Every few weeks, someone asks me the same question: “Should I use a Bonfiglioli servo gearbox, or is a NEMA 23 stepper motor enough?”
I’m a quality/compliance manager at a power transmission service center. I review a lot of gearboxes—maybe 200 a year, give or take. In Q1 2024, I rejected 7% of first deliveries because the test paperwork didn’t match the actual backlash measurement. So when I compare these two options, I’m less interested in brand names and more interested in the numbers that affect your machine.
Honestly, comparing a gearbox to a motor is a bit apples-to-oranges. What people usually mean is the whole axis: a servo motor with a Bonfiglioli servo gearbox on one side, and a NEMA 23 stepper motor with a lead screw or reducer on the other. That’s the comparison I’ll make here. It took me about five years and a few hundred inspections to understand that the gearbox is usually where reliability is won or lost.
How I Frame the Comparison
I look at four things:
- Torque and speed behavior
- Backlash and repeatability
- Cost and complexity
- What happens when something goes wrong
If one of those is a deal-breaker for your application, the rest doesn’t matter.
Dimension One: Torque and Speed
A NEMA 23 stepper motor holds torque well at standstill. A typical NEMA 23 can produce around 1–3 Nm of holding torque depending on the motor length. That’s genuinely enough for a lot of point-to-point motion, especially at low speed with a lead screw.
But stepper torque drops off as speed increases. The faster you go, the less torque you get. This is physics, not a brand weakness.
With a Bonfiglioli servo gearbox, the situation is different. The servo motor keeps more torque across a wider speed range, and the gearbox multiplies it. At the output flange, a small servo motor with a 10:1 gear reducer can hold a load that a NEMA 23 stepper can’t touch at speed.
Now the part that surprises a lot of engineers: for slow, low duty-cycle movement, a NEMA 23 stepper motor is often enough. The “you must use servo” thinking comes from an era when steppers had low torque and no feedback. That’s changed. Closed-loop NEMA 23 steppers are real. But the fundamentals haven’t changed: if you need torque at high speed, you need a servo-class axis.
Dimension Two: Backlash and Repeatability
Backlash is the play between the input and output of a gearbox. When I inspect a Bonfiglioli servo gearbox, I measure backlash with a dial indicator and a torque arm. I want to see the number on the test sheet match the number on the actual unit.
Why does this matter? Because repeatability isn’t about rated resolution. It’s about how much the load moves when the motor reverses. A stepper with a loose gearbox will be less repeatable than a servo gearbox with low backlash.
A Bonfiglioli right angle gearbox is a good option when space is tight, but don’t assume it has the same backlash as an inline planetary. Right-angle reducers often have more backlash, and some have much more. Check the actual backlash number before you commit.
If you’re using a NEMA 23 stepper motor, you can avoid backlash problems by connecting directly to a lead screw. But with direct drive, the motor can only turn as fast as the screw allows. Add a reducer to a stepper and you gain torque but introduce backlash. There’s no free lunch.
Dimension Three: Cost, Complexity, and Support
A NEMA 23 stepper motor setup is cheap and simple. The driver is inexpensive, setup is short, and if it breaks, you swap it out.
A servo axis with a Bonfiglioli servo gearbox costs more upfront. You need the servo motor, the drive, tuning, and a gearbox with the right ratio and service factor. But for a machine that runs 24/7, the predictable support and replacement parts matter. Bonfiglioli has repair and spare parts channels that a generic stepper motor doesn’t.
There’s also a skills cost. A stepper system can be wired up by almost any machine builder. A servo axis needs someone who understands gain tuning, electronic gearing, and safety circuits. That’s not a reason to avoid servo, but it’s part of the real cost.
I’ve learned this the hard way. In 2023, we helped a customer replace eight gearboxes because the first supplier’s test data didn’t match the actual backlash. That was a $22,000 redo and a delayed launch. If you’re building a production machine, the lowest quoted price isn’t always the lowest total cost.
Don’t Forget the Linear Bearings
While you’re making this decision, don’t forget the parts that turn rotation into linear travel. The LM8LUU linear bearing is common in automation.
The question I see in online forums is: “what size is lm8luu linear bearing?” The LM8LUU is an 8 mm linear bushing—8 mm inner diameter, 15 mm outer diameter, and 24 mm long in the long version. It runs on an 8 mm shaft. The first 8 in the name is the shaft diameter. The 15 mm outer diameter matters if you’re designing the bearing mount, and the 24 mm length affects how much support you get on the shaft.
I mention this because a motor and gearbox are only as good as the bearing that carries the load. A misaligned linear bearing can bind, and that binding shows up as lost motion or missed steps on a NEMA 23 stepper motor. It also shows up as torque spikes on a Bonfiglioli servo gearbox.
What I’d Pick and Why
So which is better? It’s basically a trade-off between duty cycle and upfront cost.
Choose a NEMA 23 stepper motor if your axis is simple, the speed is low, the load doesn’t change much, and the machine isn’t running around the clock. It’s a practical, proven choice.
Choose a Bonfiglioli servo gearbox if you need fast cycles, high repeatability, varying loads, or long uptime. If space is tight, look at a Bonfiglioli right angle gearbox—but confirm the backlash rating before you commit.
What was best practice in 2020 may not apply in 2025. Steppers are better, servo drives are more accessible, and low-backlash reducers are more available than ever. But the parts that fail in the field are still the ones nobody checked: backlash, alignment, bolts, and documentation.
As a quality person, I’ll leave you with a small checklist. Ask for the backlash test report. Compare it to the catalog class. Confirm the ratio and the service factor. Check the shaft runout. If the paperwork doesn’t match the part, that’s a red flag—even with a well-known brand.
The gearbox is where reliability is won or lost. The motor gets the attention, but the reducer does the heavy lifting.