DRILL SPEEDS for Inch Drills, Metric Drills, Number Drills, Letter Drills:
General recommendations for speeds to be used when drilling various types of materials. If in doubt, it is advisable to start at the lower end of the speed range, and note the results of increasing drill speed until the life of the tool begins to decrease. Rigid machines of modern design can usually be expected to operate at rather higher drilling speeds than older machines in poor condition.
For Taper Pin Drilling, speeds and feeds should be between 40% and 50% of those recommended for a parallel drill equal to the large diameter of the taper drill. The amount of work required of a taper drill is ver considerable and this should be considered in all taper designs.
The speeds shown are given in surface feet per minute (ft/min) or surface meters per minute (m/min), measured at the periphery of thedrill. To calculate thedrill revolutions per minute (RPM) from the surface speeds, the following formulae should be used, where D=diameter of drill
RPM = Surface Ft/min x 12 divided by D inch x 3.14
RPM = Surface m/min x 1000 divided by D mm x 3.14