Drilling Torque and Power Calculator
Large drills and small machines are a bad mix, and a drill that stalls usually breaks. This calculator gives spindle speed, programmed feed, torque and power for a drilling operation so you can check the machine before the cycle starts.
Your numbers
Your results
Approximation using average specific cutting force. Chisel edge thrust and web thickness are not modelled; confirm with your drill maker's data.
Drilling torque vs drill diameter
Sweeps Drill diameter from 3 to 40, holding your other inputs fixed.
Put machining parameters into ERP routings
Optional: talk to us about structured speeds and feeds data in your routing records.
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How to use it
Enter drill diameter, the cutting speed recommended for your material and coating, feed per revolution and a material group. The page returns rpm, the feed rate in mm/min, metal removal rate, power and torque. Compare the torque with your spindle curve at that rpm. Use the chart to see how fast torque grows with diameter, since it rises with the square of diameter at constant feed.
- Recommended feed per rev for twist drills is roughly 0.01 to 0.02 x diameter.
- Reduce speed 20 to 30 percent for deep holes beyond 5 x D.
- Carbide indexable drills usually run much higher speed than HSS.
Formulas
Spindle speed is n = 1,000 x vc / (pi x D). Feed rate is vf = f x n. Metal removal rate is pi x D squared / 4 x vf / 1,000 in cm3/min, power is Pc = MRR x kc / 60,000 in kW, and torque simplifies to T = kc x f x D squared / 8,000 in N-m with D in mm. The torque shortcut and the power-based torque agree, which gives a quick sanity check on your inputs.
Worked example
A 12 mm drill in carbon steel at 80 m/min and 0.15 mm/rev runs at about 2,122 rpm and feeds 318 mm/min. Metal removal is about 36 cm3/min, giving 1.2 kW at the cut or 1.5 kW at the motor, with 5.4 N-m of torque. A small machine with 2.2 kW but little torque at 2,000 rpm handles it. Move to a 30 mm drill at the same feed and torque rises about six times, so check carefully.
Common mistakes
The usual errors are using diameter in inches against mm formulas, forgetting that rpm falls as diameter rises so a large drill sits in a low-torque speed range, and ignoring thrust. Chisel edge thrust can exceed spindle or fixture capacity on thin parts even when power is fine. Pecking and coolant-through delivery matter more for deep holes than for any speed adjustment.
- Check the machine torque at the actual rpm.
- Use through-coolant for holes deeper than 3 x D.
- Pilot a large drill with a smaller one to cut chisel thrust.
Frequently Asked Questions
How do I get drill feed rate in mm/min?
Multiply feed per revolution by spindle rpm. For a 12 mm drill at 2,122 rpm and 0.15 mm/rev, feed rate is about 318 mm/min. This is the F value in G94 feed per minute mode.
What material value should I choose?
Pick the group closest to your material. If you have a tool maker's kc1.1 value, use that instead. The result scales directly with kc, so a 10 percent error in kc gives a 10 percent error in power.
Does drilling torque include thrust?
No. This estimates cutting torque only. Thrust force depends on chisel edge width, point angle and web thickness. Check the manufacturer data when drilling thin plates or on lightly built machines.
Why does torque matter more than power?
Large drills run at low rpm where a spindle may deliver only a fraction of its rated power. Torque tells you if the drive can turn the drill at that rpm without stalling.
If cycle times for drilling operations feed your standard costs, Netray can help automate pulling those parameters into ERP routings.
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