Andrew Birkett's nobugs.org
Now I’m using a 12mm drill to make the proper hole. I’d picked up a few offcuts from a metalwork shop, and this included a useful length of 12mm steel rod. Notice the bit of wood underneath the plate so that I don’t drill straight through into the base of the drillstand. Now, being a relative newbie to metalworking, I made a silly mistake. I had the drill in the press, so I turned it on and locked the motor on (full speed) and pressed it down into the plate. The drill cut through the first few millimetre and then basically stopped cutting. It was still spinning round, but wasn’t removing any material. When I looked at the drill bit, the cutting edges had gained a blue tinge. Oops, I made a basic drilling mistake. Big drill bits have a larger contact area, and therefore generate more heat. You need to run the drill quite slowly when you’re using big drill bits, and possibly use some cutting fluid or oil. Otherwise, you ruin a drill bit. And, since I don’t have any way of resharpening them, this meant I had to buy a new 12mm drill bit! Oh well, that’s a lesson.