Dave- sorry, I should've been more clear. As chip noted the basis is stertching a piece of clear sheet over the original canopy after heating. FSM magazine had an article on a build your own Vacuform in the May 2000 issue. If you already have a stove & a vacuum cleaner w/ a hose, the rest is cheap & easy. (I'd scan the article & send it to you but my home PC took a dump- all my online is at work now...)
1. press the old canopy into some modeling clay for a clean impression. Pour some plaster into this impression for a "plug". Trim the excess but leave about 1 cm below the edge for a stable mount. If you can get a small undercut at the bottom of the canopy frame, better yet.
2. while this is drying, (at least 24 hrs) purchase some .015-.020 clear sheet; A fisherman's lead sinker box ( these are about 10cm wide, 5cm high, & cylindrical. they're threaded both sides, and have a lid that screws in. Get 'em from a fishing or sporting goods store.) Some masonite board(1m sq. is plenty),
duct tape, and a couple of large binder clips.
(someone may need to translate that stuff to godzone for ya, but I'm clueless...)
3. Cut a hole in the LID of the sinker box w/ a hole saw, close as possible to the size of your Vacuum hose. Drill a lot of hloes in the bottom of the box, 1 cm apart should do it. Cut a hole in the masonite just slightly larger than the diameter of the box, about 5cm from the edge of the board. Then trim the board in the shape of a short cricket bat around the hole.
4. screw the lid to the box, then FIRMLY attach the "plug" to the base with all of the holes drilled in it. 'Aleene's' Tacky Glue is ideal for this.
5. Insert vacuum hose into hole in lid, use duct tape to make it as airtight as possible.
6. Clamp a piece of clear sheet onto your 'cricket bat' with the binder clips. this sheet should be about 3cm larger than the hole in the 'bat'. Take all of this stuff over to the hose.
7. Turn on stove element (that's one of the small top cooking surfaces) and hold your 'bat' about 10-12cm from the heat, plastic sheet facing up.
8. turn on vacuum & wait. I like to duct tape the hose to a counter next to the stove so I don' have to go through contortions on this next step.
9. AS SOON AS the plastic begins to sag through the hole in your 'bat', IMMEDIATELY invert it and draw it down around the sinker box & plug. If the sheet is soft enough, the vacuum will shrink the sheet tight around the box & plug.
10. turn off stove, after aminute or two turn off vacuum. If it all went right-
11. Trim plastic around plaster plug at line of orig. canopy frame- Viola!
Don't get discouraged if you cock-up the first few tries. It takes practice & patience, but once you get the hang of it you may wat to replace every canopy an every A/C you've ever built
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!
I hope you can use this as a jumping off point, and don't hesitate to ask for clarification!
HTH- RobH