how to cut square holes in enclosures?

[AndyWatson]

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?

 

[ante]

Andy,

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

 

[gerty]

Another thing that works well is a nibbler. just drill a 1/4" hole and insert tool. It cuts a 3/16" wide ,squared end, path. Works on light gauge aluminun, plastic..Cost $10 us...

 

[AndyWatson]

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?

 

[k7elp60]

I have had the same problem with the openings for slide switches. I generally drill the two 1/4" holes close together, then use a round file to make the hole oblong then use a small flat file to make the hole rectangular.

I have even used snap in rocker switches because the cutout is bigger and then the nibbler will work. Or have used toggle swithes as they only require a round hole. Yes I know the toggle are generally more expensive, but the speed of the assembly out weighs the time to file the hole for slide switches.

 

[ante]

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.

 

[zevon8]

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: https://woodworker.com/cgi-bin/FULLPRES.exe?PARTNUM=42317&LARGEVIEW=ON

 

[Dean Huster]

Two problems with the mortising bit idea: (1) it requires a full-size (1/2" chuck) drill press and will cost you about $100 minimum just for the extras to set the press up for it and (2) mortising drills/chisels are HSS and designed for wood, not metal. That's a auger bit down the center of the hollow chisel and it'll catch the first edge of the sheet metal and your world as you know it will come to a complete halt milliseconds after that.

Chassis punches, one of the first ideas mentioned, are great but the smallest one you can get is probably around 1/2" square, if that. The smallest I've seen was 1" square. They're leftovers from the vacuum tube days.

Slide switches have always been a royal pain to work with unless you have a punch press. I think that the arbor press that's often sold along with the other PCB fab stuff in the electronics catalogs is made to do light sheet metal nibbling without having to have a pilot hole larger than the intended hole. You might check that out.

I've used a 1/4" wood chisel with the aluminum held against another soft metal block, such as copper, brass or aluminum. Even though oak is pretty hard, it'll still mash in enough that you'll have to turn the chassis over and use the hammer to flatten it out again. But it gives holes a little faster. You still have to drill a couple of 1/4" relief starter holes for the chisel to work better.

Dean

 

[zevon8]

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.

 

[Oznog]

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.

 

[John Sorensen]

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

j.

 

[Klaus]

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

 

[evandude]

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

 

[stevez]

An alternative might be to use a rotary tool and a template (pattern) to get the shape - this will leave the corners with a radius to match the cutting tool. A file could be used to square the corners, if required. A router with a fine bit would work as well. You might custom make a punch/die similar to the chassis punches that could square the corners.

You could probably purchase a small bit for your drill press that cuts sideways and run it at high speed. Make a template- possibly adding a bushing that fastens to the outside of the bit, that would ride against the template. The opening in the template would of course have to be larger - to account for the OD if the bushing. In this case you would move the workpiece while the tool remained in position.

As with many methods the heating caused by the tool could melt some of the plastic - you'll have to experiment to see if that's a problem.

 

[Glodinone]

I need to punch a 1/4" square hole in sheet metal. Where can I get those smaller chassis punches?

 

[ronsimpson]

I need to punch a 1/4" square hole in sheet metal. Where can I get those smaller chassis punches?

I have so many punches the problem is finding the right one. If I wanted a 1/4" square hole and can not find the 1/4 square punch I would;

>Punch a 1/4" round hole and then use a corner file.
>Use a 3/16 punch like a nibbler.
>Use a 1/4"x1/16 slot punch four times.
>Use a lathe with a very small bit then square up the corners with a corner file.
>Nibblers do not make good straight lines but a file can fix that.

 

[KeepItSimpleStupid]

When drilling sheet metal or plastic use a pilot point bit. It will give a nice round hole.

For a hole 1/4" square, I'd use a jeweler's file to square up the hole.

 

[kimbear]

Dremel

This is the perfect application for a Dremel tool. I bought one a few years ago, and I never looked back. I still have the Nibbling tool...but its painfully slow, although highly accurate.
If it wasnt for societies morals..Id sleep with my Dremel tool...thats how much I love it.

 

[Reloadron]

My suggestion runs with drill a 1/4" hole and fine file it. I doubt you will find a 1/4 inch square punch as for most small punches the draw bolt is 1/4 inch. Also, for what it is worth square punches are pretty expensive tools. Good ones are anyway unless you can find a cheap Chinese set manufactured from case hardened peanut butter rather than quality steel.

A dremel is cool but 1/4" is pretty small.

Ron

 

[KMoffett]

For drilling holes in sheetmetal, you can't beat step drills. They sequentially step from an1/8" pilot up to the size you need. The best thing is that they don't grab the hole on break-out and cork-screw the sheetmetal up the bit like twist drill bits. I use pretty pricey ones, but you can get by with something like these if you don't do a lot holes: https://www.harborfreight.com/3-piece-titanium-nitride-coated-high-speed-steel-step-drills-91616.html Then, you get what you pay for.

Then use a square or triangular file to square-out the hole. I like ones with a "safe" edge.

Ken