Published:2026-09-15 00:32:11
Motor bracket shaft alignment and diagnosis
Identify the deviation, then align
Separate offset, angle and axial installation issues when diagnosing heat, vibration or resistance. Check datums, measurement conditions, connections and the final tightened state.
01 / Three distinct checks
Turn a general alignment complaint into measurable questions
Separate shaft offset, angle and coupling axial position when diagnosing an alignment complaint. Drawing requirements such as coaxiality have specified datums and inspection methods; they are not interchangeable with any workshop indicator reading.
| Check | Geometrical meaning | Record | Typical leads |
|---|---|---|---|
| Radial / parallel offset | Nearly parallel axes with different centres at a defined plane. | Horizontal/vertical offset in mm; identify the plane. | Centre-height difference, eccentric locating features, base position or a fit problem. |
| Angular misalignment | Shaft directions differ; offset varies along the axis. | Angle in both planes, or deviation such as mm/100 mm. | Tilted mounting faces, incomplete contact, base distortion or movement during tightening. |
| Axial installation error | Axial positions of shaft ends, hubs or flexible elements fail the coupling requirements. | Spacing, grip length and axial movement allowance. | Incorrect shaft extension, excessive hub insertion, contacting shaft ends or inadequate thermal movement allowance. |
Collinear shafts can still have contacting ends. Axial spacing is a separate check; offset and angle can coexist.
02 / Effects and clues
Coupling reactions can add load, but symptoms alone do not identify the cause
Coupling deformation creates reaction forces or moments at the motor and screw support, depending on coupling type, stiffness and combined deviations. Possible effects include vibration, noise, heat, wear and added bearing load. Lubrication, damage and control settings can produce similar symptoms.
| Observation | Check first | Avoid this conclusion |
|---|---|---|
| Resistance or current increases after coupling connection | Offset and angular alignment, axial spacing, hub grip position and internal interference. | Current alone does not establish excessive preload; compare equivalent conditions. |
| Motor or fixed-end temperature becomes abnormal | Connected/disconnected condition, temperature trends at the same speed and load, lubrication and bearing condition. | Temperature does not identify the direction or magnitude of misalignment. |
| Vibration or noise is stronger at certain speeds | Geometry, fastening, coupling condition and machine resonance. | A frequency component is a diagnostic clue, not proof of bracket misalignment. |
| Tightening increases resistance; releasing a specified joint reduces it | Surface contact, burrs, locating fits, hole positions and base distortion. | Free rotation with loose bolts is not an acceptable delivered condition. |
| Knocking or position changes on reversal | Hub grip, shaft locking, support joints, nut and guide system. | Do not attribute every reversal displacement to alignment or internal bearing clearance. |
Section 3.2 of the Yaskawa LEGEND user manual requires motor-to-machine shaft alignment and warns that installation impacts can damage the encoder. It also specifies motor shaft load limits. These support checking alignment and shaft loads; the numerical values for that motor series are not universal motor-bracket acceptance limits.
03 / Before measuring
Establish the datums and part condition before interpreting runout
- Define the assembly state Record full motor, bracket, bearing-support and coupling models. Identify when the symptom appeared and which mounting datum will remain fixed.
- Isolate and support the mechanism Isolate power and prevent unexpected movement. Secure vertical or gravity-loaded mechanisms before releasing connections or rotating shafts, following the machine service procedure.
- Inspect locating contact Clean the interfaces as instructed. Check pilot, face and base contact; bolts must not force incompatible holes into place.
- Check individual parts Maintain the specified support and axial location. Inspect shaft, journal and hub runout; record measurement points and rotation method.
- Qualify the measuring setup Match instruments to access and limits. Check fixture rigidity, zero return, probe direction and repeatability; replace unsuitable tooling.
A fixed indicator on one rotating shaft measures surface runout, not the offset between two shafts. Qualify a hub outside diameter before using it to represent the shaft axis. Do not divide arbitrary runout by two and report it as coaxiality.
04 / Measure separately
Define a result and an acceptance basis for each direction
Offset: measure the relative shaft positions at a defined plane
Where access permits, use a suitable reverse-dial or laser alignment system. Mount fixtures on shafts or qualified hubs as prescribed. Record measuring-plane distances and horizontal/vertical directions. Rotate to the required positions and retain readings and results. Identify the offset reference plane: with angular misalignment, offset changes along the axis.
Angle: assess shaft direction as well as position
An alignment system or reverse-dial method can calculate angle. Face-based methods require specified surfaces, diameter and rotation procedure, with face runout and axial movement controlled. Four-position gap differences can screen for angle but include face errors. One feeler-gauge reading cannot establish shaft angle.
Axial position: verify installation dimensions and operating movement
Check hub positions, shaft-end spacing, grip lengths and flexible-element length against the coupling drawing. For hidden shaft ends, use approved external datums and the dimension chain. Distinguish installation spacing from operating movement, accounting for screw supports and temperature changes.
| Result | Record | Common misinterpretation |
|---|---|---|
| Offset | Horizontal/vertical values, units, reference plane, measuring-plane distances and method. | Single-shaft surface runout is not the offset between shafts. |
| Angle | Results in both planes; include the full unit and reference length when using mm/100 mm or similar notation. | Face-gap difference across a specified diameter is not radial offset. |
| Axial installation | Target and actual spacing, tolerance, hub grip lengths and operating displacement requirements. | Permissible axial movement does not allow insufficient grip or contacting shaft ends. |
The SKF shaft alignment tool instructions separate horizontal/vertical offset and angle and require remeasurement after tightening. Apply these principles with suitable tooling: short shafts, flange mounting or restricted rotation may need a different setup.
Check fixture sag, axial movement, surface runout, distance inputs and rotation range. Resolve poor repeatability before altering locating surfaces or holes.
05 / Correction sequence
Work from datums to connections and remeasure each confirmed change
| Finding | Correction direction | Verify afterwards |
|---|---|---|
| Pilot or mounting face does not seat | Assess obstructions, burrs, coating and fits against the drawing. Do not force assembly with bolts. | Restored seating, individual part condition and shaft alignment. |
| Base or mounting surface introduces offset or tilt | Use approved adjustment points or an engineering plan for datum repair. | Surface contact, readings before/after tightening and alignment with the screw and guides. |
| Incorrect hub position or axial spacing | Reposition and tighten to the coupling drawing after confirming adequate shaft extension and grip area. | Shaft-end gap, grip lengths, absence of interference and connected alignment. |
| Readings change during final tightening | Check incomplete contact, hole-position constraints and tightening sequence; follow the specified staged procedure. | Geometry at final torque, rather than readings with partially loose bolts. |
| A part or locating interface fails its drawing requirement | Inspect, document and assess repair or replacement. | The replacement interface and complete shaft system, including any original external constraint. |
Do not place local shims under a pilot-located servo flange by copying foot-mounted motor practice. Shims, plates or datum repair need an appropriate engineering plan that preserves location and contact. Avoid moving a guide-aligned screw support simply to meet the motor.
Alignment and bearing preload are different. Do not open an adjusted fixed-end assembly or keep tightening its locknut to remove alignment-related resistance. See the fixed-end support repair guide for service boundaries.
06 / Diagnostic example
Narrow the cause when current rises after connecting the coupling
This diagnostic example is not a customer case or a set of universal limits. Support components correctly and compare only operating conditions permitted by the machine procedure.
- Record what changed Save the conditions and readings before and after connection. Disconnecting changes the load, so current differences alone do not quantify friction loss.
- Check all three items Measure offset at the reference plane and angular alignment, then verify axial spacing and hub positions. Good alignment does not rule out contacting ends.
- Correct one confirmed issue at a time Correct a hub position that fails the drawing, then remeasure. Do not tune the servo to conceal unresolved mechanical resistance.
- Compare the final equivalent states At final tightening and the prescribed operating conditions, check geometry, temperature, vibration and current trends again. If symptoms remain, investigate bearings, lubrication, load and controls.
Improvement does not replace acceptance. A remaining symptom does not prove a replacement part is defective. Record each state and result to distinguish multiple causes.
07 / Acceptance record
Match each limit to its characteristic, method and final assembly state
| Record | Minimum information | Acceptance basis |
|---|---|---|
| Identification and conditions | Full motor, bracket, support and coupling models; drawing revision; speed/load, ambient and cold/warm state. | Ordered configuration, controlled drawings and commissioning procedure. |
| Measurement method | Instrument, resolution, fixtures, surfaces, reference plane, distances and repeatability check. | Confirmed inspection method and instrument suitability. |
| Offset and angle | Horizontal and vertical results before adjustment and after final tightening, with units and limits. | Applicable motor, coupling and machine requirements; assess differently defined limits separately. |
| Axial installation and location | Required spacing, grip lengths, fixed-end location and thermal movement conditions. | Selected coupling and screw-end drawings and the support arrangement. |
| Commissioning | Approved staged conditions; current, temperature, vibration and noise trends; full-travel and post-cooldown checks. | Machine acceptance criteria and comparable baseline records. |
Maximum coupling displacement capability is generally not an installation target. Check combined-deviation limits; do not assume all maxima apply simultaneously. Verify motor shaft load limits for the exact model and load application position.
After cold acceptance at final torque, raise speed in approved stages, pausing if abnormalities appear. Record relevant warm or post-stop conditions by the prescribed procedure. Never approach rotating parts with handheld alignment instruments. See the support-unit installation acceptance checklist for the wider assembly checks.
08 / FAQ
Frequently asked questions
Why align the shafts if a flexible coupling can accommodate misalignment?
Accommodation creates reactions and depends on speed, load and combined deviations. Use the specified installation target, not maximum capability.
Is indicator-measured shaft runout the same as coaxiality?
No. Define the datum, surface and rotation method: fixed-indicator runout and two-shaft offset are different measurements.
Can collinear shafts still have an axial installation problem?
Yes. Incorrect spacing, grip length or thermal allowance can create interference or axial load.
Does an integrated bracket need these checks too?
Yes. Shafts, fits, face contact and base mounting still affect the final assembly.
Is there one acceptable misalignment value for every motor bracket?
No. Match the selected motor, coupling, drawing and machine limits to their measurement definitions and methods.