We recently had new casement windows installed (17 of them

I am quite pleased with how the adapter turned out. I bought an extra screen from the window supplier to modify, so that the original screen can go back in after AC season, leaving the rest of the window " as installed".
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The above photo shows the lower 2/3 of the window bug screen covered by a piece of shatter proof acrylic plastic with a hole cut to suit the air conditioner hose end.
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I cut the perimeter of the plastic sheet and the plywood retaining pieces with a fine tooth blade in the Shopsmith band saw and then smoothed them up with the drum sander in the SS drill press. The hole was cut using a fine tooth blade in a Craftsman sabre saw that I bought around 1970 and also smoothed using the drum sander.
I used #10 bolts through the plastic (they were what I had!) to hold the hose to the hole with washers under the bolt heads to spread the load.
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The plastic is fastened to the aluminum bug screen frame with short metal screws that do not penetrate right through the frame. I cut small openings (slots) at the plastic sliding bug screen catches to make them accessible.
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It looks ok from outside, fits in the window without a struggle and will be easily removed for the cooler months!
