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The Magic of Mylar by Mike Thompson (
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The first time it occurred to me to use a clear template in place of the aluminum skin to place holes was when drilling the side skin in the "Cone Zone".  I'd not been having the best of luck hitting ribs and flanges just right and this was one area that needed to be right on - not to mention trimming the curve so the side skin would lay down well. I thought "Wouldn't it be nice to be able to see through the aluminum skin". My daughter had discarded a poster frame, and the thin plastic which is used in place of glass.  When my eye fell on that, I had it. 

I used the side skin to cut a side of the poster plastic to match, then back drilled through holes already in the side skin, so that I could cleco the plastic to the fuselage frame, essentially making a transparent duplicate of the rear 24 inches of the side skin. As with all experiments mine was not without failure; when I bent the plastic "side skin" around the curve, the forward edge (which gets bent the most) cracked.  Having worked in electronic design (the old fashioned way, before CAD) I knew that I needed a sheet of .032 Mylar. Fortunately Austin has a plastic shop, and a sheet was quickly procured.  Once trimmed to, again, match the rear of the fuse skin, and then back drilled and clecoed to the fuse, I was able to wrap my Mylar around the curve and draw a tentative trim line.  There followed a series of mark, trim, fit, mark, trim, fit until the Mylar layed down exactly the way I wanted.  Since I could see the flanges of the bulkhead, marking the location of rivet holes was easily done. After removing the Mylar and clecoing it to the side skin, my Mylar sheet became a template for trimming and drilling holes. The side skins fit wonderfully and every hole was optimally placed. 

The next time I had use for the Mylar sheet was drilling the cockpit floor panels.  Since no bending is done here, some cheaper poster frame plastic could have been used, but I had the rest of my sheet, so... Rather than attach stiffeners to the floor ribs in order to be able to make a mark at each end, draw a line and have the rib centered along its length, I  trimmed my Mylar around a floor panel (after trimming the floor panel to fit). Laying the Mylar down on the floor, I could see the ribs to mark holes, and if one of them wiggled a little bit, I just followed the wiggle.  I then removed the template, layed it on the aluminum panel and back-drilled the panel, then dropped the panel in the floor and drilled through into the floor ribs. I circled the holes with a red sharpie, flipped the template over, retrimmed for the other floor panel and re-marked the other side's holes in blue sharpie.  I repeated the back-drill and drill the ribs process taking care to use the blue markings for the flip side. This process worked well for the baggage floors as well as the cockpit floors. 

I didn't get out what was left of my Mylar until I started doing the sliding canopy side skirts.  Of course I needed to hit the center of the frame rails, so again Mylar templates were made of the side skirts and here I actually drilled and clecoed the Mylar to the canopy frame - dead center;  back-drill through the Mylar into the aluminum side skirt and simply clecoed it on. 

I also used this Mylar template technique to make my rear canopy skirts, which fit about as well as any I've seen. 

I don't know if any of the work ahead of me will benefit from this method of clear templates, but I'll be on the look-out as I start cutting up my instrument panel.

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