Planetary vs Worm Gearbox: Which One Fits Your Application?

How Each Gearbox Type Works

A planetary gearbox uses a central sun gear, a set of planet gears orbiting around it, and a fixed outer ring gear. Load is distributed simultaneously across all planet gears — typically three or four. This is why planetary designs achieve high torque in a small housing: multiple gear meshes share the load rather than a single contact point carrying it all.

A worm gearbox uses a helical worm screw driving a worm wheel at 90°. The contact is a sliding action — the worm tooth slides across the wheel face rather than rolling. This sliding generates heat, which is why worm gearboxes run hot and why their efficiency drops sharply as the ratio increases. At a 40:1 ratio, a worm gearbox commonly delivers 60–75% efficiency. A planetary gearbox at the same ratio typically delivers 96–98%.

The self-locking behaviour of worm gearboxes — where back-driving is resisted by the gear geometry — is often cited as an advantage. This is true for applications requiring a mechanical hold without a separate brake. But this same geometry is responsible for the efficiency loss, because any friction that prevents back-driving also dissipates forward-driving energy as heat.

Head-to-Head Comparison: The Numbers That Matter

The Energy Cost Argument — What the Numbers Actually Show

The worm gearbox is cheaper to buy. The planetary gearbox is cheaper to run. The crossover point depends on your annual operating hours and motor size. Here is a worked example:

For motors above 5 kW running more than 2,000 hours per year, the planetary gearbox is the lower-cost option over a 3-year horizon in the vast majority of cases. The worm gearbox only wins on total cost of ownership for low-duty, low-power, or intermittent applications where the self-locking property is genuinely needed and a separate brake is not viable.

When to Use a Planetary Gearbox

• Continuous-duty drives — conveyors, mixers, agitators, clarifier rakes running thousands of hours annually
• Applications where space and weight matter — mobile equipment, wheel drives, track drives, feed mixer wagons
• High gear ratios with maintained efficiency — multi-stage planetary achieves 5,000:1 without the steep efficiency cliff of worm designs
• Coaxial motor-to-load layout — when the motor axis must align with the load shaft
• OEM equipment design — where long service life and predictable maintenance intervals are a product specification, not an afterthought

When a Worm Gearbox Remains the Right Choice

• Self-locking is genuinely required and a separate brake cannot be added — lifting gates, hand-operated equipment, gravity-loaded positioning without electrical hold
• Very low-duty, low-power applications — infrequent use where efficiency loss is financially irrelevant
• 90° output is needed on an extremely tight budget — though a right-angle planetary gearbox with bevel stage is now competitive on total cost for any continuous-duty application

Replacing a Worm Gearbox with a Planetary Unit

If you are replacing an existing worm gearbox on a running machine, there are three things to verify before ordering a planetary replacement:

1. Output shaft angle: Worm gearboxes deliver 90° output. If you need to maintain that shaft direction, specify a right-angle planetary gearbox (bevel output stage), not an inline unit.
2. Self-locking requirement: If the worm’s self-locking behaviour is serving as the machine’s only hold against back-driving loads, you must add a hydraulic or electric brake to the planetary unit. This is standard — most planetary series offer an integral brake option.
3. Mounting footprint: A planetary gearbox at the same torque rating will be physically smaller than the worm unit. Confirm the output shaft diameter and mounting bolt pattern match or budget for a mounting adaptor.

For most industrial conveyor, mixer, and agitator replacements, an inline planetary gearbox with an IEC motor adaptor is a direct-mount drop-in, requiring only confirmation of shaft size and torque rating before ordering.

Summary: Which to Choose

If you’re evaluating a replacement or new specification, our engineering team can cross-reference your existing worm unit and recommend the correct planetary equivalent — including inline or right-angle configuration, IEC or hydraulic motor interface, and brake option if required. Send your requirements to [email protected] and receive a formal quotation within 24 hours.