I'm building half a dozen devices that require me to mount several slide switches in a plastic enclosure. To cut the rectangular hole for the switch, I usually just drill a couple holes next to each other, and then square it all up with a sharp hobby knife. But that's pretty time consuming and dangerous, as I've broken more than one blade in the process of cutting through thick plastic.

Is there some kind of tool I can use on my drill press to cut square holes in plastic?

Andy,

What you need is a Square Sheet Metal Punch like this:

yeah, I've got a nibbler tool. The problem is that the rectangular hole for the switch is only 1/4" wide. The smallest my nibblers will do is 3/8", unless there's some smaller nibblers out there.

ante: would one of those metal punches work on 1/16" thick ABS plastic?

Andy,

Yes they work nicely in plastic, aluminium and steel but I’m not sure if they come as small as a quarter of an inch though.

One thing you may want to try for fairly small square holes, is a mortise bit. It is for wood working, it has a spiral drill surrounded by a square chisel. It works on some plastics, haven't tried one on ABS. What I have done is sandwich the material with scrap, then drill through.

here is an example: http://woodworker.com/cgi-bin/FULLPR...7&LARGEVIEW=ON

True, an auger type bit is useless on sheet metal, but will work on maleable plastic like ABS. I have used an Arbor press with dies for things like 15 pin D shell holes and Centronics type holes, the press , a manual mechanical 1 ton , will cost only about 60 dollars, but the Centronics sized die was well over 100 dollars. I have no idea where you could get a 1/4" square die.

For fairly thin plastic, and small quantities you can resort to drilling central holes, the scoring the square shape and snapping off the remaining bits. This will also work in a pinch for light aluminum, provided it is a fairly stiff alloy like 5052, that has been hardened. Unfortunately most face plates for small project boxes likely use 3003 or 1000 series, which tends to deform easily and not snap at the score line.

One other idea is to take the time to make a really nice square hole in a piece of scrap steel, then use it as a file guide on the plastic holes. Drill pilot holes in the plastic, clamp the guide plate to it, then use a small file to finish the hole, the guide keeping you from removing too much material.

Scroll saw does a nice job. I layout tape initially to show the lines. For a slot, you'd need to drill a hole at each edge so the cutout will separate. The hole will create a place to thread the scroll saw blade through.

High speed rotary tool (Dremel). You can get bits to do just about anything.

j.

Does nobody else use 'abrafiles' to cut irregular shaped holes?
For those who are not familiar with these, its like a file that cuts like a saw.
I have one that is 1/8" round, so it just requires a 1/8 pilot hole to get started. It cuts plasic project boxes like butter, the metal diecast boxes are only a little harder to cut.
The corners of the cutout are rounded, of course, but that's easily fixed with a square file.
The abrafile can also be bent somewhat to get to that awkward corner - it is not brittle like normal files.

Klaus

those abrafiles look pretty sweet, i just googled them... not something i've ever seen for sale in the US though, unfortunately