Step 1: Turtleback JigBen Bennet loaned me the turtleback (TB) jig as we are building to the same size 38.5" wide canopy. We ordered canopy/windows together with Nelson Amen from Todd's Canopies to shave on shipping. The canopies came wrapped well in packing and boxed to prevent damage. I stored my canopy since I'm the last to use the jig and had plenty to work on in Ch 13 when all this was going on. When the jig was available and I'd gotten to a good stopping spot on Ch 13 I started to re-furbish the jig. The shape was good but as you can see from the picture on the left, the aluminum strips needed attention. (Note from when I finished with the jig: removing the TB from the jig the first time can be tough on these aluminum strips if you have any epoxy get through the foam seams - which I did. The next person to use this jig will have to refurbish just like I did, but it's nothing compared to building the jig in the first place). Thanks Ben for loaning it to me!
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Step 2: Inside Layup
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I followed the plans and used Wayne Hick's hinge method for building up the foam strips to lay in the jig. It takes a good bit of patience to get their shape to match up, but they sand easy with 200 grit and would mark them as shown to the left and then sand to the mark. This was not a one step process but probably took me 2-3 iterations to get the fit good. All my joints were not perfectly tight, but there were no gaps greater than 1/16".
I held the foam in place using weights on both ends (resting on the flange of the TB jig) while I inserted screws, once I like the fit of each strip. I screwed the sides where I had access with the jig on the ground, and then turned it up to get the bottom, then back down for the next strip. I filed the tips of the drywall screws to eliminate the sharp tip and maximize the gripping thread into the foam. I only took about 1/16th off the tip with a hand file but this allowed me to feel when the screw was coming through the foam without puncturing my finger as well. I let all the screws be flush with the inside and they were no problem unscrewing after the inside was done. This is a fair amount of work however, I counted 130 screws that I spent about 20 seconds filing on each... as I went along. When all done with the foam strips and glueing the flanges on per plans, I used masking tape to seal off the few joint sections where I still could see 1/16" gaps. I had read and talked to others about difficulty getting the tape to stick, and what I found was that the masking tape would stick fine for about 2-3 hrs but if I left it over night (summer time, uncooled garage) the edges would peal back. I resolved that the taping would be fine, but that I needed to tape it and then get started with the micro, layup,... The only thing I varied was taking the 1" wide masking tape and cutting it lengthwise into strips about 18" and 1/2" wide. I figured this would reduce the surface area that the masking tape was blocking from direct glass/micro/foam adhesion while still providing enough area to seal off the 1/16" or less gaps I was taping. This may have been overkill on work since I was using scissors to cut the tape. A better investment in time would have been to tape ALL the seams. When I removed the TB from the jig it had some trouble (described next paragraph) due to epoxy seeping through extremely thin gaps (not the big ones that I could see) and touching the aluminum strips in the jig. I had help from two of my sons with this large layup which was nice given the 88 degree temperature in the evening when we set about getting the inner layup done. We had all the pieces of UNI pre-cut and fitted dry in the jig to make sure we could focus just on alignment and wetting out once we got started. I did the micro work on my own, and quickly learned that I needed to work fast and used the squeege with 80-100 gm batches (I don't like making batches of epoxy any larger than this, to insure it gets spread before it starts to set. In this case I was using MGS 335 with 100% slow hardener and had no problems what so ever. Once spread, this slow hardener will take several hours to set. |
Step 3: Bulkhead and Drip Rail
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I followed the plans for the bulkhead and merged various pieces of 3/8" foam since I don't have a lot of this at the moment. Even though my turtleback is wider than the plans, the center supports still go in the same place as the seats haven't moved. I traced the turtleback outline onto the assembled foam to have a good match by setting the bulkhead up against the big end of the turtleback while in the jig (I used a straight board across the flanges to but the flat bulkhead edge to, and had someone assist me holding it while I did the trace following the inside edge of the glass that I'd already had cured on the inside of the TB.
I used single pieces of BID to do the bulked layups on both sides (which consumes more material but made keeping fiber alignment and speeded up the layup process. Knife trimming was really helpful here, as it only left a little bit later for finishing the edges with the multi tool. Once both sides were complete, I started fit checking in the exact spot where it would fit in the TB and fine tuned the edges slightly to get a good fit and BID tape it in place per plans. Drip Rail: Again following plans here. I did use plastic sand bags to weight down the drip rail and insure conformity of the glass to the curves, and this meant doing the layup in 3 sections and rotating the jig for each so that gravity would help with the sandbags. I had some difficulty removing the duct tape when done, but following others, didn't worry about it since I can fix this later when the cut line is actually cut. Finally ready to remove the TB from the jig... |
Step 4 Glassing Outside of TB
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Removal from the jig was not easy, as I'd gotten some epoxy leak through at foam seams in a few places. In most areas it released with a more deliberate pull upward from the flanges, but you don't want to over stress the flange! In the worst spots I used a stiff putty knife (1.5" blade) sliding between the foam and the aluminum strips to get release. In one spot the epoxy had spread over the under side sufficiently that I had to tap with hammer on the handle of the putty knife to get release. Once released, I could see the problem. I again returned to hints from others which lead back to Wayne Hicks use of dremel to carve out the epoxy and re-fill with pour foam. I got some advice that using "Good Stuff" aerosol foam would work in place of Pour Foam, and since I had some I used it. THIS WAS A MISTAKE. The Good Stuff foam is more elastic and when you sand the outer surface it depresses and then releases back when you remove the sand paper. Most of my problem areas were where the Windows would be, so I smoothed out the foam overall, and then did a little more local removal of the Good Stuff with sand paper and my finger. The result was OK, but not great when the outer layup was completed. In some places I had not carved out enough of the Good Stuff and it gave the glass a slight rise. I'll now have to deal with this in the final contour and finish phase...
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