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What is the best way to trim transparencies?

It is quite awkward to cut say 1cm off the edge of plexiglass, without cracking it.

Then the edges need to be cleaned up so it looks nice.

I am changing the clear cover on the tax+landing light cluster.

Administrator
Shoreham EGKA, United Kingdom

I just took my old landing/taxi light lens to a shop that makes posts / advertisements from plexi/polycarbonate/etc and had them duplicate it in both plexi and poly, including the dozen or so screw holes. Cost about 10 EUR each, fit perfectly. I believe they used one of the digital plotters and some scrap material they had lying around. That said, for me, the lens is pretty much a flat square, with just a slight curvature and rounded edges, which makes fabricating it so much easier – for a 3D shape one would need to also come up with some kind of a mold and some heat skills, as well as use the right kind of plastic.

tmo
EPKP - Kraków, Poland

Acrylic must be trimmed with a fine tooth (14 TPI or finer) bandsaw. Any kind of reciprocating saw is where the cracking risk begins. Otherwise, mechanized sanding. If drilling, the drill must be “dubbed” off, so it has zero bite at the cutting edge. ’Same sharpening as for drilling brass. This is easily searched.

Home runway, in central Ontario, Canada, Canada

Yes, very fine tooth bandsaw. I have also had lots of success using an oscillating saw (often known as a ‘multi tool’ )
Cutting slightly on one side, then finishing from the other helps too. Then sand with medium grade on a block.

United Kingdom

For drilling, one might want to try going the reverse direction, too, especially with a normal drill bit.

tmo
EPKP - Kraków, Poland

Surprised no one has mentioned rotary tools such as a Dremel, and finishing with a sanding block. Far less risk than a band saw and more portable.

United Kingdom

Rotary tools tend to be grabby, and can end up walking across the plexi and scratching it. Small fast turning cutting tools get hot, and then grab and gum up more. Light tools like a dremel tool just don’t have enough inertia, so they are easily snatched away from your intended work area. If you have to use a hand tool, use the heaviest one you can find. The little sanding drums do work well for cleaning up inside corners, but are generally too slow to be useful for actually changing dimensions. If the piece of plexi is low cost, easily replaced, and a hand tool is all you have, sure, go for it. But, if you’re working on a windshield, it’s worth using the best method the first time! After decades of cutting plexi, for better and for worse, a bandsaw is the only way I’ll do it.

Once sawn, it is great to sand the cut edge of large pieces (windshields) to be smooth, and nicely rounded, it’ll reduce stress raisers, which can allow cracks to start in from the edges over time. If you ever get a look at a Cessna Caravan windshield half out of the plane, you’ll see that they are gently scallopped (rather than sharply cut or drilled) to clear each of the center mullion screws, to reduce stress raisers and crack potential. Again, mostly a windshield thing, not really a factor in small or non stressed plexi windows.

Home runway, in central Ontario, Canada, Canada

Over the years I have cut a lot of Perspex, it used to be used in front of TV tubes as a safety glass. It cuts very easily with a hacksaw, i.e. a fine bladed saw, never known it to crack, but then I have never used power tools. For more arkward cuts an Abrafile fitted to a hacksaw frame works well. Drill it with a hand drill slowly, starting with a small diameter drill working out to larger diameters. Edges can be filed and polished if required.

Last Edited by Tumbleweed at 01 Jan 10:11

@Pilot_DAR – OK, for trimming a window or windscreen sure. I was thinking of small components like light covers.

United Kingdom

Do it in s warm place.
(Shoreham instead of Inverness?) :-)

Maoraigh
EGPE, United Kingdom
11 Posts
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