Drilling holes in an UL 508A Industrial Electrical Control Panel

There are two popular size push buttons. A 22mm and a 30mm. Please get the correct size drill bit for the hole.

There are four main ways to drill a push button hole, three of which I recommend.

hole1.pngStep bit - The step bit is capable of drilling a hole then incrementally stepping it out to the right size. I use these on job sites quite a bit where I need to drill an odd hole here or there. The main reason is I’m already carrying everything but the kitchen sink to a job site so it allows me to carry one compact bit to do multiple hole sizes. Like with most cutting tool, buy a good one. Your cheap ones will only last a few holes. A good one will drill hundreds of holes. The main key is not to run the drill any faster than you need to in order to cut the hole, this keeps the heat down and the drill bit sharp.

hole2a.pngKnockout - Most people are shocked to find that I use almost no knockouts. I drill a hundred push button holes some weeks and I've probably used a knockout twice in the past year. And on top of that I don’t even own a hydraulic knockout though I do use a socket on a drill instead of a ratchet. A knockout is made of three pieces. A draw stud which is pretty much a bolt with a bearing on top of it, a die, and a punch. You drill a hole large enough for the draw stud to go through, put the die on the draw stud, insert it through the hole and screw the punch on it until the hole is finished.


Hole Saw - I never use this method unless I get stranded at a job site and have not other option but to borrow someones. The issue is this requires a perfectly straight drill bit. A 7/8 hole saw with a perfectly straight drill bit will drill a 7/8” hole. But if the drill bit is bent 1/16”, it will wobble making it drill a 1” hole. The the slug gets stuck in the end of the hole saw and you have to pry it out with a screwdriver.

hole3.pngHole Cutter - Instead of the hole saw, I use a carbide tipped hole cutter. It is nearly the same thing but if is much more beefy. It has a center drill that gets the hole started, then the carbide teeth cut a fast smooth hole, and there even is a spring to push the slug off of the bit once the hole is drilled. It takes about 3-5 seconds to drill a hole through mild steel, maybe 10 seconds through stainless steel and also cuts well through fiberglass. I’ve used a lot of different brand hole cutters and my favorite is made by Ideal. In fact Ideal should send me samples for saying that. If you think you have a better one, send me your samples and I’ll check it out.

To show how it works, we are going to drill a hole in this fiberglass panel because it presents a few issues that steel does not. Make sure you measure twice, there is nothing worse than holes that don’t line up. Place the tip of the center drill right in the middle of your mark. It has a very sharp point so holes are always accurately drilled. As the center drill breaks through, back off your pressure and ease off the rpm a little bit to allow the carbide cutters to start cutting evenly. Don’t run the cutter fast enough to build heat, the faster you run it, the more heat it will build and the sooner it will dull. Now if this were a steel panel, we would continue on through, but fiberglass is bad about splintering as the cutter is breaking through. To prevent this, stop drilling after the cutter starts cutting evenly, then open the panel up and cut about halfway through from the inside, then close the panel back up and finish cutting the hole. Once it breaks through, you will see that the flange prevents the cutter from going too far into the enclosure and damaging internal components. Also note that the spring on the end of the cutter has pushed the slug off of the center drill and it is ready to cut the next hole. For people cutting fiberglass panels, note that we have a vacuum cleaner right beside the cutter while drilling to catch the fiberglass shavings but we didn’t during this video so you could hear us.

Next Steps

Go to the UL 508A Control Panel Lesson series to select your next lesson.  There are also many other Lesson Series on PLC Programming and Industrial Automation.