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Servo or Stepper Motor For a Hollow Rotary Table? Which one you shall select?

Picking the wrong motor for a hollow rotary table is one of those mistakes that doesn't announce itself on day one. The machine runs, the table rotates, everything looks fine — until a fixture is slightly heavier than the last one, or the cycle rate gets pushed during a production ramp-up, or a table that's been running for six months starts missing positions. By that point, the cost of the wrong decision has already compounded. The motor drives the whole system. It determines how accurately the table indexes, how smoothly it rotates, how it behaves when the load changes, and whether it holds up through years of production. The hollow bore — the feature that makes this style of rotary table so useful for routing cables, pneumatics, and optical paths through the rotational axis — does not change the motor selection logic, but the applications that typically use hollow rotary tables do. Here is a clear-eyed breakdown of Servo or Stepper Motor For a Hollow Rotary Table.

Understanding the Drive Architecture First to Select A Servo or Stepper Motor For a Hollow Rotary Table

Most hollow rotary tables reach the market in two broad configurations, and the motor pairing logic is different for each. The first is a geared hollow rotary table, where a gear set, a planetary gearbox, or a hypoid gear reduces the motor speed and multiplies its torque before reaching the table output flange. Reduction ratios of 50:1, 100:1, and higher are common. The gear train introduces mechanical advantage, reduces the reflected inertia the motor sees, and — in the case of worm gears — provides self-locking behavior. The second is a direct-drive hollow rotary table, where a frameless torque motor is integrated concentrically into the table body. The motor rotor bonds to the output flange directly; there is no intermediate gear set. All positioning accuracy comes from closed-loop control and a high-resolution encoder mounted at the output. These tables are always servo-driven — there is no viable stepper option in a direct-drive architecture. The decision between servo and stepper is therefore most relevant for geared hollow rotary tables, and that is where the real-world selection question lives for most engineers and machine builders.

When Stepper Motors Make Sense

Stepper motors are a legitimate, well-proven choice for geared hollow rotary tables in the right operating conditions. The key is understanding where those conditions begin and end. Indexing Cycles with Defined Positions by stepper motor The application profile that suits stepper motors best is straightforward: the table advances to a fixed angular position, dwells while work is performed, then advances again. This is the classic rotary indexing pattern — welding stations, assembly fixtures, inspection carousels, multi-station transfer units. In this profile, speed is secondary. The move happens, the table locks, the dwell absorbs most of the cycle time. A stepper motor driving through a worm gear reduction handles this reliably. Each commanded step translates into a precise angular increment at the motor shaft, and the gear reduction compounds that resolution at the table output. Running a 200-step motor with 1/16 microstepping through a 100:1 worm drive gives angular resolution at the table that is finer than most application tolerances require. The worm gear's self-locking characteristic is worth calling out specifically. At the ratios common in hollow rotary table drives, the gear cannot be back-driven. When the motor reaches the commanded position, the table is mechanically locked — no holding current, no active brake, no servo stiffness needed. For fixtures clamping workpieces during machining or pressing operations, this is a real operational advantage. Light-to-Moderate, Consistent Payloads by stepper motors Stepper systems operate open-loop. The controller sends pulses; the motor is expected to follow. This works reliably when the load on the table is well-characterized, consistent between cycles, and sized with appropriate torque margin. The danger zone is variable or unpredictable loading. A table that occasionally receives heavier fixtures, or one where an operator might load a part off-center, creates load conditions outside what the motor was sized for. In open-loop operation, that condition produces a missed step — and the controller has no way to know it happened. The table is at the wrong angle; the machine continues running. For applications where the fixture weight and balance are controlled and repeatable, this risk is manageable. For applications with genuine variability, it is not. Cost-Driven Projects with Modest Performance Requirements by stepper motors There is no point pretending otherwise: stepper motor and driver combinations cost significantly less than servo systems of equivalent frame size. For OEM products built to a price point, laboratory instruments with light-duty cycles, or machines where the rotary axis is genuinely not the performance-critical element, the cost difference is a real factor. A stepper-driven hollow rotary table that is correctly sized, operated within its performance envelope, and paired with a worm gear drive will run reliably for years. Plenty of successful production equipment is built exactly this way.

When Servo Motors Are the Right Choice

The servo motor's closed-loop architecture — continuous position feedback, real-time error correction, active torque management — handles the conditions where stepper systems run out of capability. Variable or Unpredictable Loads by servo motors When the payload on the table changes between cycles, servo motors adapt automatically. The drive detects positional deviation from the encoder and applies corrective current instantly. Whether the table is carrying a 2 kg fixture or a 12 kg assembly, the servo drive responds to what the load actually is — not what the sizing calculation assumed it would be. In flexible manufacturing cells, multi-product assembly lines, and automated handling systems where different parts share the same rotary station, this adaptive behavior is not a luxury. It is what keeps the machine running without babysitting. High Throughput and Aggressive Cycle Times by servo motors Faster index cycles demand faster acceleration and deceleration. Stepper motors produce maximum torque at low speeds and lose torque progressively as speed rises — precisely where aggressive acceleration profiles need it most. Servo motors deliver peak torque (typically three to five times their continuous rating) during acceleration, then settle to continuous torque during constant-speed rotation. This characteristic is what makes tight cycle times achievable. When production throughput is the design driver — parts per hour targets that require sub-second index moves — servo-driven rotary tables are the tool for the job. Angular Accuracy Tighter Than Open-Loop Can Deliver Worm gear drives have backlash. Open-loop stepper control cannot correct for it. For most indexing applications, this is not a problem — the backlash is small, consistent, and absorbed into the system tolerance stack. But when angular positioning accuracy at the table output needs to be ±0.01° or better — precision welding fixtures, optical component alignment, sensor calibration rigs, five-axis machine tool rotary axes — closed-loop servo control with a quality encoder at the output is required. The servo drive eliminates backlash error by commanding to the measured output position, not to the assumed motor position. At the extreme end, direct-drive torque motor tables with output encoders measuring to arc-second resolution are used in semiconductor handling, precision laser processing, and medical imaging equipment. These are always servo systems, without exception. Continuous Rotation Applications Not every hollow rotary table application is index-and-dwell. Antenna positioning systems, inspection turntables, camera pan platforms, laser beam steering units, and certain test rigs require smooth continuous rotation at controlled velocity. Stepper motors in continuous rotation generate audible noise at step frequencies, produce velocity ripple that translates directly into angular instability, and offer no mechanism for maintaining commanded speed under load variation. Servo motors run smoothly at any commanded speed, maintain velocity under changing loads, and can execute complex velocity profiles — ramp up, hold, ramp down, reverse — with precision that open-loop control cannot approach.

Five Questions That Drive the Decision to Select A Servo or Stepper Motor For a Hollow Rotary Table

Is the motion index-and-dwell, or does it involve continuous rotation or complex velocity profiles? Index-and-dwell is stepper-compatible. Continuous or complex motion profiles need a servo. How consistent is the payload between cycles? Consistent and well-characterized loads work open-loop. Variable or unknown loads need closed-loop control. What angular accuracy does the application require at the table output? Coarser than ±0.05° — stepper with worm gear is generally adequate. Tighter than that — servo with encoder feedback is required. What is the required cycle rate? Relaxed, moderate cycle rates suit steppers. Aggressive throughput targets with fast index moves need servo peak torque capability. What is the consequence of a position error? If a missed step or angular deviation scraps a part, damages equipment, or creates a safety issue — closed-loop position feedback is mandatory.

The Practical Conclusion to Select  A Servo or Stepper Motor For a Hollow Rotary Table