care to ensure that they have cured completely.
This can vary depending on temperature and humidity, so don’t be in a rush to move on to the next stage, which is to seal it with whatever paint you might have at hand, in this case a waterbased undercoat. The next step, once you’re satisfied with the final product, is to prepare the mould for the vacuum process. In the case of a female
The final forming operation requires diligence and supervision
mould, a grid of small holes is drilled at approximately 20mm apart in both directions, with their diameter being half that of the thickness of the material being used. Any more and they become obvious in the final form, while any less and they aren’t sufficiently effective.
It is through these that the process brings together the mould and the material being used. In the case of a male mould, large, well-placed holes are sufficient, as they aren’t part of the final outcome.
Making the frames reusable
The frame that holds the piece of ABS in position is the next item to be made, and again the emphasis is on getting it right to ensure that it can be reused.
These frames are made from scrap 30x20mm wood, hinges and
over-centre catches to hold it together, and a self-adhesive door-draught seal to ensure the integrity of the vacuum. Des dowelled and butted the corners rather than using a mitre, which is a good indication of the forces and stresses achieved once the process begins, along with contributing to the frame’s longevity.
The second frame — the one that holds the mould — is constructed next, in much the same way as the first, in this case from 18mm ply. The door draught seal adheres to this, so the accuracy of these two faces in relation to each other is very important. If the vacuum can’t form, the process stops before it begins, and this is the point at which it is most likely to happen.
Des’s workstation
The actual process is simple and straight-forward. After several trips to the Eco Store — the Christchurch City Council’s retail store for items salvaged from its land-fill depots — Des built a simple but effective vacuum press.
The vacuum-mould workstation was built on an old trolley from the long-term care hospital which the Halswell Menzshed is attached to. The completed workstation consists of two vacuum cleaners, two radiant three-bar electric heaters reorganized into a folded Zincalume chassis, independent switches for both the heaters and vacuum cleaners, a vacuum frame using PVC connectors to make a manifold, and a basic wooden frame to hold it all together.
If you’re uncertain about the electrical considerations, find someone with professional electrical knowledge who can give it the once over. In the case of this workstation, the trolley is steel, so a shorting could have severe consequences.
A point to be made here is that while both heating elements and electrical circuitry are required, there is no risk of fire or damage. The whole operation is over in a few minutes and requires total supervision and interaction. The temperature of the heating elements is typical of any radiant heater, so you would treat them the same way you would any other heater.
Creating a good vacuum
Des runs his vacuum cleaners without the filters and bags to get the best
Des watches until the ABS is free-formed with no wrinkles or stresses
result; he is after all only using them to create a vacuum. These are in turn connected to a vacuum table made from two sheets of 18mm MDF separated by a 20mm spacer all around, ensuring a consistent vacuum across the underside of the table.
A home-made manifold using PVC jointers connects the cleaners to the table. The use of the two cleaners doesn’t increase the strength of the vacuum, only the speed at which it happens. For anyone familiar with this process, the final pressure is around seven inches of mercury (inHg) (178mmHg), as opposed to commercial systems that operate around 23–27inHg (584–686mmHg).
The top of the 600x600mm table is drilled with 5mm holes at a grid of 50mm. How much of that needs to be used depends on the size of the project, with a small one such as these hand basins allowing for much of the area to be blocked off with plastic and tape.
This reduction ensures the concentration of the vacuum where it is needed.
A quick process
The temperature for the process is surprisingly low, and Des keeps an eye on it with a hand-held digital thermometer. He tests much of the process by touch before starting, while looking for consistent ‘droop’ across the underside of the suspended ABS. Having mounted the frame with the ABS above the positioned and sealed mould, Des watches until the ABS is free-formed with no wrinkles or stresses, at which point it is ready to be applied. It is then lowered quickly and accurately over the mould, turning on the vacuum cleaners at the same time. Speed and precision are required, as the process takes only seconds, so it might pay to practise a few times if this is your first attempt at vacuum moulding.
And that is it. The final product reflects the work and detail, so the better the preparation, the better the outcome.
What if you do get it wrong and make a mess of it? Just do it again, with the same piece of ABS. Reheat it in the frame until it flattens out, then repeat the process, making sure that you address the mistake you made on the first attempt.
Endless possibilities
This is a fun project for any sheddie. The cost is low, the skill level required is moderate, and the finish will be ‘just like a bought one’ if you’ve been conscientious throughout.
From here on, you can figure out how to make a range of moulds. Just don’t get caught using the expensive household vacuum cleaner, or else the concepts of male and female moulds might take on a whole new meaning.