On Monday, August 21, 2017 at 9:20:12 AM UTC-4, LongJourney wrote:
On Sunday, August 20, 2017 at 4:18:33 AM UTC-5, Peter Whitehead wrote:
I have replaced a few Slingsby Skylark and Dart canopies.They also used countersunk flat headed screws, but into wooden frames. The trick is to drill the holes slightly oversize and bed the canopy onto a sealant which doesn't have huge and permanent bond strength. You just might want to use the frame again, as I did. Not metal tubular frame, but of similar vintage. Pete

Thanks, Scott. I have located said drawing and see that it was originally fastened with countersunk screws. I also heard from another Austria owner who told me that his canopy was fastened with screws. In addition, I scraped away some of the rubber black stuff on the frame and there are holes about every 4 inches. I have ordered screws and an acrylic drill bit from AS. I plan to drill the holes in the plexi a bit oversized to reduce stress and allow for expansion and contraction.

Thanks for all the help.

I have installed about 20 canopies using screws. I NEVER drill holes. I create the holes using a rotary tool (Dremel) with a cone shaped diamond cutter about 1/8 inch in diameter. Gently pushing the spinning cutter does a combination of cut and melt that makes a good hole and does not create the issues that lead to cracking when a drill is used. After the primary is through, I walk in a circle to increase to final size. If flat head screws are used I make sure the primary hole is a little oversize so that when I countersink I don't get to a sharp edge on the far side. I countersink with a "normal" countersink that is sharp. I use low pressure and back up the plastic so I don't stress at the hole.
FWIW
Good Luck
UH