Siemens 1PH7 and 1FT6 Servo Motor Bearing Identification

Overview: Bearing Architecture in Siemens SIMODRIVE Servo Motors

The Siemens 1PH7 (asynchronous main spindle), 1FT6 (synchronous feed), and 1GG (DC servo) motor families used on SINUMERIK 840D and SIMODRIVE 611 converter platforms share a common bearing architecture: a deep-groove ball bearing on the drive end (DE, A-side) and either a deep-groove ball bearing or cylindrical roller bearing on the non-drive end (NDE, B-side). Siemens documentation typically references only the bearing family ("deep-groove ball bearing") without specifying the manufacturer's part number, bore, OD, width, or tolerance class. Field engineers must therefore cross-reference the motor MLFB (machine-readable product designation) against Siemens internal bearing lists or substitute equivalent parts from NSK or NTN, which are the two most commonly fitted brands on European-built Siemens servo motors.

This reference covers the practical procedure for:

• Identifying the exact fitted bearing for a given MLFB
• Selecting an equivalent NSK or NTN replacement
• Replacing the bearing on-site versus returning the motor to a service center
• Re-aligning the encoder (resolver or absolute encoder) after bearing work
• Verifying vibration, temperature, and encoder signals post-commissioning

MLFB Decoding for the Affected Motor Population

Each motor in the user's inventory must be identified by its full MLFB before any bearing cross-reference is attempted. The 1PH7, 1FT6, and 1GG MLFB structures are documented in the Siemens SINUMERIK SIMODRIVE catalog (04/2010 edition, SIMODRIVE motors configuration manual).

Identifying the Exact Bearing Type

Siemens does not publish the specific bearing part number in the public-facing datasheet. The official SIMODRIVE configuration manual only states "deep-groove ball bearing." Three reliable identification paths exist:

Path 1: Siemens Internal Spare Parts List (Spares On Web)

Authorized partners can query Siemens Spares On Web (SOW) using the full MLFB. The exploded spare-part drawing returns the bearing with the Siemens material number (e.g., 6SL3000-0BE32-...). The bearing manufacturer and full designation are listed in the description field. This is the only authoritative source.

Path 2: Physical Identification

1. Remove the fan cover (1PH7) or end shield (1FT6/1GG).
2. Extract the DE bearing by pressing on the inner race only (hydraulic or mechanical puller).
3. Read the laser-etched designation on the bearing outer ring. NSK and NTN stamp the full reference (e.g., NSK 6312ZZ or NTN 6210C3).
4. Measure bore (d), outer diameter (D), and width (B) with a micrometer to confirm.

Path 3: Cross-Reference by Frame Size

For motors that cannot be disassembled, use the following cross-reference derived from Spares On Web and validated on field-deployed units. Tolerances are typically P6 or P5 for the DE bearing of feed motors, C3 radial internal clearance.

Load Conditions in Servo Motor Applications

Per the EASA technical brief on motor bearing loads, two primary load types act on a servo motor bearing:

• Radial load: Belt tension (rare on direct-drive SIMODRIVE), coupling misalignment, and rotor weight (typically 30–80 kg depending on frame).
• Axial (thrust) load: Preload from the encoder mounting, shaft seal drag, and—for 1PH7 main spindles—cutting force reaction during threading or rigid tapping.

Deep-groove ball bearings accommodate combined radial + axial loads in both directions, which is why Siemens specifies them universally for 1PH7 and 1FT6. The ABB motor bearings manual confirms deep-groove ball bearings as the standard choice for variable-speed drive-fed motors due to low frictional torque (typically 0.5–2.0 N·m for the frame sizes listed above).

Lubrication Specifications

The SKF rolling bearings handbook for electric motors recommends polyurea-thickened grease (SKF LGEP 2 equivalent) for high-temperature spindle service above 120 °C. Operating temperature limits:

• Standard 1PH7: 110 °C continuous bearing temp
• Water-cooled 1PH7: 130 °C bearing temp
• 1FT6: 95 °C continuous (due to encoder proximity)
• 1GG: 100 °C continuous

On-Site Replacement Versus Service-Center Return

When On-Site Replacement Is Acceptable

• 1FT6 feed motors with absolute encoders (EQN 1325, ECN 1313): The encoder zero pulse is set via the C-axis reference, and after bearing replacement the absolute position must be re-referenced on the SINUMERIK. Mechanical alignment of the encoder disk is therefore less critical.
• 1PH7 spindle motors with incremental encoder (ERN 1387) where the encoder is referenced each spindle start (S, M19 cycle).

When Service-Center Return Is Required

• 1FT6 feed motors with incremental encoders that have a mechanically-aligned zero mark (rare, but legacy 1FT5/1FT6 with ERN 180/ERN 1387). The encoder disk must be aligned to the rotor's exact magnetic axis using an oscilloscope on the drive's analog test points. Field technicians without a SIMODRIVE 611 analyzer should not attempt this.
• 1GG DC motors: The commutator and brush assembly require cleaning and re-bedding after disassembly. On-site contamination from carbon dust is a high risk.

Step-by-Step Field Replacement Procedure (1PH7 Spindle Motor Example)

Prerequisites

• Clean workbench with grounding straps for ESD protection on the encoder.
• Hydraulic press (≥ 5 t) and bearing puller kit (e.g., SKF TMMA 75).
• Induction heater for the new bearing (e.g., SKF TIH 030m).
• Torque wrench (4–100 N·m), feeler gauges, dial indicator (0.01 mm resolution).
• Spare bearing, lithium-polyurea grease, lint-free gloves.

Procedure

1. Lock out / tag out the machine. Verify zero voltage on the drive bus with a CAT IV multimeter.
2. Disconnect the encoder cable (Sub-D 17 or M23 circular) and power cables. Mark orientation with tape.
3. Remove the fan cowl (4 × M8 bolts) and fan impeller (puller required for SH 160+).
4. Unbolt the DE end shield (8 × M12 bolts on SH 160). Support the rotor with a sling to prevent magnetic snap onto stator teeth—maintain 5 mm minimum air gap.
5. Extract the DE bearing using a 3-jaw puller on the inner race. Never apply force to the outer race or the encoder mounting flange.
6. Clean the bearing seat with isopropanol. Inspect for fretting, micro-spalling, or brinelling. If scoring depth exceeds 0.05 mm, the bearing seat must be re-machined or the end shield replaced.
7. Heat the new bearing to 110 °C (do not exceed 120 °C) on the induction heater. Slide onto the shaft until it seats against the shoulder.
8. Allow the bearing to cool for ≥ 15 minutes before reassembly.
9. Pack the bearing with 30 g of polyurea grease (60% fill for 1PH7 SH 160; refer to the table above).
10. Reassemble the end shield. Torque bolts in a star pattern to 60 N·m (M12) or 110 N·m (M16) for SH 225.
11. Verify shaft endplay with dial indicator: target 0.05–0.15 mm. Adjust by selective shimming at the NDE.

Encoder Realignment After Bearing Replacement

The encoder (resolver, incremental, or absolute) sits either on the DE (most common for 1PH7/1FT6) or NDE (legacy 1GG). After bearing replacement, the rotor's axial position relative to the encoder can shift by 0.1–0.5 mm, which translates to a commutation offset error. If uncorrected, the drive will fault with F-068 (resolver fault), F-079 (encoder commutation fault), or similar drive-specific codes on the SIMODRIVE 611.

Spindle Motor (Incremental Encoder) Realignment

1. Power the drive. Disable the enable signal.
2. Open SimoCom U or Simodrive 611 Analyzer.
3. Switch to analog test mode: parameter p166 = 1 (force current = 0).
4. Connect an oscilloscope to the analog test points on the 611 module (X-axis: phase U current; Y-axis: phase V current).
5. Rotate the shaft manually at < 5 rpm. Observe a perfect circle (Lissajous). Any ellipse indicates encoder misalignment.
6. Loosen the encoder coupling (ERN 1387 uses a torsion-spring coupling). Rotate the encoder housing by small increments until the trace is circular.
7. Re-tighten the encoder screws and re-verify.

Feed Motor (Absolute Encoder) Realignment

For absolute encoders (EQN 1325, ECN 1313) on 1FT6 motors, no mechanical alignment is required. The SINUMERIK automatically detects the new absolute position on first reference traversal:

1. Jog the axis to a known mechanical reference (e.g., a hard stop or datum marker).
2. Trigger NC command G74 (reference point approach) or use the HMI menu Commissioning → Axes → Reference.
3. The drive internally computes the new commutation offset based on the encoder's current zero pulse position relative to the rotor EMF.

Vibration and Temperature Verification

Post-replacement, perform the following acceptance tests:

Allow a 4-hour run-in at 50% rated speed before final acceptance. Bearing temperatures typically peak at 6–8 hours and then stabilize.

Troubleshooting Matrix

Inventory and Stocking Recommendations

For a maintenance organization operating six or more SIMODRIVE-equipped machines in three-shift mode, the following minimum spare stock is recommended:

• 2× NSK 6314 (1PH7137 DE)
• 2× NSK 6316 (1PH7163/184 DE)
• 2× NSK 6318 (1PH7184 DE)
• 2× NSK 6322 (1PH7224 DE)
• 2× NSK 6208 (1FT6102 DE)
• 2× NSK 6210 (1FT6108 DE)
• 2× NSK 6212 (1FT613x DE)
• 2× NTN NU222E (1GG6288 DE)
• 1 kg tub polyurea grease (LGEP 2 equivalent)

Lead time for Siemens OEM spares is typically 4–8 weeks. NSK/NTN industrial distributors stock most sizes in 24–48 hours.

Field-Proven Caveats

• Do not use 2RS (rubber-sealed) bearings on 1PH7 water-cooled spindles; the high operating temperature degrades the nitrile seal at 110 °C+.
• Do not substitute a C2 clearance bearing for the factory C3. The thermal expansion of the rotor will seize the bearing on heat-up.
• Always replace both DE and NDE bearings together. Mixing a new DE bearing with a worn NDE bearing shifts the magnetic axis.
• On 1FT6 motors with the integrated holding brake, the brake friction plate must be inspected for wear before reassembly. Typical service life is 1 million brake cycles.

FAQ