The ABI ports are beautiful heavy cast and polished bronze, but a challenge to install because of the downward-slopping flange, height that allowed no margin for error when placing them, and the two different radii for the top and bottom corners (See October 25 post). My basic plan was to follow the method that worked for the Ta Chiao ports (See November 1 post.), but this one would be a bit trickier.First step was filling part of the old port hole recess to accommodate the shorter ABI port. This time I used the thinner glass fabric rather than heavy roving, which worked out better. Although it required even more (40+) layers, it was easier to handle and allowed more a more precise build-up, which resulted in much less filling and fairing. Cutting as many as six layers of fabric at once sped up the process. Still, it took most of the day Saturday to grind away the old caulk, grind a bevel to receive the new fiberglass, lay up the fiberglass, grind it flush, fill and fair it. In what was left of the day, Scott helped me tighten up the bolts on the leaking doghouse skylight. In the process we discovered that my previous helper hadn't been too good about getting them really tight, and at least one was stripped and not doing anything. I'm optimistic that we will have conquered the leaking skylight.
Once the hole had been filled, I used the template I had made previously to place the new port and mark the locations of the centers for the four corner holes. These four points were critical as they would determine the size and location of the entire cutout. Because of the size of the interior mounting flange and the limited space on the cabin side, I had to get it right.
I used an adjustable bevel gauge to capture the angle of the sloped flange on the port and then set the angle of my drill guide. I used the drill guide to drill pilot holes which in turn guided the hole saws that were too big to use in the guide.
The resulting four holes determined the cutting lines for the jig saw cuts that would connect them and complete the cutout. The top and bottom cuts had to be angled, so I used the bevel gauge again to set the saw blade angle.
Once the angle was set, I screwed some scrap to the cabin side to guide the saw and made the cuts.
But no matter what type of jig is set up, a hand jig saw is not a precision machine tool. The blade is held only at one end, so it tends to flex, especially when cutting at an angle through thick hard material like fiberglass. So I wasn't surprised that one of my cuts was less than perfect. I had anticipated some careful grinding would be required back in October when I made my test panel cut-out. Alternate grinding and trial fitting eventually got the job done. It also turned out that I was about 1/8 of an inch too high in my placement of the cutout, so I had to grind away a bit of glass on an interior stringer where the ceiling meets the cabin wall. Not difficult; just very messy, throwing fiberglass dust everywhere. 
With the cutout completed, I epoxied the exposed edge of the plywood liner and filled the gap between the liner and the fiberglass with epoxy putty. I had hoped to get the port installed and sealed up by the end of day on Sunday, but I was running out of daylight fast. I set up an infrared heat lamp to try to speed up the curing of the epoxy.
I had hoped I could cut and place the butyl tape around the port while the epoxy cured, but it was just too late and the epoxy wasn't curing in time. It would have to wait until the next dry weekend. I had no choice but to temporarily cover up the hole with plastic sheeting and duct tape. I had just enough energy left to clean things up enough to go home and recuperate.
But no matter what type of jig is set up, a hand jig saw is not a precision machine tool. The blade is held only at one end, so it tends to flex, especially when cutting at an angle through thick hard material like fiberglass. So I wasn't surprised that one of my cuts was less than perfect. I had anticipated some careful grinding would be required back in October when I made my test panel cut-out. Alternate grinding and trial fitting eventually got the job done. It also turned out that I was about 1/8 of an inch too high in my placement of the cutout, so I had to grind away a bit of glass on an interior stringer where the ceiling meets the cabin wall. Not difficult; just very messy, throwing fiberglass dust everywhere. With the cutout completed, I epoxied the exposed edge of the plywood liner and filled the gap between the liner and the fiberglass with epoxy putty. I had hoped to get the port installed and sealed up by the end of day on Sunday, but I was running out of daylight fast. I set up an infrared heat lamp to try to speed up the curing of the epoxy.
I had hoped I could cut and place the butyl tape around the port while the epoxy cured, but it was just too late and the epoxy wasn't curing in time. It would have to wait until the next dry weekend. I had no choice but to temporarily cover up the hole with plastic sheeting and duct tape. I had just enough energy left to clean things up enough to go home and recuperate.News flash: The new oil pressure sensor arrived today, so I will hopefully be able to solve my engine instrumentation mystery soon!
One again, i am baffled how you can carry all this neurosurgery in your head and parallelize all this effort into only 2 days of work - with time for adjustments and unplanned problems. 40+ layers with curing time and precision measurements in 3D space. Baffling.
ReplyDeleteQuestions for this week:
- how did you center the cutout against the cabin?
- filling in - assume the blue is where you filled?, although I see there is texture in the middle of the window which indicates it already has some sort of filling? What is that?
To be as efficient as possible while doing the hands-on work on the weekends, I go over everthing mentally during the week (usually while lying awake in bed) until I think I have worked out how everything will be done step-by-step. Doing that also helps me determine what tools and materials I'll need to have on hand.
ReplyDeleteTo center the cutout I positioned the template, took measurements, repositioned and remeasured until I thought I had it right. Because of the curved sheer line and slopin cabin top, some final eyeballing was used to make it look right (not necessarily level). The difficult part was trying to figure out the inside clearances because there were no corresponding places inside from which to measure. I did the best I could and ended up about 1/8" from optimal.
See next comment for the answer to your second question.
Here's the story on filling in the end of the old window cutout...The original windows and frames had been removed entirely. What you see within the cutout in the first photo in this post is the back side of the plywood interior liner covered with a thin layer of caulk. More caulk was used to try to seal the joint between the plywood liner and the fiberglass edge of the cutout.
ReplyDeleteAfter grinding away all the old caulk in the area that needed to be filled and beveling the edge, I filled the left semicircle of the original cutout with fiberglass. The darker parts in that semicircle are the sanded raw fiberglass, the lighter blue areas contain filler to even out the lower spots. To build up the layers quickly, I precut the fabric in semi-circles of varying sizes to fit the changing area created by the bevel. The pieces were cut and stacked in the order I would place them. I mixed enough epoxy to do them all at once if I worked quickly, which I did. The day was cool, so I had enough pot life. I shined the heat lamp on the cutout area to speed the curing once the fabric was laid up. Each layer of cloth was layered on the previous wet layer and pressed down enough to stay in place while I applied more resin with a foam brush. Only took 20-30 minutes to do all the layers once all the set-up was done.
Great breakdown. Thanks Capt George!
ReplyDelete