Drilling steel - How Fast and How Much Pressure?
Knowing how to drill steel is a skill only learned by doing. As one who has not reached any serious competency yet, this dialog confirmed my seat-of-the-pants experience…
DrDave:
Run the bit at a speed and pressure until just shy of smoking or turning blue.
Stan:
I think you have found the ideal speed from a lot of experience drilling holes. For an inexperienced person that is the equivalent of ‘tighten the bolt until it breaks and then back off a quarter turn’. If you don’t have some ballpark idea of the correct speed before you start, you either ruin a drill bit or make very slow progress.
Then getting serious, Stan adds:
Figure on 100 feet per minute cutting mild steel. Calculate the circumference of the bit in feet and divide by two (a bit has two cutting flutes) times the RPM of the drill. A few caculations will give you some idea of how fast to run your drill with different size bits.
And DrDave concludes:
If you are getting more than 20 holes on a bit, It’s a good Day!!
Huh. Tighten a bolt till it breaks then back off. What a comedian. 
