Paul 5r4
Well Known Member
I just finished all the Plexiglas work including the rear window. For the better part of the past three years I have been, like most builders, really worrying and sweating about the work on the canopy and in particular the cutting, drilling and countersinking the Plexiglas. After completing this work, I realized I wasted lots of brainpower and lost way too much sleep over this. I have 100 percent confidence that if I had it to do over I could do it without worrying about cracks. It's just not near as bad a job as I thought it was going to be. In a nutshell here are the things I did and did not do.
1. Set my thermostat in the house to 80 degrees, (I'm building in the house). I waited a couple hours giving the canopy time to warm.
2. When cutting and trimming of the canopy I used the cut off wheel sent by Vans and it works great. At first I tried to use this in a die grinder however my air supply was too small. I have an electric drill which I ended up using. This drill can achieve some very high RPMs.
3. Once making a cut was completed, I filed then sanded the edges before moving the canopy back to the airframe. Yes this was a bit time-consuming however moving a canopy which will certainly cause flexing of the Plexiglas, would be asking for trouble because of the thousands of near microscopic scratches and cuts along the edges.
4. Drilling: (Use a variable speed drill), after doing several experiments on the scrap pieces this is what I found. I pilot drilled each hole with a regular number 44 drill bit in that high-speed drill. The holes were brought out to my final size of 3/16 using a unibit. The 3/16 hole gives the Plexiglas room to contract or expand as needed. When drilling the holes with the number 44 drill bit I used a pretty high-speed and very light pressure. In all my experimentation, the only time I cracked any Plexiglas was when breaking through the backside. When drilling with the unibit I would get a very fine chatter for just a second until the sides were down inside the Plexiglas. Once again, I stress the point of not using much pressure especially when breaking out the backside with the unibit. Any excess pressure here will almost certainly guarantee a crack before your finished. It's hard to describe but if you practice a few holes on some scrap you'll find that right combination of RPMs and pressure. It just feels right, looks right and sounds right.
5. For countersinking I did not use one with the pilot which would fill the 3/16 hole! Started to do this on one but it was real tight... too scary. I used the next smaller size. Here you have to go pretty slow with the revs. The pressure used was just what it took to make a chip. If it starts to chatter, stop and have a straight on look at the job so far and you'll see a "skinny" side. Lean the drill/counter sink toward that skinny side and it will stop chattering and even out the c-sinking job. They all came out nice with the hole properly centered in the countersink.
I encourage you guys who have not reached this point not to worry. I know that's easier said than done but this simply wasn't near as bad as I had anticipated. Recently I read a post somewhere on here that once you complete the canopy, it's all downhill from there. I hope so. Within the next couple of weeks I hope to move my airplane out to my hangar to put wings, tail and engine on.
Hope this helps and good luck!
1. Set my thermostat in the house to 80 degrees, (I'm building in the house). I waited a couple hours giving the canopy time to warm.
2. When cutting and trimming of the canopy I used the cut off wheel sent by Vans and it works great. At first I tried to use this in a die grinder however my air supply was too small. I have an electric drill which I ended up using. This drill can achieve some very high RPMs.
3. Once making a cut was completed, I filed then sanded the edges before moving the canopy back to the airframe. Yes this was a bit time-consuming however moving a canopy which will certainly cause flexing of the Plexiglas, would be asking for trouble because of the thousands of near microscopic scratches and cuts along the edges.
4. Drilling: (Use a variable speed drill), after doing several experiments on the scrap pieces this is what I found. I pilot drilled each hole with a regular number 44 drill bit in that high-speed drill. The holes were brought out to my final size of 3/16 using a unibit. The 3/16 hole gives the Plexiglas room to contract or expand as needed. When drilling the holes with the number 44 drill bit I used a pretty high-speed and very light pressure. In all my experimentation, the only time I cracked any Plexiglas was when breaking through the backside. When drilling with the unibit I would get a very fine chatter for just a second until the sides were down inside the Plexiglas. Once again, I stress the point of not using much pressure especially when breaking out the backside with the unibit. Any excess pressure here will almost certainly guarantee a crack before your finished. It's hard to describe but if you practice a few holes on some scrap you'll find that right combination of RPMs and pressure. It just feels right, looks right and sounds right.
5. For countersinking I did not use one with the pilot which would fill the 3/16 hole! Started to do this on one but it was real tight... too scary. I used the next smaller size. Here you have to go pretty slow with the revs. The pressure used was just what it took to make a chip. If it starts to chatter, stop and have a straight on look at the job so far and you'll see a "skinny" side. Lean the drill/counter sink toward that skinny side and it will stop chattering and even out the c-sinking job. They all came out nice with the hole properly centered in the countersink.
I encourage you guys who have not reached this point not to worry. I know that's easier said than done but this simply wasn't near as bad as I had anticipated. Recently I read a post somewhere on here that once you complete the canopy, it's all downhill from there. I hope so. Within the next couple of weeks I hope to move my airplane out to my hangar to put wings, tail and engine on.
Hope this helps and good luck!
