DRILL FEEDS and SPEEDS
"Different drilling conditions make it impossible to develop any rigid rules for feeds and speeds."
The following tables contain guidelines which can be utilized when drilling standard materials. Also, the following “rules of thumb” can be used to determine proper feeds and speeds for drilling ferrous materials.
(NOTE: varying conditions can easily require adjustments ).
• Feed equals: .001" per revolution for every 1/16" of drill diameter, plus or minus .001" on the total.
• Speed equals: 80 surface feet per minute in 100 Brinell hardness material and the speed should be reduced 10 surface feet per minute for each additional 50 points Brinell hardness.
• Feed and speed rates: should be reduced up to 45-50‰ when drilling holes deeper than 4 drill diameters.
Feeds and Speeds - Formulas
R.P.M. = (3.8197 / Drill Diameter) x S.F.M.
S.F.M. = 0.2618 x Drill Diameter x R.P.M.
I.P.M. = I.P.R. (feed) x R.P.M. (speed)
Machine Time (seconds) = (60 x Feed minus Stroke) / I.P.M.
R.P.M. = Revolutions Per Minute I.P.R. = Inches Per Revolution
S.F.M. = Surface Feet Per Minute Feed Stroke = Drill Depth + 1/3
I.P.M. = Inches Per Minute Car Reamer = 1/2 Speed of Drill
S.F.M. = 0.2618 x Drill Diameter x R.P.M.
I.P.M. = I.P.R. (feed) x R.P.M. (speed)
Machine Time (seconds) = (60 x Feed minus Stroke) / I.P.M.
R.P.M. = Revolutions Per Minute I.P.R. = Inches Per Revolution
S.F.M. = Surface Feet Per Minute Feed Stroke = Drill Depth + 1/3
I.P.M. = Inches Per Minute Car Reamer = 1/2 Speed of Drill
Recommended Feeds of Various Diameter Drills
| Diameter of Drill - Inches | Feed Inches per Revolution |
| Under 1/8 | .001 to .003 |
| 1/8 to 1/4 | .002 to .006 |
| 1/4 to 1/2 | .004 to .010 |
| 1/2 to 1 inch | .007 to .015 |
| 1 inch and over | .015 to .025 |
Typical Brinell Hardness Numbers for Metals
| Materials | Hardness Number |
| Soft brass | 60 |
| Mild Steel | 130 |
| Annealed Chissel Steel | 235 |
| White Cast Iron | 415 |
| Nitrided Surface | 750 |
Recommended Speeds for Standard Materials
with High Speed Steel Drills
| Material | Recommended speed (SFM) |
| Aluminum and its Alloys | 200-300 |
| Brass and Bronze (Ordinary) | 150-300 |
| Bronze (High Tensile) | 70-150 |
| Die Casting (Zinc Base) | 300-400 |
| Iron-Cast (Soft) Cast (Medium Hard) Hard Chilled Malleable |
75-125 50-100 10-20 80-90 |
| Magnesium and its Alloys | 250-400 |
| Monel Metal or High-Nickel Steel, Stainless Steel | 30-50 |
| Plastics or Similar Materials | 100-300 |
| Steel Mild .2 Carbon to .3 Carbon Steel .4 Carbon to .5 Carbon Tool 1.2 Carbon Forgings Alloy - 300 to 400 Brinell |
80-110 70-80 50-60 40-50 20-30 |
| High Tensile (Heat Treated) | (Consult your Material Supplier) |