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Drill

Torque = (Horsepower × 5252) / RPM

  • Some motors maintain torque better under load (especially capacitor-start induction motors or TEFC motors)
  • The WEN’s motor is lower quality — it bogs down easier under load
    • WEN 4214T uses a variable pulley system (belt + reeves drive). These lose torque at lower speeds.
    • basic capacitor-start, induction motor (capacitor-start split-phase induction motor (usually capacitor-start)
    • Better: electronic variable speed + geared belt drive or DC motors with constant torque curves maintain torque
      • Capacitor-start, capacitor-run induction motors, sometimes with TEFC (Totally Enclosed Fan Cooled) design
    • big Forstner bits that ideally run at 250–500 RPM.

Current drill I own - corded drill - amazon

  • Black and Decker
  • DR260C
  • 5.5 amps
  • 1600 rpm
  • corded
  • $45
  • 3/8in (10 mm) chuck

Jake's drill press

  • WEN 4214T
  • brushless, induction motor
  • 5-Amp
  • 12 inch swing
  • 3 1/8 inch spindle travel
  • 580 to 3200 RPM
  • 5/8-inch capacity keyed chuck
  • $220 home depot
  • 0.75 horsepower

Let’s say you’re using a 2" Forstner bit in hard maple:

  • Required torque to cut = ~6–10 Nm
  • WEN motor may produce ~3–4 Nm at 580 RPM

Purchase-able drill:

  • aliexpress cordless drill
    • Rated Input Power: 130W
    • Torque: 28 Nm
    • No-Load Speed: 1600rpm
    • Rated Voltage: 21V
    • Chuck: 3/8in
    • $26
  • Miwaulkee Impact Driver
    • $170
    • Recommended by Greg due to noise level
    • Used for tougher bolts
    • limitation: needs bits with hex collet (1/4")
      • many drillbits don't have a hex collet (spade, forstneer, even standard)
      • cant limit overdriving with torque limiter that drills have
        • but can work if u know ur impact driver well, generally not as smooth

Common Drill Motor Specs

Most common consumer-grade drills use motors like:

  • 775 DC Motor (commonly seen in 12V–24V drills)
  • Brushed, high RPM (~18,000 RPM no-load)
  • Geared down inside the drill to ~1200–1800 RPM at the chuck
  • Stall current: 15–60 A depending on voltage
  • Motor resistance: ~0.2–1.0 Ω depending on design

'''V=I⋅R, @ stall current'''

'''τ=Kt⋅I, Kt is torque constant'''

Speed vs Torque

High speed only makes job faster but doesn't really provide much else, and can be done with higher torque drills

  • Soft material, for quickness, use high speed
  • Hard material use higher torque

Drills generally have a gear 1 (high torque) or gear 2 (high speed) options

  • So at stall torque of gear 2, you a factor less than high torque of gear 1
  • aka: gear 2 has a lower mechanical advantage

When you increase the speed with no load, it stops spinning indefinately cause the back emf reduces operating voltage

  • back emf occurs due to motor spinning

If you change the operating torque, but not the speed in a drill, you are reducing the applied voltage to motor

Common Motors Used in Drills

1. Brushed DC Motors

Types:

  • 775 size motor (industrial standard)
  • 550 size motor (smaller, less powerful)

Typical Specs:

  • Voltage: 12 V to 24 V (cordless), up to ~120 V DC (corded, rectified)
  • No-load speed: ~15,000–20,000 RPM (motor shaft)
  • Geared down to ~1200–1800 RPM at chuck

Torque Constant (K_t):

  • Approximately 0.02 to 0.06 Nm/A
  • Higher power motors have lower (K_t) (higher speed, less torque per amp)

Motor Winding Resistance:

  • Ranges from 0.1 Ω to 1.0 Ω depending on size and voltage rating
  • Larger motors → lower resistance (~0.1–0.3 Ω)
  • Smaller motors → higher resistance (~0.5–1.0 Ω)

2. Brushless DC Motors (BLDC)

Types:

  • 3-phase brushless motors, custom windings for torque-speed profile

Typical Specs:

  • Voltage: 18 V to 60 V (common cordless tool batteries)
  • No-load speed: 20,000+ RPM (motor shaft)
  • Gear reduction to desired chuck speed

Torque Constant (K_t):

  • Typically 0.02 to 0.07 Nm/A
  • More efficient with better torque curves than brushed m

Motor Torque

  • A 550 motor drawing 5 A would produce around 0.2 Nm of torque.
Drill Type Voltage (Typical) Stall Torque Range (Nm) Notes
Corded Drills 110-120 V AC (rectified DC) 20 – 50 Nm Powerful, stable torque, heavier units
Cordless Drills 12 – 24 V DC (some up to 60V) 10 – 40 Nm Portable, often brushless, torque varies with battery voltage & model
Heavy-Duty Cordless 36 – 60 V DC 40 – 90 Nm High torque for professional tools
Compact Cordless 10.8 – 14.4 V DC 5 – 15 Nm Smaller, light-duty drills
Drill Type Typical Gear Ratio Range Notes
Corded Drills ~10:1 to 25:1 Heavy-duty motors spinning fast, geared down to provide high torque and lower speed at chuck
Cordless Drills ~15:1 to 30:1 Compact motors, often brushless, geared down to balance torque and battery efficiency
Heavy-Duty Cordless Up to 30:1 or higher For high torque applications, gearboxes provide strong torque multiplication
Compact Cordless ~10:1 to 20:1 Smaller gearboxes for lightweight drills, less torque multiplication
Current (A) 550 Motor Torque (Nm) (K_t=0.04) 775 Motor Torque (Nm) (K_t=0.06)
2 0.08 0.12
5 0.20 0.30
10 0.40 0.60
15 0.60 0.90
20 0.80 1.20

Stall Currents for 550 and 775 Motors

Stall current can be much higher than rated continuous current. A drill may briefly draw 15–30 A during stall or heavy load, increasing torque proportionally.

Motor Model Rated Voltage Terminal Resistance (Ω) Stall Current (A)
550 Motor 12V ~0.5 – 0.8 Ω 15 – 24 A
775 Motor 18V / 24V ~0.2 – 0.4 Ω 45 – 90 A

Larger gear ratios:

Reflected inertia grows with the square of the gear ratio:

  • J_reflected = J_load × (gear ratio)^2
  • T = J × α
  • P = T × ω

High inertia requires higher torque to overcome, so requires more current draw

  • may lead to running into stall current before accelerating, so no movement :(