Why that person went to the trouble of framing an acrylic door, I don't know, because acrylic's normally more expensive than glass, and if you are making a frame around it anyway to stiffen it, glass would be the way to go. Glass doesn't scratch like plexi. Sorry, just a side comment on the photo.
ANYWAY....
Well, it looks like they used aluminum U channel to make the frame for the glass in that photo. A hardware store or metal supply store would have this kind of channel. How he attached the channel pieces together is a guess, because it's very difficult to see... perhaps glue/epoxy, perhaps screws, perhaps small corner connectors like those used to hold window screens together.
I make stained glass artwork as a hobby, and regularly use copper and zinc U-channel (called came) to make outer sturdy frames for rectangular pieces. The corners are soldered together in that case. If you decide to try this route, find a stained glass supplier in your area, and ask them for Copper or Zinc U-came. They make it in different depths for different thicknesses of glass, and different widths to make wider or narrower frames. Since you'll be using this around animals, you can get non-lead solder to use so your animals won't touch a lead solder joint and possibly get poisoned. Stained glass supply houses usually carry lead-free solder as well, and you'll need flux to prepare the joints for soldering, and a large soldering iron (80 or 100 watt).
You can then mitre the corners to be 45 degree angles - measure precisely so your glass has room to fit before you cut. Solder the corners together, putting the glass IN the frame before you solder the last part of the frame together. Do not overheat at this point or you'll wind up with cracked glass.
If you want a waterproof, rattle-free door, you'll need to get some glazing putty to force between any loose gaps between the frame and the glass. Be careful when planning for a hinge - attach it to the door before you put the glass in, so you don't shatter the glass later trying to attach the hinge to the door.
Anyway, you could probably use wood trim to frame a door as well. You'd need either trim that was already cut with a rabbet in back (a recessed area to allow the glass to sit), and then you can use glass-door clips (from a place like Rockler.com or a hardware store) to hold the glass in behind the frame. Or you'd need a router in order to make a channel for the glass to sit in the wood frame. Lots of ways to do it.
Hope this helped you out a bit.
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Lauren Madar - OphidiaGems.com
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