Posted Thursday, August 25, 2011 @ 11:32 AM  

Yesterday was the first day of genuine cutting, drilling, sanding. I probably would fit and measure 3-5 times before cutting. It was a luxury working with the polycarbonate for the open cockpit mod. If I messed up a cut or hole, I could merely cut out a new piece. Not so much this time.

But....so far, the plastic drill is working well. I've found that at moderate speeds (no rpms show on the hand drill...but a little faster than slow), if I use very light pressure, the drill bit will talk to me. If it is squeeking, then I'm using the lightest pressure possible and still have it cut. The shavings are more like a fluff rather than flakes. When the bit exits the back side of the plastic, there is no grabbing just the slightest loss of resistance. I'm also moving the bit around the hole some to "polish" the hole before extracting the bit. So far, I feel good about this approach.

The Rotozip has worked well. The belt sander also seems to be doing well. The belt on the sander is not getting loaded up with plastic with the acrylic canopy material as it did with the softer polycarbonate.

So far, I'm also feeling good about the shrink wrap on the screws. It has held up moderately well to so many times of screwing the canopy down, starting a hole, then unscrewing the canopy, finishing the hole - repeat. Some of the screws will need to be recovered as the shrink wrap is showing some wear. I think this is a good sign that it is reasonably tough -- but soft enough to provide reasonable cushioning.

One thing I learned in the polycarbonate has to do with drilling the holes. You are trying to align a hole through a 1/8" material to the hole on the frame. If you just drill a hole, it's easy for it not to be aligned well. So, I've found that the best technique for me is to try to figure out the best spot, place the bit on my best guess as to the right location, start the bit for a second or so and stop. You've just made a spot (slight indendation) on the plastic. Check the alignment of that spot. If it's off to one side, don't start a new one. Go back to that indentation and drill at an angle toward the place you want...straighten the drill (so it is now perpendicular to the plastic) -- stop -- and now you have a slightly larger spot (indentation). Check the alightment with the target hole. Keep adjusting the alignment of your drilling pretty much all the way to the finish.

If you get the early stage right and the bit is making a shaft in the material, you're alignment is probably right on. But I keep trying to follow the right path all the way through the material. Yes, sometimes I end up with a hole that is not perfectly symmetrical, but it still is just large enough in the right places for the fastener. The way plastic moves, having a little more gap or movement in a hole is not a bad thing, so I don't worry about it. It's all underneath the head of the fastener....so, I simply don't care. I'm not having to drill a second hole or go through heroics to enlarge a misaligned hole (which is the most important to me).

The hangar as been fairly warm, about 77 degrees F -- which probably gives me a little buffer for my lack of experience.

Probably the most challenging thing for me has been the retired pilots/A&P's who have stopped by to tell me how they'd never do any of this to acrylic and how the earth probably will come to an end due to my efforts. They seem convinced that the Acrylic Monster will destroy the project. Being retired, they can take forty-five minutes to say, "I wouldn't do that."

Posted Friday, August 26, 2011 @ 11:11 AM  

Some progress yesterday. Spent almost the entire day on the curve around the back of the passenger seat. I'd trim. It would fit a little better which would move the trim line. I'd trim, the line would move. Many times over.

I also came across the first of my errors. I firmly believe that the proper way to install these is to start in the middle and work outward. I became so engrossed in getting the window vents parallel to the frames and even with each other, that I fixed the portion under the windows first and moved toward the other side. So, as I start to work on the other side, I'm think the canopy is torquing a little as I attach it. The forward section of the canopy extended so far beyond the support that I couldn't clamp it. I should have trimmed off that extra material so I could properly clamp it to the fram from the beginning. So, now when I clamp it down, I see the gap increase at the rear of the canopy -- which implies that the entire piece is torquing a little.

So yesterday I removed all the fasteners and just put on the screws in the back center, then clamped the front center, then started working my way forward on each side (attaching screws as I went into the existing holes). When I did it that way, the forward end showed a misalignment of the canopy holes and frame holes of 1/16-1/8". Granted, just a slight movement of the canopy on the frame can produce that much change. So, I'm not sure that when I did it, that I even had the forward end aligned properly. It was near the end of the day. So, I left it to get a fresh look at it today to better assess if it's a real problem and what I feel I want to do about it.

In general, the Acrylic Gods did not smash this part of the universe, despite the fears of the hangar vistors.

The acrylic is tough enough that I don't make as good a progress with my hand tools as I did on the polycarbonate. So, my hand trimming while it's still on the frame is limited. (Which means I end up taking it off and working on it with power tools on the trimming stand more than I expected.)

My rear cockpit has two sections to the canopy (some don't). I noticed that the support between the two sections uses #6 screws. As my A&P and I looked at it, we couldn't see any reason why you'd move from #4 to #6 screws for that one support. A #6 will make a bigger hole, but really won't have any more useful holding power. Quite possibly in the past, the metal tabs were stripped out and someone just went to the next larger screw. I'm stopping by an aircraft supply this morning to get some Timmerman nut plates for #4 screws to place behind the tabs on that section so I can use the same sized fastener around the canopies. At some point it might be evident why a larger fastener was used....but the #4's seem more than strong enough.

Did a lot of cutting with the Rotozip yesterday including the more detailed cut for the canopy hinge. Seemed to work fine.

Posted Sunday, September 4, 2011 @ 10:50 AM  

Via Collin, Dave Milner sent me a 2007 EAA article that descibes using a product called Plastifix to repair cracks and use a headlight restoration kit to smooth the repair afterwards. It seems promising, so have ordered the kits. Thanks, Dave.

I noted the canopy seal/gasket leaves gaps between the canopy frame & the fuselage in several places. The previous owners of RF5B put strips of household, foam weather stripping around the cockpit to seal those gaps. I'm going to look for a solution that will stay on the canopy frame. There may a way to build some thickness to the canopy seal in those places.

Posted Monday, September 5, 2011 @ 00:40 AM  

I have had mixed results with acetone or solvents. If the pieces fit very well together (especially if they have machined surfaces), then clamping them and introducing the solvent can work really well. The more the break is irregular, has gaps or doesn't fit almost perfectly, the greater the chance that it won't work well.

In this case, I have the luxury of testing the Plastifix on the old canopy which had Plenty of cracks for practice.

Work went reasonably well today. Same sequence as the front with sanding edges & smoothing of holes for the fasteners.

When I tried to install the canopies with the new weather seals, I couldn't get the canopies to fit properly. So, I installed them without the weather seals. Once installed, I went around the edge of the canopies, sliding the seal between the canopy & frame, refastening as I went.

The holes drilled by Thermotec for the Mecaplex windows weren't quite aligned, but it didn't take much adjustment to get the windows on. With the weather stripping installed, the canopies fit a little different. I'd find a spot where the front & rear canopies were touching. Remove the rear canopy, adjust the gap, reinstall. Then find a new spot they were touching. After 5 iterations, I seemed to have a consistent, small gap between front & rear canopies.

After 11 hours working on it today, I decided to save the test flight for tomorrow.

Posted Tuesday, September 6, 2011 @ 01:06 PM  

Old canopies:

New canopies: