One of the most friendly building materials to use is polystyreen plastic card and strips. You can spent a fortune buying expensive packages with a few strips, so in practice I normally cut these from sheet plastic. You seldom need lengths of more than several cm, there is hardly any use for lengths of 30 cm. You can sometimes pick up large or coloured sheets on modelshows (for boatbuilding) against interesting bargain prices.
To work with plastic you need a very sharp tool, called scrawker. You can't buy scrawkers, you need to make them yourself. A scrawker is a cutting tool that is used as a knife but cuts like a saw. It can be regarded as a saw with only one tooth and the name is an amalgamation of scratching and drawing. Such a tool needs to be made from hardened steel using an (old) sawblade or cutting blade and knife holder. A minidrill with grinding wheel will soon turn this in a form like this:
___________ | _________ V sharp edge.
The sharp edge is flat and the
width can be varied. I have several for different widths of cuts.
You use a scrawker by drawing along a ruler and pressing lightly.
A sharp scrawker immediately makes a groove of equal width and
leaves a nice plastic swirl. To cut through plastic use a lot of
light cuts instead of a few cuts and pressing hard. You can also
use it to make strong T sections by cutting halfway into the
plastic and gluing a strip vertical into the groove. Only for the
thinnest of sheet of 0.1 mm and such you can use a scalpel for
cutting but generally I prefer one sided razor cutting blades.
Other tools that come into use are things to measure like a
caliper and steel ruler with 0.5 mm index and a small setsquare.
I use a digital caliper because you can use it to make offset
measurements and it is less prone to misreading. It is slightly
more accurate than a normal caliper and but it eats costly
batteries. Against the rules I also use a caliper to scratch the
measurements on the work. Its my tool and I use it as I see fit!
But don't do such things when you cannot afford a new one.
Forget stories of people who think
they can work to the last hundredth of mm. They simply cannot
measure. You need sophisticated (and calibrated) equipment and a
laboratory to work in. (I know something about measuring!).
Besides that you generally won't notice any differences below 0.1
mm unless edges are very close together and the model sits within
a few cm of your nose in lots of light. Apart from that you can
always use painting techniques to cover up small irregularities.
Other useful tools are various scraperboard knives. They look
like old-fashioned inkpens without split but are thicker and not
for writing. You can buy them in art shops. I use these to scrape
away burrs or scrape off material to produce tapered sides or
rounded corners.
I can only say don't use glue! I use solvent to make from 2 pieces one firm structure. The solvent I use is for thinning contact glue from a well known Dutch brand with turquoise striping and a buffalo as mark. Can be bought in any DIY and is 10 times cheaper and better than any glue from your modelshop. It is very thin with a low contact angle and therefor runs easily into the farthest corners. It solves the plastic but leaves the surface intact as long as you don't touch it and don't spill drops. But the main reasons are, that it works very fast, even better than most superglues, and that you can first bring the pieces together for a good fit and then apply the solvent. I use a small brush to apply a limited dose.
It won't be long before you will come to surfaces that are not flat but curved in one or more dimensions. A roof of a wagon for instance. You can make curved forms in plastic sheet in different ways. Simple forms like rounded corners can be built up with thicker pieces fixed on the inside and sanding, filing or scraping away on the outside. For the other methods you generally first cut an oversized piece to work with. Curved roofs can be made by forming the plastic into a curve by pressing with a rounded dowel on the plastic lying on a flexible surface e.g. a piece of thick rubber. In this way you can make quite complex forms. Alternatively you can built a roof from thin layers glued together in a curved form. More complex forms can be made by hot forming over a warm mould. By using a metal former on a hot plate the plastic can be melted into form with some gentle pressure of a weight. I used this method with success for making louvered panelling for a diesel.
What you should never do for fine work is cut halfway through your plastic sheet and then break off along the line. This will give you an irregular face and the cleaning of that takes much more time than making a few extra cuts.
author: Henk Oversloot
date: 9 february 1999
