There's a question I get almost weekly, usually from someone deep in a project with no time to spare: "Which Bonfiglioli gearbox do I need?" My answer always sounds like a dodge, but it isn't—it depends on what you're trying to do.
I say that as a quality manager who reviews gearbox configurations before they ship—roughly 200 units a year, maybe 180 in a lighter year, I'd have to check the log. In 2024 I rejected about 6% of first deliveries. 6.2%, if I'm being precise. I'm a quality guy; precision is kind of the job. The units weren't broken—the selection was wrong for the application.
So let's walk through four common scenarios. Find the one that matches your project, and you'll have a better sense of what to buy—and what to avoid.
Scenario A: You need precise positioning at speed
If your machine has to move fast, stop on a dime, and repeat that cycle thousands of times a day, you're in servo territory. That's where the Bonfiglioli servo gearbox range comes in. These are gear units built for the high dynamics of servo motors—low backlash to keep positioning accurate, and high torsional stiffness so the motor's motion actually reaches the load without twisting the gearbox.
Backlash is the play between gear teeth when the direction changes. It's measured in arcminutes—one arcminute is 1/60th of a degree. That sounds tiny, and in many applications it's fine. In a servo application running at high cycle rates, it's the difference between nailing the position and constantly chasing small errors.
Here's a story from our shop. When I implemented our verification protocol in 2022, we started checking servo gearbox backlash at three positions around the output flange. Two positions were fine. The third was off by four arcminutes. The assembler wasn't seating the bearing properly. If we'd only measured one spot, that unit would have shipped, and someone's robot arm would have had a repeatability problem that no software tuning could fix.
The gearbox is usually the reliable part of the equation, though. Servo motor wiring is where I see more issues. Encoder cables pick up interference from power cables if they're routed too close. Ground loops cause random position errors. A single swapped wire can damage a drive.
I still kick myself for approving a prototype layout years ago where the encoder cable ran parallel to the motor leads for about two feet. We chased intermittent faults for three weeks before someone finally separated the cables. That one cost us a $22,000 delay. Now every project review includes a cable routing checklist. If your servo system misbehaves, check the wiring before you blame the gearbox.
Scenario B: You need high torque at low speed
Planetary gearboxes are the classic workhorses here. Multiple planet gears share the load around the sun gear, which gives you a lot of torque capacity in a compact package. Bonfiglioli's planetary range covers everything from small servo-mounted units to heavy-duty drives for track drives and mobile equipment.
This is where I run into one of the most persistent misconceptions in the industry: people think planetary gearboxes are always better than worm gearboxes, because planetary is more efficient. That's true—planetary units can hit 95-97% efficiency per stage, while worm gearboxes run lower depending on ratio and speed.
But efficiency isn't the only thing that matters. A worm gearbox is self-locking in many configurations—the load can't push backwards through the gears when the motor stops. If you're building a lifting mechanism or a linear actuator, a worm gearbox can hold the load without a brake. A planetary gearbox won't.
So there's no universal winner. I've seen engineers install a planetary gearbox plus a brake on a vertical axis when a worm gearbox alone would have done the job, at lower cost and with fewer parts to fail. Efficiency is valuable, but it's not the whole story.
Scenario C: You need to turn power 90 degrees
When the drivetrain needs a corner, you're looking at a right-angle gearbox, and the spiral bevel gear is the standard for a reason. The teeth engage gradually rather than slamming together all at once, so spiral bevel drives run quieter, vibrate less, and handle shock loads better than straight bevel gears.
You'll find spiral bevel gearboxes in conveyor drive systems, packaging machines, and material handling equipment—applications where space is tight and smooth operation matters.
The critical detail with bevel gears is the tooth contact pattern. If the mesh between the pinion and the gear isn't positioned correctly on the tooth flank, the gear will fail early—no ambiguity about it. This is where I made one of my first mistakes as an inspector. I approved a first-article bevel set without checking the contact pattern under load. It looked fine at rest, but under torque the contact patch rode up to the edge of the tooth. We caught it during field testing and replaced the set, but it taught me a lesson I've never forgotten: for bevel gears, the pattern is the spec.
When you buy a spiral bevel gearbox, ask for the inspection report. If the supplier can't produce one, that's a sign.
Scenario D: You're just starting out and need a simple answer
Let me answer a question that comes up constantly: what's a stepper motor?
A stepper motor moves in discrete steps. Send a certain number of pulses to the drive, and the motor rotates that many steps—no encoder needed, because the drive simply counts the pulses. It's the simplest, cheapest way to do open-loop positioning.
Steppers make a lot of sense for indexing, feeding, and slow positioning tasks. And here's the part that's counterintuitive: a stepper paired with a well-matched gearbox can outperform a budget servo system at low speeds. The components are less expensive, the system is easier to commission, and nobody has to tune a servo loop. If your application moves slowly and the load is predictable, stepper is worth a serious look before you jump to servo.
The advice I give most often: size a stepper for torque at your operating speed, not the holding torque at zero speed. That's where most misapplications happen.
Steppers do have limits. Torque drops as speed climbs, they draw current at standstill if you leave the hold on, and if the motor misses a step, the system has no way of knowing. So they shine with modest speeds and consistent loads, not with aggressive, high-speed motion.
How to decide which scenario you're in
Here's the framework I use when engineers ask me for guidance. It's not fancy, but it covers the majority of applications:
- Need precise positioning at speed? → Servo plus a low-backlash gearbox.
- Need slow, accurate indexing on a budget? → Stepper plus gearbox.
- Need high torque in a small space? → Planetary gearbox.
- Need a right-angle output? → Spiral bevel gearbox.
Then ask yourself how much complexity you want to manage. Servo systems deliver excellent performance, but they come with more components—drive, motor, feedback cable, controller—and more places to fail. A stepper with a gearbox is simpler to get running. A conventional geared motor is even simpler.
One more thing. People sometimes assume that an expensive gearbox is reliable because it's expensive. That's backwards. A gearbox that's designed, assembled, and inspected correctly can charge more because it's reliable. The price follows the quality, it doesn't create it. When you choose a supplier, look at what their quality process looks like, not just the price tag.
And when you're ready to buy, you can shop Bonfiglioli's official range online to see standard gearboxes, motors, and spare parts. For anything unusual—extreme temperatures, high shock loads, a duty cycle that feels off—talk to an application engineer instead of basing a decision on a website. A wrong selection is the most expensive part you'll never see on the bill of materials.
Prices and specs change, so verify current ratings on the official product pages before committing. And if a quote looks too good to be true, ask why. In my experience, the gap between quotes shows up later—in the backlash reading, in the tooth contact report, or in the repair bay eighteen months down the road.