Hi Dave- Enjoyed seeing you and wife at the Lake Pleasant affair in Feb. Stan's info is basically right despite him being so far over-the-hill. The plastic is coated acrylic; Plexiglass is an acrylic. Coated so that the acetone used to clean up doesn't destroy the plastic. When making the windows I used to buy 2 4X8 sheets (a price break at two sheets!) and was tooled up to make them efficiently. I'd tablesaw the sheets, making window-sized rectangles, then bandsaw the windows so that they were slightly oversized, then drill the holes using a jig. Then I'd set the panels on a router jig, which used the holes to locate them. Then a router pattern, which was keyed to the jig by the studs that fit in the holes. Final step was to run the router around the pattern, using a double-fluted 45 degree bit, with a collar guide on the router. Countersink the holes and it's done. Clean as a whistle with no sanding. I could make enough for about 50 boats in a half day if the phone didn't ring. Very important is to drill the holes a few thousanths oversized to prevent cracking. Do this with a number bit. If using #10 machine screws, flatheads to match the countersink, use a number bit that's a bit larger. Don't remember the number. When we started making the 15 we had several windows that cracked at the screw holes because we were too dumb to drill them oversized but finally figured things out. There some tricks to the installation, but you'll figure that out. Important to get the silicone bedding cleaned up immediately. We'd mask off the windows except where they contacted the flange on the house. The machine screws don't need to be tight; a little less than snug. The screws are mostly to hold everythning in ploace till the sealant dries. W. D. Schock, with their neat Santana 20 simply used a clamp to hold the windows in place overnite. As far as I know there was never a problem. An aside- I've seen similar windows that were not beveled but were simply radiused and they looked fine. Not as clean-looking, but much simpler to make. Good luck. jerry ________________________________ From: montgomery_boats <montgomery_boats-bounces@mailman.xmission.com> on behalf of Stan Susman <stanpfa@pacbell.net> Sent: Thursday, May 14, 2020 10:27 AM To: For and About Montgomery Sailboats <montgomery_boats@mailman.xmission.com>; David Grah <d_b_grah@yahoo.com> Subject: Re: M_Boats: Montgomery 15 Window Replacement David, 1/4 or UV stabilized acrylic. You can cut w a fine bandsaw and sand to finish or a router w caution that way you can get the bevel (or radius) at the same time. avoid reciprocating tools as they lead to cracks. air cutting discs can work but if leaned on and tool rpm slows lends to jumping around and cracks. beveled holes for screws lends to cracking. pan heads are better if you can stand the way they look. the plastic expands and contracts more then the fiberglass so at issue is the sealant, must be flexible and yet hold to both the plastic and gelcoat surface. Some sealants have solvents that slowly degrade the acrylic, I don't remember but do the homework. My new boat has a 15 house on it and I took the old windows and the new material to a cabinet shop to cut out. Likely to be someone out there with more details. Try u tubeStan Susman On Thursday, May 14, 2020, 10:02:16 AM PDT, David Grah via montgomery_boats <montgomery_boats@mailman.xmission.com> wrote: I reminded myself the windows of our 1986 Montgomery 15 are cracked at some of the screws, could be bedded and sealed better, and are pretty scratched up. I think there has been discussion about replacing windows, maybe applicable to Montgomery 15's but I can't find it on the photo site and am having trouble downloading the entire history of this group to search, so I'm going to be lazy and ask here. I assume I'd need to fabricate them, so, some questions: 1. What is the best material, type and thickness, for example?2. What is a good source for the material, including tinted gray?3. I hope I could duplicate the shape of the old windows with a pattern bit on a router but wonder if that would melt the material to much. Any suggestion how to cut them out, bandsaw and a file?4. It appears the windows are beveled on the inside of the edges and creating that bevel could create a melting problem like cutting the windows out. What is a good way to create this bevel? Any experience and suggestions are welcome! David GrahBishop California