I want to mount a voltmeter-ammeter in a utility box.
They are a standard size and inexpensive compared to an electronics enclosure.
I have drawn a template for my cuts with a free cad program.

What is a good way to cut rectangles in the cover?
In the past I have applied pressure and cracked it.

What could I use make faceplates for a project box?
All cuts could be done in the lids so I could reuse the box for many projects.
Yogurt lid seems too flexible.

thanks

 

Get a 3D printer. You will wonder why you didn't do this sooner.

 

Failing that, what about a hand nibbler tool?

 

Drill holes near the corners and use a coping or scroll saw to cut the edges. If the cut edges might be too rough, undersize the hole and use a file to finish it.

If you decide to go the 3D printer route, check with your local library to see if they have one. I just found out that mine seems to be offering free 3D prints... Or maybe you have a Makerspace.

 

For making holes and slots, i.e., something were score and break won't work, I also use a saw method. Nibblers will work, if the plastic is not prone to cracking. But if it cracks easily, I use a saw, files, and scrapers. For many plastics, you can flame or solvent polish the cut surface to help prevent future cracking.

Drilling holes can be challenging with ordinary 118° drill bits. The bits can "hog in" and cause cracking. A drill press helps, water can help, and also dubbing off the cutting edges of the bit to get a scraping action helps. For small holes, I am just careful. For larger holes (e.g., >6mm), I dub off the cutting edges if the plastic is at all brittle. Nylon, ABS and similar don't need that. Acrylic (plexiglas) and polycarbonate do.

 

I use an abrasive disk in a motor tool (Dremel) to cut straight lines. I use a conical grinding tool in the Dremel for holes.

 

You can use the soldering iron to melt holes in the plastic and then use a coping saw to cut any shape hole. Finish off with a file.

 

At the bare minimum: You can mark the outline, use a small drill bit to make a line of closely spaced holes around, just inside the line.
Use a pair of wire cutters to sever the links between the holes, then file the nasty edge down flat and square.

This is the "minimal tools" approach, if you are somewhat careful, you can cut clean nice holes.