Drilling Speeds and Feeds

Last week we talked about speeds and feeds in general.  Today we are going to focus specifically on drills.  Drills are one of the hardest working cutting tools. They remove more material relative to their size then any other cutting tool.  A reamer typically removes 2%-3% of its diameter; a core drill removes 30% of its diameter.  A twist drill removes 100% of its diameter.  As a result, feeds and speeds play a large role in the performance of a drill. Speeds and feeds change with the type of material being drilled (i.e. non-ferrous, cast iron, steel, etc.) as well as the hardness of the material being drilled. 

No matter what material you are drilling, the formulas remain the same:

RPM =    (SFPM*3.82)
            (TOOL DIAMETER)

IPM=IPT*RPM*#TEETH

IPR = IPM/RPM

Whether you use carbide tipped, solid carbide or HSS drills use the drill manufactures speeds and feed chart for surface foot per minute (SFPM) recommendations in the materials and hardness you intend to drill. Here is a link to a drilling speeds and feeds chart for carbide tipped drills.  There are two charts: one for drilling dry (no coolant) and one for drilling with coolant.

For drilling most materials (excluding steel and high temperature alloys) carbide tipped twist drills provide a high performance solution. The drilling speeds and feeds chart referenced above provides the appropriate SFPM and IPR for most common materials.  When drilling diameters less than 1/8”, solid carbide or high speed steel drill bits are recommended over carbide tipped drills. This is primarily due to the structural design of carbide tipped drills vs. solid carbide drills. Carbide tipped dills are typically a two piece construction involving slotting the end of a tool steel body and bonding a carbide tip into the slot. The drill is then sharpened to the design specifications. Drills less than 1/8” diameter do not provide enough mass to bond the carbide tip to the tool steel body. When drilling diameters less than 1/8” it is important to remember that the web of a small drill is thicker by ratio than the web of a larger diameter drill. The thicker web helps to prevent tool breakage in small diameter drills however requires that you retract or “peck” the drill more frequently to prevent the flutes from becoming clogged. Speeds and feeds for drilling small holes with solid carbide drills are calculated using the same formulas as above. Here are a few guidelines for SFPM with general purpose solid carbide twist drills between 1/16” and 1/8” diameter.

Low Carbon Steels <38HRc 100 – 175 SFPM, Feed 0.002 – 0.003 IPR

Examples: 1018, 12L14, 8620

Medium Carbon Steels <38HRc 100 – 150 SFPM, Feed 0.001 – 0.0015 IPR

Examples: 4140, 4340

For drilling hardened steel, stainless steels, and other hard and abrasive high strength materials up to 65 HRc we recommend using either a straight fluted carbide tipped or solid carbide die drill

If you are using a die drill (solid carbide or carbide tipped) 75 to 100 SFPM with a feed rate of 0.001 to 0.003 IPR is a good starting point.  Below are some tips for drilling steel with die drills.

1) Flood the point with coolant

2) Apply light feed with steady pressure withdraw frequently (peck) to clear chips

3) Select spade type drill for rigidity in short reach applications

4) For general purpose or when application specifications are vague, start with

    a 118º negative edge type die drill

Selecting the correct die drill can be a challenge as they come with different point angles (118° and 140°) as well as negative points and positive points.  Here is a link to a die drill selection chart.

Check back with us next week.  If you have any questions or comments about drilling speeds and feeds or any other cutting tools feel free to leave us a comment here on our blog or on Super Tool’s Contact Us Page.

Bryan Enander

Super Tool, Inc.

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  1. Jefrey Schmiedeck says:

    how do you calculate speeds and feeds for t max drills