If the hole is more than 3 diameters deep, consider drill as much as twice as slow since it will be much harder for heat to escape.Drill bits are the most common accessory for drills.Cutting fluid will almost always increase the quality of the cut. Adding cooling / cutting fluid may allow speed increases, too, and should be used in any case on steels.If you’re using carbide tool bits, up the speeds by 2 to 3 times. If you’re using carbon steel drill bits (unlikely), cut the recommendations in half. HSS gets its name because it is able to maintain a reasonably hard cutting edge even while it is red hot. Note that these values are recommended for HSS (High Speed Steel) drill bits, not carbon steel ones.If the hardness is above 300 Brinnel, starting at 20-30 SFM isn’t a bad idea. If the material has been hardened, the recommended speed will be substantially lower.“First Guesses” are based on more typical materials and hardnesses.These numbers are more just for reference, it’s fine to go slower, just don’t push too hard on the small bits. First, note that the speed recommendations for small bits in aluminum are ridiculously high compared to the max speed of around 3000 RPMs on bench-top drill presses.Some considerations for using the above table: RPM recommendations based on First Guess Speeds Rotation Speed (RPMs) = (3.82) * SFM / Dia. So, the translation between SFM and the RPM speed of a drill bit is: On drill bits, the fastest cutting rate is at the circumference, and its rate of travel is equal to the RPM (Revolutions Per Minute) of the bit times the circumference (pi*Diameter). Surface Feet per Minute (SFM): Speed recommendations are usually given in SFM, which is the speed a cutter can be pushed in a straight line. Don’t push as hard right when the bit is about to break through, this will reduce the likelihood of it grabbing and tearing the metal. In general, push hard enough to create a continuous chip (note some materials just won’t form one–like cast iron), but not so hard that the chips are turning brown or the bit itself is chipping. This, of course, isn’t very useful if you’re lowering the drill bit by hand. 001″ per revolution for bits under 1/8th” to. For reference, the recommended rates go from. This ensures that too much metal isn’t chewed off too quickly.įeed Rate: This is how fast the drill bit is pushed down. A tip for drilling extremely small holes is to drill down to the depth stop, and then move it down a 16th of an inch, and repeat. Using recommended RPMs (spindle rotation speed) mitigates this risk. With small bits, it’s hard to feel resistance from the metal, and therefore, very easy to push down faster than they can remove metal. In general, a slower-than-recommended spindle speed won’t hurt anything except in the case of extremely small drill bits, say smaller than 1/16″. If the chips are smoking, turning brown, or the outer edge of the drill bit is chipping, go slower or add some cutting oil / coolant. (a decent guide to cutting fluid) Even if the material and its hardness were precisely known, the large number of other factors would require some experimentation. This is partly due to the large influence the material hardness has on how fast it can be drilled (harder –> slower). You’ll typically see large ranges of recommended speeds for various materials, and some discrepancy between different sources. So, for the hobbyists shop, where longer tool life is probably more important than machining time, and where pushing the speed limit may ruin a valuable prototype, reasonable advice might be to start off at about 75% of the recommended drilling speeds. The “First Guesses” below are already a little slower. The recommendations seek a balance between these two concerns, but this balance is not determined with the pocketbook of someone running a hobbyist or prototype shop in mind.

As drilling speed increases productivity goes up, but tooling also wears out faster. Also, most speed recommendations are geared towards manufacturing environments where machining time is very expensive. Going slower usually doesn’t hurt, and will prolong tool life.ĭrill press spindle speeds depend on lots of things: the type of material being drilled and its hardness, the hole size, the type / hardness of the drill bit and its sharpness, whether or not a cutting / cooling fluid is used, and the rigidity of the drill and clamp, among others. A 3/8″ drill bit drilling mild steel at the recommended speed and feed could require around 1 hp. In most cases the drill press will not be able to supply enough power or speed to follow the below recommendations. Quick Summary: Some approximate starting advice is to set the spindle speed between 700-1000 rpms for steel, above 2000 for aluminum, and slow down from there if you get discolored chips or heavy drill bit wear.

Drill bit size speed chart