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Aircraft modelling masterclass – Dealing with vacform transparencies

19 Dec
2011

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Picking up from last month where I described how to deal with transparent parts, here I discuss the subject of canopies further. The first step in acquiring these more advanced techniques is to gain the skills needed for working with vacformed transparencies, both those you have made yourself and those you have purchased.

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Aythor continues his back-to-basics series using a Seafire as his example, describing the techniques he uses in making and working with vacformed transparencies.

In order to make your own canopy you will require some form of master. Since most of us will be using the kit part as a master let’s start there. In this case the clear part has been mounted onto a blob of Milliput Fine putty. During set up, the Milliput is trimmed away from the canopy edges so that a sharp edge will be produced to clearly define the canopy part (Photo 1). When the putty has cured, drill some holes around its base so that the clear sheet will be sucked right down onto the surface and edges (Photo 2).

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Ensure that the canopy is polished, clean and ready to be put to use. One can either make a small vacforming ‘box’ or purchase one. I made my own but it ended up being too large for small pieces like canopies, so I took advantage of a small one produced by Kingston Works. This ready-made unit comes complete with frames that clamp together and clear sheets so that it can be put to immediate use. One also requires a vacuum machine, along with a heat source – a pair of oven gloves is also a good idea (Photo 3). When setting up for production, ensure that all the objects needed are within a tight circle so that they can be readily accessed. In this case use was made of the electric stove and our portable vacuum cleaner. One must ensure a tight fit of the vacuum hose to the machine’s outlet and in this example Duct tape was wrapped around the hose until a tight fit was achieved. Next, a section of clear plastic is mounted in the clamps and one of the stove heating elements is turned on to high heat. Ensure that the part to be vac-formed is in the centre of the perforated surface and then hold the clear sheet over the element until it softens and droops. With the vacuum on, carefully but quickly place the heated sheet of plastic over the canopy and down to the perforated surface; ensure the gloves are being worn! With practice, you should be producing useable clear parts. Once the plastic has cooled, then the new canopy can be cut away using the Milliput mount as a great cutting guide (Photo 4).

Aftermarket canopies

Needless to say, there is a plethora of aftermarket vacformed replacement canopies available. The first step in using these is to mark the cutting edge of the individual piece, in this case with an inexpensive fine-tipped pen from a drafting store (Photo 5). With the edge clearly marked, carefully use this as the cutting guide and lightly pass the back of a new No. 11 blade along the line until it cuts the thin plastic (Photo 6). An alternative is to use a pair of the small, good quality scissors that can be found in the ladies’ make-up section of many stores (Photo 7). Another alternative is to use a very fine-toothed razor saw (Photo 8). Not shown in the photographs is the use of tape that not only marks the edge to be cut but can also protect the plastic from stray cuts. Any corrections to the cut edges can be carried out with sandpaper or, better still, a small steel file.

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After masking and painting are completed any additional detail can be added before the sliding canopy section is added to the model. In this case the PART photo-etched release handle was mounted and a cable joining its two small holds was added from fine copper wire. The emergency release handle was fabricated from wire and a ‘dollop’ of five-minute epoxy for the ball (Photo 9). The Seafire features an armoured glass panel on the inside of its windscreen and

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this was made from a section of clear injection-moulded plastic. The attachment points around its perimeter were made from stretched sprue and the painted assembly can be seen in Photo 10 before being added to the model.

Fixing the canopy in place

While there are several options for gluing the canopy to the kit, I normally start with PVA (white) glue (Photo 11). This allows the part to be moved into place and any excess glue can be carefully removed with a water-moistened paint brush. Once the permanently attached canopy sections (windscreen and rear panel) are in place, then they can be either attached with the PVA, or, as I normally do, with a ‘swipe’ of five-minute epoxy. The latter will not only give a secure join, but it is an excellent filler and with practice will produce a smooth transition from fuselage to framing. The trick here is to use a small amount of spittle on your finger tip and in one smooth and even motion slide it along the join (Photo 12).

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Painting and polishing

Once the masked parts are attached to the frame, spray a coat of the cockpit interior colour over the entire area (Photo 13). This is done for two reasons. First, it ensures that when you look into the cockpit interior the canopy framing is painted the appropriate interior colour and not the exterior camouflage colour. Second, it acts as a primer and any flaws can be corrected before the exterior coat is applied, With painting and weathering complete it is time to remove the masking. This is normally done with a wooden tooth pick that has its tip cut into a chisel shape. The removal process is carefully started at one corner (Photo 14) and the masking is steadily encouraged away from the part. Depending on what masking material you have used (in my case mainly bare metal foil) there can be a sticky residue left on the canopy face. One of the best and easiest ways to remove this is to spray a cotton bud with some WD-40 graphite lubricant (Photo 15) and rub it off. Once the parts are cleaned they can be carefully polished in place, or for even better results apply a coat of Klear/Future (Photo 16), which will give a sparkling finish. Very few things wreck a model more then poorly painted and attached clear parts. Judging by local competitions, it is one area of aircraft model building that requires more attention from many model makers.

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