SLOPING OFF...
...the Newsletter of Christchurch and District Model Flying Club for...September 2025
MAKING FORMS FOR CANOPIES, COWLS ETC
I think some members will know that I have used Steve Davies’s “Vortex Vacforms” for many years, either to buy the items from the huge range that he has in stock, or to produce one-offs from balsa forms that I have made. This started when I designed my Bombardier CL415 and had the plan and short kit published by RC Modeller (it’s still available through Sarik Hobbies). The rather complicated cowls were so much a part of the real thing that I made a balsa form and Steve produced them in plastic - and will still do so for anyone who wants to make the model.
(It’s a shame that the cowls are non-scale and the real things are much less Barn-Door than mine, but there we go)
In the years I’ve sent forms to Steve he has always provided an excellent product. The cowls are neat and flash-free, the canopies are unfailingly clear and sharp. Any inaccuracies are mine! The stock canopies and cowls are beautifully done - my Mustang had one of his bubble canopies for 10 years and apart from being a bit yellow due to the sun, had not changed at all.
But my latest model, the two-seat Avro 707C at 44” span, resulted in a lesson on what goes on behind the scenes to get this sort of quality. To tell the truth, I was not pleased with the form I put in the post. In F1 terms, I messed up the start, got run off the road at the first corner and struggled hard, avoiding a DNF by the skin of my teeth. The thing was big, taking up all five sheets of 8mm soft balsa purchased from NIck. Then a stupid cut with a fretsaw took off far too much on one side which was only restored by much angst and filler. Sanding and shaping did a bit to restore the proper shape, but it was never really going to be perfect. But off it went.
Shortly afterwards I had a “bad news” email. The filler and glue I used to make good had melted with the heat of the vacforming process and surgery was necessary. Steve very kindly and patiently explained what had gone wrong and what he had to do to put it right and soon after that had made a couple of transparencies. He actually forms a separation sheet of white heat-resistant plastic over the form to hide the balsa grain and can pull maybe three copies before it starts to deform.
Left to right, my form after it had blistered and been repaired by Steve, the separataion sheet vac-formed over the form and sealed over it and finally the canopy, pulled over the new white form. I always ask for two pulls - mishtakes can happen!
The canopy, trimmed to size and offered up to the model, with the first look at the screen shapes and then masked, sprayed with white primer and Halfords Silver, a very reasonable “look” for aluminium. The pilot? - Mr Roe checking the layout
This is what he said:
Hi Mike.
Over many years, we have tried just about every method, mainly in the interest of getting the customer a fast and cost- effective way of getting one or two clear canopies from theirsupplied budget pattern.
Patterns we have received as follows.
- Super glue.... Because balsa has a soft porous surface,, it's fairly unstable, even with the super glue you will see the wood grain if we form straight over balsa.To apply the super glue, we use heavy duty workshop ( blue ) paper towel, fold it in to a 2" square/ multi layer because it’s Gona get hot.
- Pouring the glue on to the balsa pattern,, use the tissue to spread it quickly all over the pattern. Not a pleasant job, the fumes are nasty & dangerous. We buy £20 to £30 at a time... we use a lot. We have also used it to seal machined & sanded M.D.F. The separation sheet just helps hide the wood grain and the white sheet is o.k. To form over 2 or 3 times before the heat & pressure starts to affect it.
- Sorry for the long explanation...... But you may be able to use it some time yourself
- Pouring the glue on to the balsa pattern,, use the tissue to spread it quickly all over the pattern. Not a pleasant job, the fumes are nasty & dangerous. We buy £20 to £30 at a time... we use a lot. We have also used it to seal machined & sanded M.D.F. The separation sheet just helps hide the wood grain and the white sheet is o.k. To form over 2 or 3 times before the heat & pressure starts to affect it.
Foam or polystyrene, it melts, not suitable .
Polystyrene with fiber-glass coating,not suitable.
Hollow balsa, our machine will crush this every time, not suitable
Solid hardwood, yes with superglue & separation sheet,
Solid balsa, yes with superglue & separation sheet,
Solid M.D.F. Yes with superglue & separation sheet,
Super glue is the only thing we have found that penetrates the surface enough to hold and stabilize it to withstand the heat & pressure of vac-forming. - But see warning below!
When heat proof paint, fiber glass coating, sanding sealer etc are exposed to 150 and 190 degrees Celsius they all blister & delaminate.
Example. alternatives.
The balsa pattern we have just processed for yourself, to recast in crystacast cast £40, to recast in vac resin £90
We strive to give the modeller a quick cost affective turnaround..
Why...... Because I'm a modeller,, Plus 37 years of happy customers..
Best Regards
Steve/Vortex
Steve makes it very clear that superglue is exceptionally dangerous and must be used very carefully!