but even a slightly dull cutting edge tends to perform poorly
when machining acrylic plastic.
With a prayer for continued good weather, I struck the fatal blow. Actually, I selected one of the smallest of the four windows and rapped it from the inside with a dead-blow hammer. I started from the center near the edge where it had cracked. As the bond fractured, I could feel and see the acrylic flex. I continued around the periphery, rapping firmly with the hammer until the window was free. Out of four windows, one was removed intact; the others were already cracked.
(It may be very difficult to remove the new windows installed with Plexus MA320. We have heard unconfirmed stories of laminate failing before the bond breaks. It may be necessary to grind through the acrylic and adhesive to remove windows installed by this method. -Ed.)
We traced the outline of the original window onto the rough-cut blanks with a fine-point permanent marker. Using the trim saw, we cut outside the line, leaving 1/8 to 3/16 -inch of material all around. I used the original window as a router guide by clamping it to the blank and following it with the bearing-guided router bit. To assure the pattern would not slip from the blank, I placed double-sided pressure-sensitive tape between them.
The original windows
have a healthy 45degree chamfer on the side against
the cabin trunk. I had the major edge against the blank for the first
window I patterned. There is a gap
between the end of the cutting edge of the router bit and the bearing, and
it is difficult to cut the full 3/8-inch thickness and keep sufficient
engagement with the edge of the pattern. On subsequent pieces
I reversed the pattern, which was much easier to
follow. After the edge was trimmed, I switched router bits and cut the
The profile of the openings in the cabin trunk did not seem to require such a large chamfer, but I was uncertain of the requirement for this feature. In retrospect it may be a cavity to accept excess structural adhesive in the original installation. Some relief may be required, but I probably used more adhesive than was necessary to fill the space. I broke the outside edge by hand using a flat file, which trimmed away any of the paper swarf left as the router cut the protective paper. Fabricating the windows was relatively easy, yet exacting, work. I masked the inside of the window opening with 10-mil polyethylene to keep dust and chips out of the cabin. I used a 4 1/2-inch grinder with 50-grit sanding disks to clean off the original adhesive and caulking. We vacuumed all the surfaces, then wiped the window flange
with alcohol and inspected it carefully to make sure all the caulking
was removed and the surface was sound. Next we removed the dust barrier and
masked around the inside and outside of the window opening.
Building the fixturing was the most time-consuming part of the project. I lashed a 2 x 3 thin stud between the lifeline stanchions to provide a structure to brace against. Then I fashioned a frame using 1 x 3 shop-grade pine and screws. The frame is dimensioned somewhat smaller than the window and shaped to spread the compression forces evenly. With window and frame
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