Making holes for panel pots and switches has always been a major pain in the butt for me.
I tried lots of times to make different sized holes with standard metal drills on tin sheets but the holes always came out at the wrong places or, due to the fact that I don't have a drill stand, triangle shaped because of my inability to keep the panels from sliding up and down the drill. They also came out with lots of scrap attached to them (I cannot find the right word but I mean the metal goo that remains at the opposite side of the drill entrance).
Today, I received in the mail a... STEP DRILL!
Didn't know it's existence till recently but using it has been a revelation!!!
Also I got three tools to make the holes tapered (the smaller two are pictured).
If you are careful with the step drill you get instant holes at the desired diameter (the numbers on the drill are mm). And since there is a taper leading to the next, larger diameter on the drill, you get instant metal-goo cleaning and flattening. No more scrap at the holes...
The following is a 5mm hole. No other tools used!
Below is a 5mm hole but treated with the taper tool afterwards. You can house nicely a 3 or 4mm screw with tapered head.
And the big one.. 10mm for audio jacks and some cheap pots. Instant gratification.
Same rules apply though. If you want to be as exact as possible, first start with a small drill (eg 2mm) to mark the center so as the step drill has somewhere to land.
I would really like to know how other people make their panels and especialy the square shaped holes. This has always been a mystery to me :)