NEMA 17 vs NEMA 23 Stepper Motors: Pick the Right One for Your CNC
The question everyone asks: Will my NEMA 17 work for a bigger machine, or do I need to jump to NEMA 23? You've seen the forum posts. Someone runs a NEMA 17 on their 300mm DIY router. Someone else claims you'll strip gears on anything larger. The truth is messier and more interesting than either camp
Table of Contents
- What NEMA Actually Means
- NEMA 17 Specifications and Where It Works
- NEMA 23 Specifications and Real-World Use
- The Driver and Voltage Are Half the Equation
- Speed vs. Torque: The Curve That Kills You
- Unit Conversion (oz-in vs Nm)
- Stack Length and the Weight Penalty
- Machine Size and Ballscrew Pitch Guide
- NEMA 34: Almost Never Worth It
- Recommended Pairings by Application
- What We'd Buy
- Parts for this guide
- Related Articles
What NEMA Actually Means
NEMA frame size describes a mechanical size class, not torque. Check the motor drawing for the actual face, mounting holes and shaft dimensions.
- NEMA 17: commonly about 42 x 42 mm at the face; confirm the drawing.
- NEMA 23: commonly about 57 x 57 mm at the face; confirm the drawing.
Frame size leaves plenty unspecified: body length, winding, current, inductance and torque-speed performance. A larger frame can offer more torque, but compare actual motor models rather than predicting the result from face size or length alone.
NEMA 17 Specifications and Where It Works
One documented NEMA 17 example, StepperOnline's 17HS19-2004S1, has these specifications:
- Holding torque: 0.59 Nm (83.55 oz-in)
- Rated current: 2.0 A per phase
- Weight: 390 g
NEMA 17 is the sweet spot for:
- Compact machines whose required torque, speed and motor mounts suit the selected model
- Standard MPCNC Primo builds using V1's specified NEMA 17 motors, belt-driven X/Y and leadscrew Z
- Light-duty axes sized from their loads and transmission, rather than a fixed work-area limit
A low feed rate alone does not establish that a motor has enough torque. Account for cutting force, friction and acceleration. If an open-loop stepper loses steps, the controller's displayed position can become wrong; stop, resolve the cause and re-establish position before continuing. A stall is not a protective feature.
Rapids depend on the exact motor, driver voltage and current, acceleration, screw lead and moving load. Check the torque-speed curve and test with margin; NEMA 17 plus a 1605 screw has no universal maximum travel speed.
NEMA 23 Specifications and Real-World Use
One documented NEMA 23 example, StepperOnline's 23HS22-2804S, has these specifications:
- Holding torque: 1.24 Nm (175.6 oz-in), as listed in the current detailed specification
- Rated current: 2.8 A per phase
- Weight: 700 g
- Body length: 56 mm for this model; other NEMA 23 models have different lengths, windings and torque-speed curves.
NEMA 23 is the standard for:
- Axes whose torque-speed requirement exceeds what the chosen smaller motor can provide
- Repeated cutting work where the selected motor has adequate torque and thermal margin; motor size does not make unattended cutting safe
- Aluminum cutting where you need the torque reserve
- Gantry-style machines where the Y-axis carries significant weight
The useful advantage is torque available at the required speed, not frame size alone. Check a named motor's curve with the intended driver and supply. A 76 mm body and a 2005 screw do not establish a reliable rapid rate.
The Driver and Voltage Are Half the Equation
Here's where forum advice falls apart: people compare NEMA sizes without mentioning the driver.
A NEMA 23 on a 24 V driver must be assessed using that motor's torque-speed curve and the driver's current setting.
A NEMA 17 on a DM542T may gain usable high-speed torque with a suitable higher supply voltage, but resonance and torque still depend on the complete setup.
Compare torque at the required operating speed with the intended motor, driver and supply. Driver quality matters, but those two unspecified combinations do not establish a winner.
Good drivers for hobby use:
- DM542T and DM556T: Check the revision. StepperOnline V4 manuals specify maxima of 4.5 A peak and 5.6 A peak respectively, both with a 50 V DC ceiling. Allow supply tolerance and regeneration margin below that limit.
- Higher-voltage drivers: Select a documented model with suitable voltage, phase-current and signal-input ratings; a larger voltage rating is not itself a smoothness guarantee.
- TB6600-based modules: Check the actual module's manual, current setting and cooling; the label alone does not establish noise or vibration performance.
Rule of thumb: Choose driver voltage within the driver's limits, then compare the motor's torque-speed performance at that supply and current. Higher voltage can help current rise at speed, but does not make every NEMA 17 outperform every NEMA 23.
Speed vs. Torque: The Curve That Kills You
Stepper torque isn't constant. It drops as step frequency increases. This is published on motor datasheets, but most people ignore it.
At a chosen operating speed, compare the two motors under documented conditions:
- NEMA 17: use the selected motor's torque-speed curve
- NEMA 23: use the selected motor's torque-speed curve
Compare available running torque with the load and acceleration torque, with a suitable margin. Holding torque and frame size alone cannot tell you whether an axis will stall.
Unit Conversion (oz-in vs Nm)
The hobbyist community can't agree on units. Here's the conversion:
1 Nm = 141.6 oz-in
So that NEMA 17 at 0.7 Nm = ~99 oz-in. NEMA 23 at 2.5 Nm = ~354 oz-in. Flipping between datasheets is annoying, but the math is simple.
Stack Length and the Weight Penalty
These are three StepperOnline NEMA 23 examples, not three standardized lengths. Body length is not the same as internal stack length, and the torque figures below are holding torque. Use the current detailed specification for the exact model.
| Model and body length | Typical Torque | Weight | Inductance | Best For |
|---|---|---|---|---|
| 23HS22-2804S, 56 mm | ~1.2 Nm | 700 g | 2.68 mH | Compact mounting; check running torque |
| 23HS30-2804S, 76.5 mm | 2.00 Nm | Confirm the supplied motor's datasheet | 4.36 mH | Balanced builds |
| 23HS45-4204S, 113 mm | 3.00 Nm | 1600 g | 3.4 mH | Higher holding torque; check running torque |
A longer active motor stack can increase torque without adding rotor teeth or changing step angle. Inductance also depends on the winding: these examples do not increase monotonically with body length. Choose from the torque-speed curve and mounting constraints, not a universal 76 mm sweet spot.
For a vertical axis, include gravity, acceleration, screw lead and all moving mass in the torque calculation. Motor weight only adds to the lifted load if the motor moves with that axis; its rotor inertia matters even when the housing stays fixed.
Machine Size and Ballscrew Pitch Guide
Use this table as a set of checks, not a sizing rule based on work area. Required torque, speed, inertia and transmission details determine the motor and driver.
| Machine Size | Ballscrew | Motor | Driver | Notes |
|---|---|---|---|---|
| Compact machine or retrofit | Follow the machine's drive specification | Check torque at target speed | Match motor current and controller signals | Size alone does not determine cutting materials |
| MPCNC Primo, standard configuration | Belt-driven X/Y; leadscrew Z | NEMA 17 per the V1 build specification | Follow the selected V1 controller's supply limit | Follow V1's build and use guidance |
| 600–800mm (DIY router) | Select lead for required speed and force | NEMA 23 candidate; verify torque curve | Stay within the selected driver's supply limits | Check friction, inertia and acceleration |
| 800–1200mm (production) | Check screw speed and support arrangement | Select from torque, speed and inertia | Voltage and current within driver ratings | Steel construction alone does not set motor size |
| Over 1200mm or dual gantry | Select a drive suitable for the span and load | Select from torque, speed and inertia | Match driver to motor and supply requirements | Check synchronization if both sides are driven |
NEMA 34: Almost Never Worth It
NEMA 34 covers a wide range of motors. Consider one when the required torque and inertia justify the larger package, and compare actual models rather than treating all of them as one specification. Check:
- Actual motor mass, mounting dimensions and rotor inertia
- Rated phase current, suitable driver and calculated supply demand
- Winding inductance and the torque-speed curve at the intended supply
- Cost $80–150 per motor
NEMA 34 can be useful when the load, speed and inertia call for it, but a larger motor also changes cost, mounting and acceleration requirements. Select it from the axis calculation rather than a fixed 1500 mm machine-size threshold.
Recommended Pairings by Application
Example compact-axis components, subject to torque-speed and mounting checks:
- Motor: NEMA 17 (StepperOnline 17HS19-2004S1)
- Ballscrew: 1605 (pitch 5mm)
- Driver: TB6600 at 24V
- Budget: ~$60 total 3-axis
Example NEMA 23 axis components, subject to the machine's load and speed requirements:
- Motor: NEMA 23, for example StepperOnline 23HS30-2804S with a 76.5 mm body and 2.00 Nm listed holding torque
- Ballscrew: 2005 (pitch 5mm)
- Driver: DM542T with current matched to the motor and a supply that remains below its 50 V DC maximum, including tolerance and regeneration
- Budget: ~$120 total 3-axis
Large machines, heavy gantries (over 800mm):
- Motor: Select a specific NEMA 23 or NEMA 34 model from the torque-speed and inertia calculation
- Ballscrew: 2505 or 2010 depending on speed vs torque priority
- Driver: A suitably rated higher-voltage model if the motor requires it; the DM542T must not be run at 80 V because its maximum is 50 V DC
- Budget: ~$200–300 total 3-axis
What We'd Buy
A NEMA 23 with a suitable digital driver can be a practical choice for a hobby router, but check the exact motor's running torque, phase current and mounting. For a DM542T, keep the supply within its limits with headroom for transients. Choose components from the machine requirements rather than assuming one pairing suits nearly everyone.
Choose body length and winding from the required torque-speed performance and available space. Compare actual motor masses; a 76 mm-class motor does not carry a universal 100 g penalty or guarantee a better axis.
Parts for this guide
If you are buying after reading this, these are the specs to look for.
| Part | What to buy | Where to look |
|---|---|---|
| Compact NEMA 17 stepper A common NEMA 17 with a published datasheet. | StepperOnline 17HS19-2004S1: bipolar four-wire, 1.8-degree step, 0.59 Nm holding torque, 2.0 A/phase, 42 x 42 x 48 mm body and 5 mm shaft; verify the torque curve and wiring. | |
| NEMA 23 stepper with longer body A long-body NEMA 23 with a published datasheet. | StepperOnline 23HS30-2804S: bipolar four-wire, 1.8-degree step, current detailed specification 2.00 Nm holding torque, 2.8 A/phase, 76.5 mm body and 6.35 mm shaft; confirm the delivered revision. | |
| External digital stepper driver A driver matched to these motors' current and voltage. | StepperOnline DM542T V4.0: 18-50 V DC, up to 4.5 A peak/3.2 A RMS; match the current setting to the motor, leave bus-voltage headroom and set the signal-voltage selector for the controller. |
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