Drilling Accurate Holes in Thin Sheet Metal With Twist Drills

[Mark Presling]

Drilling thin sheet metal with regular drill bits can be hazardous and even if you are able to get the drill bit to cut through, the hole will often be oversize, triangular or pentagonal in shape and there will be snaggy burrs all around the edge. The big danger is that the sheet metal will try to lift off the drill table and run up the flutes and when it reaches the chuck it can spin out of control and cut your hands to ribbons.
Now, you can use a step drill and they are specifically designed for sheet metal and thin stock but what do you do if you want a hole that is a specific and non standard size, like a letter drill or number drill size.
The trick is to trap a couple of folds of soft cloth like cotton, or some other non synthetic cloth (not nylon) between the workpiece and the tip of the drill. Then just drill through the stock as you would normally. The cloth will keep the stock pushed down against the drill table and as the cut progresses, the cloth will pack into the flutes of the drill bit and keep it centred as the cutting edges break through.
This is not my idea. I first read about it in the Model Engineer Magazine many years ago but it works and it's simple.
Regards,
Preso
Check out the video for some examples of how well it works.