Cutting Plexiglas

[wolfie]

Got a slight problem - need to cut a couple oval holes in a piece of thin (0.080") Plexiglas, and am looking for the best way to do it. The Plexi is thin enough that a coping saw would have problems (even a fine-pitch blade wouldn't have 3 teeth in contact, so it would get stuck in the gap between teeth), and because they're interior holes the standard "score and snap" method won't work. Any ideas?

The particular project is fitting a portable air conditioner to my window - needless to say I want to get it done SOON. The hard part of fitting an A/C unit is sealing the gaps, so I figured the easiest way to seal it would be to take the glazing out of one of the sliding sections (aluminum frame) and put in acrylic glazing with the same size holes as the adapter plate (meant to be screwed in place on wood window frames) supplied with the unit. After all, the window frame DOES have weatherstripping to seal it when closed.

My ideas so far:

- Trace the hole from the adapter plate, go over the lines using a craft knife. Lightly at first so I've got more control, then as they get deeper (so that the blade will have a harder time jumping out of the cut) using more force. Once I've got a significant distance (at least a third of the way) into the plexi, try *CAREFULLY* bending along the scored line to break it (and hope I don't ruin the piece).

- Drill a series of small (1/16") holes inside the line really close together, break along the perforations, and file to size.

- Buy a hole saw of the appropriate size, use it to cut the round ends, then score and snap the straight lines connecting the holes.

If anyone else has ideas, thanks in advance.

[ApolloSZ]

You've already thought of most of the ideas I had (drilling the 'corners' as such, or multiple small holes).

Alternately if you have a dremel and cutting discs, or the metal engraver type heads, and carefully (and at low speed to avoid melting) grind it out that way.

Less optimal, a Soldering iron to melt out the rough inner shape (with ventilation etc, good ol plastic melting :| ) and then file/sand the edges tidy.

Been a while since I worked with Acrylic sheets or plexiglass, mainly Plasticard for me these days.


Edit to add - isn't there a diamond wire/string type thread you can get for similar purpose? And then essentially floss your way to victory?

[wolfie]

Looks like the hole saw is out, unless I get the super-fancy adjustable single-point one from Lee Valley. The opening is 3 3/8" wide, and fairly critical (hose end fittings need to snap in), and hole saws go by multiples of 1/4" (or 1/2" in larger sizes).

[ApolloSZ]

You could get the hole saw closest but smaller, then sand/file/grind it out. Do you have a dremel or will it all be by hand? :| lol

[dalesys]

I'd go with the woodburning set.

[lordlundar]

I'd go with the woodburning set.

Uh, nyet to that idea. It will reek in the process, it's too easy to screw up and in any event the iron from it is ruined when you're done.

The knife with a straightedge is the professional method and if you want a clean cut is the best option available. You'll probably have to go deeper than 1/3rd though and put it between to solidly mounted objects that cover the span for better leverage.

[dalesys]

Cutting a circle? Fumes? Outside. Ruined iron? Rosin & sand paper. Or a $5 "burner: at Harbor... I've melted more than a few feet of plastic and I'm perfectly normal.

[BearLeeBadenaugh]

Why don't you just sandwich the plexi between two sheets of wood and then cut like normal? The wood backing should prevent any edge damage and as long as you're using thick enough "bread" you won't have the problem of not enough teeth in contact.

Clamps around the edge should provide enough force, though if you wanted to you could run a couple bolts through the waste section.

Personally, I'd probably use white glue to glue the plexi to a piece of 1/4" mdf and use my router table.

[TheSHAD0W]

You can get *very* fine-toothed blades for jigsaws...

[Arcus]

Why don't you just sandwich the plexi between two sheets of wood and then cut like normal? The wood backing should prevent any edge damage and as long as you're using thick enough "bread" you won't have the problem of not enough teeth in contact.

This is what I do with thin plexi. I get two sheets of plywood (thicker the better) that are bigger than the plexi and screw them together using two sided tape to hold the plexi in place and then just cut it as I would normally.

[csquared]

Sandwich it, or use a RotoZip/spiral saw.

[wolfie]

Thanks for the advice - here's how I did it. I was able to get a fine-tooth blade for my coping saw for a rough cut, then got rid of the lumps (coping saws don't track straight) with a file. Enjoying the ice cold air.