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 .
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 .
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 3 . shows the heater at work .