Useful Trick

[kess]

An easy and useful trick when some times the standard numbers of drill bits (In my case Ø16 & Ø16.5mm) isn't suitable for our needs and the price of midrange numbers is too expensive to bay one and perhaps for only one time use.
I have use an Ø6mm aluminum pipe (because it was at front of me),
but a piece of an Ø6mm steel rod it is a better choice with longer life.
At the middle of the one edge I make a cut using my grinder with a cutting disk 1mm.
Then I passed through a strip of emery-cloth Num-150 and wrapped anticlockwise.