MFW June 2013 - Page 10

So to the procedure …. Bear in mind that the old Airsail machine is a small semicommercial unit and features advantages that home hobbyist style units simply don’t have. However as you will see later in Pic 7. there is a pretty simple option for producing some small to medium size mouldings. I’ve been asked to write something about techniques and systems I employ in my model making. Most of what I do is not new and we all benefit from the toils of others. Also, there are some things that I’m simply not prepared (or don’t feel the need) to tackle – some materials I have hardly ever used. I’m what you will call and “old school” modeller however I love some of the new ideas and tricks I come across in magazines and on build sites. Thankfully, there are a lot of very clever people out there who willingly share what they know. One of the great mysteries for some is Vacuum Forming. For many years now most kits - and these days almost all ARF’s have vac formed parts. For a build it yourself model from a plan or a scratch build I know that decisions to go ahead with a project or not can depend on being able to form canopies and cowls. I found myself at the deep end when I became involved with Airsail a lot of years ago. Faced with making kits and vac forming various parts was initially a little daunting but it opened my eyes to what could be done. I hope what you read and see here will give you an insight into the not-so-mysterious black art of the process. As a demonstration I will use the nose wheel door of my Vampire that’s been on the go for more than a little while. Whether it’s a canopy or a cowling of one sort or another the starting point is the plug or pattern. As you see in Pic 1, the nose door pattern has been made from solid balsa. It could as easily have been made from hardwood or MDF Board. A pattern can be made from polystyrene foam, blue foam or polyurethane foam however all of these require glassing and filling to achieve a good working surface. More importantly, they MUST be sealed so as to avoid a collapse under vacuum as all the air within the cells of the material is sucked out. (Take it from me …26 inches of Mercury does not mess about!) This absolute rule also applies a light wooden pattern …it must be solid. In reality, a wooden pattern is best made undersize then coated with Builders Bog or filler laden Epoxy, then sanded to shape. These materials handle the heat better. If you make a laminated canopy plug from Balsa or MDF you will almost certainly see the lamination lines in the finished moulding. This appears to be due to the heat impact of very hot plastic on a cooler mould. Your mould or plug should not be a high gloss but should be finished to a very high standard with 600 grit paper, wet sanded if possible. Every single imperfection will show on your moulding. This is much less of an issue with opaque plastic cowls etc. as they can be easily filled and sanded prior to painting. Clear canopy mouldings are totally unforgiving. Commercial production moulds are most generally made from Aluminium filled Epoxy. Very large moulds may be fitted with cooling tubes to prevent the mould from overheating during extended use. Pic 1. you can see the nose door shape nearing completion. Pic 2. shows the finished article with additions to the sides, the front and the back ends. This is simply to allow some cutting room to allow for better fitting of the end product. Filler has been applied and sanded and the surface coated (in this instance) with Sanding Sealer. Pic 3. shows the heater at work.