I had a look at my canopy "stash" today, hoping I had a 5-6" bubble canopy for the new "ramrod" that I am building.
Doh!, no such luck. I read up on that ACLN article that Jim Thomerson posted the link for.
It took about an hour to "knock up" a plug out of some (heavy) scrap block and I was away.
The first couple of attempts worked ok around the middle (highest point) of the canopy but the front and rear ends wrinkled up and didn't shrink nicely around the plug.
After a re-think, I cut the bottle down enough so that there was enough plastic over each side to be clamped in the vice with the plug. This held it nice and firm so that I could pull the "over hang" down each end with pliers whilst carefully applying heat with the heatgun.
It took 4 goes to get a feel for the technique and produce a useable result. More practice will certainly improve the odds.
For best results use a nice "fresh" bottle that doesn't have any scratches on it and (if possible) use a bottle that has no lines or dimples, so that you get a nice flat, clean sheet of plastic when you cut the bottle up.
The lines and dimples in coke/sprite bottles etc iron out fairly good but they don't totally disappear.
May not be as noticeable on a little 1/2 A canopy, but the larger the canopy is the more the lines stand out.
The best thing is that they are free and nothing is lost in attempting to learn the technique.
I for one will definately be attempting to perfect the method as it will be quite handy to "Knock up" canopies at will.
Cheers, Rob.
P.S Thanks Jim for posting the link!