As a practical matter, how important are RPMs for drilling aluminum?
Someone suggested that aluminum likes high speed drills. More correctly we might say that small bits like high speeds. The cutting edge on #30 bit is making a much slower speed over the aluminum than that of a 1/2 inch bit. The larger the bit the slower you need to turn it. Slow way down for the fly cutter!
Generally, the harder the material, the slower the speed of the edge needs to be. Here are a few speed recommendations from an old handbook:
| Annealed 4340 steel | 60 fpm |
| Stainless 410 | 30 fpm |
| Aluminum alloys | 250 fpm |
Also, the recommended coolant for aluminum is water based solutions. (Milk?) I believe many who complain of non-round holes are feeding too fast. Feed (pushing the drill into the work) is given in inches per revolution. If one pushes a slow drill as hard as a fast one, the feed will be faster. Feed for aluminum should be 0.007 ipr, and steels about one fourth that.
[Drilling RPM can be determined from the cutting speed for the material and the diameter of the drill:
N =12xV/PIxDwhere N is the drill motor speed in RPM, and V is the cutting speed of the material in fpm. Using values from Machinery’s Handbook, the correct RPM for drilling a #30 hole in aluminum is:
N= (12 x 500) / (0.1285 x PI)which works out to 14,800 RPM! Clearly, you’re not going to exceed the recommended drilling speed with a hand drill. This emphasizes the importance of Hal’s advice to not feed the drill into the work too fast—Webmaster.]
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