SINUMERIK 810T Spindle Jaw Interlock Troubleshooting After

Problem Definition

A field-reported failure mode on lathes equipped with SINUMERIK 810T / 810M controls (for example, the Amco 342 lathe) presents as follows: a complete parameter and PLC program loss caused by an exhausted backup battery, after which the operator reloads the archive through a serial cable into the controller. The axes and hydraulics return to service, but the spindle chuck jaws no longer open or close when the operator presses the panel pushbutton. The PLC status display confirms the input toggles 0→1 when the button is pressed, yet the corresponding PLC output remains at 0. No fault or alarm is raised.

This article walks through the diagnosis path for that exact symptom: input present, output absent, no alarm. It assumes a Siemens 810T control on a hydraulic chuck, with PLC logic implemented in STEP 5 (the 810T integrates an S5-130W or S5-150A PLC submodule, depending on hardware revision). All references are oriented toward the field engineer restoring service on the shop floor with only the operator panel, a STEP 5 programming device, and basic electrical instrumentation.

System Architecture Recap

The SINUMERIK 810T is a turning-specific CNC introduced by Siemens in the mid-198s and widely deployed through the late 1990s. Its I/O and logic subsystem is implemented as a SIMATIC S5 PLC embedded in the NC rack. The PLC exchanges flags with the NC channel via a fixed interface area in the so-called V-byte / flag-byte range and dedicated ready-to-run and stop signals.

When the parameter and PLC battery is depleted, the controller loses the contents of all NV-RAM that is normally held by the buffer battery (typically a 3.6 V lithium or alkaline pack). On the next power-up, the user is prompted to load the machine data (MD), setting data (SD), tool data, and PLC program from a backup archive. If the backup is incomplete or the MD area is left in default values, the PLC program may load successfully, but its interlock conditions will never be satisfied because the NC never asserts the upstream flags it normally expects.

Root Cause Analysis: Why the Output Never Goes High

On a 810T, the chuck open/close output is almost always gated by a chain of safety conditions. Even if the ladder rung containing the jaw-output coil looks trivially simple in isolation, in the running machine the coil is fed by an AND-gate of:

1. Operator button input (debounced and latched by the OEM macro).
2. Spindle STOP condition (spindle speed = 0).
3. Spindle drive ready / no drive fault.
4. Hydraulic pressure OK (pressure switch feedback).
5. Door interlock or guard closed.
6. No active NC alarm or reset state.
7. Optional: chuck-closed limit switch (for jaw-open path) or chuck-open limit switch (for jaw-close path).

After a full parameter loss, the most common reason items 2-6 fail to assert is that the NC never gets into the operating state required to set the interface flags the PLC expects. Items 1, 4, and 5 are pure hardware and read correctly because the input toggles in the PLC status display and the limit switch chain is mechanically sound. The fault is therefore upstream of the PLC output coil, in the NC-side conditions that are checked by the ladder.

Specific Signal: "Spindle STOP"

On 810T/M, the spindle stop state is communicated from the NC to the PLC through a fixed interface flag. The conventional assignment on most OEMs using the standard Siemens interface is:

• Flag byte for spindle signals: typically FY 40 through FY 44 (vendor-dependent; verify against the project I/O assignment list printed with the backup).
• Spindle STOP bit: often F 41.7 or F 43.5 depending on the cycle macro used by the OEM. Some Amco 342 implementations route it through FY 36.
• Set condition: NC sets the bit high only when the spindle actual speed has dropped below the spindle-zero-speed threshold MD and the spindle drive is in enabled state.

If the spindle drive enable is not asserted (because a drive parameter reset to default), the spindle will not enter its zero-speed state cleanly, and the interface bit will stay low indefinitely, holding the jaw output off without raising an alarm.

Diagnostic Procedure

Step 1: Confirm the input and isolate the failure point

1. Place the control in JOG mode and select the chuck-jaw manual function if the panel has one. If not, use the OEM-assigned M-code or the auxiliary-function screen.
2. Press and hold the jaw open/close button.
3. Open PLC status on the 810T panel: Menu → Diagnostics → PLC Status (path may vary slightly with software version).
4. Locate the input bit (for example, I 32.6). Confirm it toggles 0→1 when the button is pressed. If it does not, the failure is in the button, wiring, or input card; stop here and chase the 24 V signal back to the I/O rack.
5. If the input toggles correctly, navigate to the output bit (for example, Q 32.0). It must remain 0 in spite of the input.

Step 2: Force the output and prove hardware

This step exists to prove the PLC output card, wiring, solenoid, and hydraulic valve are functional. It must be done with the spindle mechanically locked and the hydraulic pressure verified.

1. Select PLC → Force on the 810T panel (or use STEP 5 online force from a PG).
2. Force the output bit to 1 permanently. Many 810T installations require a password; the OEM default is often 1111 or EVENING. Some Siemens-standard passwords for older controllers are SUNRISE or CUSTOMER. Confirm with the machine builder documentation.
3. Listen and observe the hydraulic valve solenoid. You should hear the coil energize and the directional valve shift.
4. Verify the jaw cylinder moves by watching the chuck body.
5. If the output forces correctly and the jaws move, the hardware chain is proven good. The fault is upstream in the ladder logic, specifically in the interlock gating the output coil.
6. Remove the force immediately and re-establish normal control.

Step 3: Online STEP 5 trace of the interlock chain

Connect a Siemens PG (programming device) with STEP 5 to the 810T through the RS-232 service port on the operator panel. Establish an online connection. With the chuck-jaw button held:

1. Open the FB/OB containing the jaw-output coil (typically OB 1 with the jaw function in a vendor-named FB such as FB 100, FB 200, or an PB block).
2. Use Status (online monitor) to view the rung driving the output coil.
3. Walk the rung left-to-right (or by AND terms) and identify the first condition that is false.
4. Record the address of the failing flag/merker. Cross-reference it against the NC/PLC interface listing.

The most frequent offenders, in descending order:

Step 4: Verify machine data is not silently at default

The 810T stores machine data (MD) that defines behavior the PLC and NC rely on. After a battery loss and a partial reload, the user might inadvertently leave MD at factory default. Check, at minimum:

• MD 200* / 300* series: general machine configuration.
• MD 400* / 500*: spindle configuration, including zero-speed threshold.
• MD 9000+: user / OEM area, often used by the lathe builder for chuck logic enable.

If the OEM used MD to enable or disable chuck functions (for example, MD bit that allows chuck open only when M00 is active or only in JOG), confirm the MD area matches the printed backup parameter list from the machine documentation.

Special Case: Amco 342 Lathe with Siemens 810T

The Amco 342 is a two-axis CNC lathe widely sold in the late 1980s and 1990s. Many of these machines shipped with Siemens 810T controls and a separate hydraulic pack for the chuck and tailstock. The Amco PLC program is typically structured around vendor FBs and uses:

• Chuck-open output: Q 32.0 (verify against the project's symbol table).
• Chuck-close output: Q 32.1.
• Jaw manual button input: I 17.0 or I 32.6 depending on hardware revision.
• Chuck-closed limit switch: I 33.0.
• Chuck-open limit switch: I 33.1.
• Spindle-zero-speed flag from NC: typically F 41.7.

On the Amco 342, the chuck-open rung is commonly:

A I 32.6          // jaw open button
  A F 41.7          // spindle stop
  A I 33.0          // chuck closed limit
  AN I 33.1         // NOT chuck open limit
  A I 17.4          // hydraulic pressure OK
  AN F 50.0         // no NC alarm
  = Q 32.0          // jaw open solenoid

If any one of these addresses is false, the rung fails silently. After a parameter loss, the most frequent single failure is F 41.7 being stuck at 0 because the spindle drive is not configured correctly in MD and never reaches zero speed with the drive enabled. The second most frequent is I 17.4 (hydraulic pressure switch) if the new hydraulic power-up sequence has the pump in a different state than the original.

Solution: Restoring Normal Chuck Operation

1. Reload full MD/SD/TOOL/PLC archive. Do not assume a partial backup is acceptable. The 810T archive format is typically an .ARC file transferred via V.24 / RS-232 from a PG or via the SinuCom parameter loader. Cross-check the file size against the original documented size.
2. Power cycle the control with the backup loaded, then enter the commissioning area and verify MD values against the printed parameter list.
3. Confirm spindle drive is operational. With NCK ready and drive enable asserted, the spindle should report "ready" in the diagnostics screen. If a drive fault is pending, clear it at the drive first; on SIMODRIVE 6SC61 this may require acknowledging via the drive keyboard or setting the relevant MD.
4. Confirm spindle stops to 0 rpm before any M-codes or auxiliary functions. Use the actual-spindle-speed display in the 810T to verify the spindle reaches zero. Some drives report zero speed only after the ramp completes.
5. Press the jaw open/close button in JOG. Watch the chuck operate. If still not operating, run the online STEP 5 status trace again.
6. If a single interlock remains stuck false, investigate that specific signal. For NC-side flags, fix the upstream NC condition. For PLC-side flags or inputs, fix the sensor or wiring.
7. Document the corrected MD and the ladder cross-reference for future reference. Print the FB/OB pages containing the chuck interlock and store them with the machine documentation.

Verification Checklist

Troubleshooting Matrix

Common Pitfalls After Parameter Loss

• Reloading only the PLC program and not the MD. The PLC may then request machine states that the NC never reaches because MD is at default.
• Leaving the spindle MD at default zero-speed threshold. The NC may interpret any low speed as not-zero-speed and never assert the spindle-stop flag.
• Forgetting to load the tool data and work offsets. Although unrelated to chuck operation, the machine will alarm elsewhere and the operator may interpret cascading errors as chuck-related.
• Force mode left on after testing. The next cycle will execute the rung with the forced bit and may bypass interlock conditions.
• Spindle drive 6SC61 / SIMODRIVE parameters not reloaded. On Amco and similar lathes, the spindle drive has its own EEPROM that can also lose data. The chuck interlock cannot assert if the drive reports a fault or "not ready".

Field Commissioning Tips

• Always print the I/O assignment list from the original commissioning archive and laminate it. It is the fastest reference when an interlock fails years later.
• After any battery replacement, perform a controlled power-down of at least 30 seconds before disconnecting the old battery, to allow the controller to write any volatile buffers.
• Document the password used for force mode; the OEM default is rarely the one in service after years of ownership changes.
• When stepping through the ladder, take a screenshot of the entire rung with both status on and force list shown. This becomes part of the machine file.
• For a 810T control, always keep a known-good archive on a USB drive in the electrical cabinet. Many PC tools (such as SinuCom or a generic terminal with XMODEM) can reload the archive in 5-10 minutes.

Standards and Documentation References

Field engineers restoring 810T systems should consult the Siemens SINUMERIK 810T commissioning manual and the SIMATIC S5-130W / S5-150A programming guide. Both documents are available through Siemens Industry Online Support. Specific items to reference for chuck-interlock work include the NC/PLC interface signal table for the spindle channel and the safety-related machine data listing. Always cross-check the I/O assignment list printed with the original machine documentation before changing ladder logic.