SINUMERIK MD 12010: Cap Feed Rate Override at 100 Percent

1. Problem Description

On the machine control panel (MCP) of a SINUMERIK-controlled milling or turning centre, the feed-rate override rotary selector is delivered as a continuous encoder (analog track or Gray-coded switches) that the PLC samples, scales and forwards to the NCK as a percentage. Many MCP variants ship with a top detent that lifts the effective override to a value greater than 100% (commonly the headroom used by CAM-posted programs or by end-users who want to push a feed-limited cycle past its written F-value).

End-user requirement in this case is unambiguous: the override pot must top out at exactly 100%. Any further rotation must be inert - turning the pot higher must change nothing - while 0% to 100% must remain fully functional and linear. This is a quality / process control constraint, not a performance one. Cycle macros and CAM-posted programs are typically verified at 100%; silently running them at 120% invalidates tool-life assumptions, violates the chip-load envelope the cutter was specified for, and produces surface-finish variation that the part inspection does not expect. The constraint also simplifies operator training because the HMI channel-status "Override" readout cannot disagree with the programmed feed.

2. SINUMERIK Override Signal Architecture

The SINUMERIK exposes three categorical override signals from the PLC to the NCK. The names confirmed by the SINUMERIK Basics manual section 18.4 ("Vorschubbeeinflussung") are:

Each of the three override channels is fed from a separate rotary or electronic switch on the MCP. The PLC samples the encoder, scales each detent to a percentage, and writes that percentage into the corresponding NC interface word. The NC then multiplies its programmed feed by (override / 100.0) (or equivalently, by the factor returned from MD 12010 after indexing into that MD on the live override percentage).

3. Root Cause of the Unbounded Pot

The override potentiometer hardware has no enforced ceiling of its own. The displayed override is the product of three things:

1. The maximum percentage the PLC's MCP evaluation block writes into the NC interface (typically determined by the highest detent of the rotary switch and the firmware table inside the MCP).
2. The MD 12010 factor table that the NC applies per percentage level.
3. Any curve / weighting applied by additional MDs in the 12xxx family (mode-dependent overrides).

If the PLC always writes the scaled value of the pot back into the NC, and MD 12010's upper indices return a factor of 1.0 along an unmodified curve, the override simply tracks the pot 1:1. Setting every index whose effective factor would exceed 1.0 to 1.0 collapses the upper range into a flat 100% response without disabling the pot itself. This is exactly what the SINUMERIK maintenance reference describes for this constraint.

4. Solution: Configure Machine Data MD 12010

The general (Allgemeine) machine data 12010 — designated Faktor Achsvorschub Override ("axis-feed-override factor") — is implemented as an array indexed by the override step. Each entry holds a factor that is multiplied with the requested override percentage at the corresponding detent position. The standard SINUMERIK maintenance practice for the constraint "cap at 100%" is:

Overwrite every index whose nominal factor would exceed 1.0 with the value 1.0.

The NC then evaluates up to the last index whose factor is still within the 0…1.0 range; any further rotation of the pot returns the same effective override (the highest valid step).

Effect on the three override channels:

• OVR (path feed): clamped at the channel level after MD 12010 evaluation.
• OVRA (axis feed): clamped at the axis / channel level after MD evaluation.
• OVRRAP (rapid traverse): in most MCP wirings the rapid pot is the same physical switch; the factor MD family must also be confirmed for rapid in your build, because OVRRAP can be scaled by an adjacent array MD.

5. Prerequisites

• Active NCK startup. MD 12010 requires the Manufacturer access password to write on most SINUMERIK builds. Service level is sufficient for read-only verification.
• A current backup of the machine data via Commissioning → Machine Data → Save, including the area "Allgemeine MD" (general MDs). Mirror the backup to a CF card / NCU local storage; record the file name explicitly.
• A reliable part program with known programmed feeds, plus the ability to run it in JOG/Automatic with reduced spindle speed for the verification step.
• Access to SINUMERIK HMI Operate on the machine (or remote via Operate for PC) and, optionally, TIA Portal / SIMATIC Manager for PLC cross-checks.
• Awareness of which MCP variant is in use (because the index-to-percentage mapping is hardware-defined by the MCP firmware table).

6. Step-by-Step Configuration

Step 1 — Backup machine data

On the SINUMERIK HMI Operate, navigate to Commissioning → Machine Data → Save. Save the entire NC area to the CF card / NCU local storage. Capture the file name in your change log; never silently overwrite a recent archive.

Step 2 — Log in with the appropriate access level

Open Commissioning → Password and enter the manufacturer access password. Without the correct level, MD 12010 is visible but writes are rejected. The exact password scope is documented in the access-level table of the active commissioning manual (Siemens Industry Online Support).

Step 3 — Open the General MD editor

Navigate to Commissioning → Machine Data → General MD. Use the filter / search field to look up 12010. The MD will be displayed with all its indices in a side-by-side edit grid.

Step 4 — Identify the > 100% indices

Read the current entries. Default delivery typically pre-loads entries for the full range the MCP reports. The threshold index where the factor starts to exceed 1.0 defines the highest override the NC will honor. For an MCP reporting 0–200% the indices corresponding to anything above 100% are the targets for clamping.

Step 5 — Set all entries whose values exceed 1.0 to 1.0

Step 6 — Confirm and write

Confirm each cell change via the soft key OK / Set. The change is staged. To activate, press the soft key Set MD active (CFG) or perform an NCK reset, depending on build-specific rule. Some SINUMERIK versions require a complete NC restart (power cycle) before MD 12010 re-evaluation is fully visible at the channel status display.

Step 7 — Archive the modified MD set

Use Save again to write the new values to the persistent archive. Match the file name to a controlled backup slot in your change ticket. Without explicit save, the values can revert after the next NCK restart or service / firmware refresh.

7. Verification

7.1 On-machine quick checks

1. Switch the operator panel to Override and confirm that the HMI reflects the active channel.
2. Rotate the override pot past the 100% mark. The displayed value on the channel-status page must read exactly 100% from the first detent that previously read >100%; further rotation must not advance the readout.
3. Rotate the pot down to 0% and back up. The 0–100% range must remain fully linear with the original resolution. Detents should still feel mechanically distinct.
4. Run a known-feed part program (e.g. G94 F500) in feed-hold, with reduced programmed value first for safety. With the override pot at 100% the displayed feed rate must match the programmed feed rate.
5. Run the same program with the override pot at the maximum detent. The NC-side feed rate must still display 100%, not the higher value the MCP reporting originally produced.

7.2 HMI Operate verification

On the channel status display, Channel → Override, rotate the pot past 100%. The readout shows the NC-side factor as a fraction (1.00 = 100%). This value must clip to 1.00. The mechanical pot position indicator on the MCP itself can still point higher — that is expected and intended.

7.3 PLC online verification (optional)

Open the PLC project in TIA Portal or SIMATIC Manager. The interface data word corresponding to the channel — for example the channel-DB feed-rate override byte for the OVR channel — must continue to receive the un-clamped raw pot value. Confirm that no PLC-side clamp has been added that would mask the MD 12010 effect from logs and audit trails.

8. PLC Interface Considerations

The PLC evaluates the rotary switch and writes the result to the NCK interface. Per the SINUMERIK Basics manual, the canonical signals are:

• OVR: feed-rate override for the path feed (scale factor 1.0 = 100%).
• OVRA: feed-rate override for positioning axes (incremental positioning and "rapid in axis" movements).
• OVRRAP: rapid-traverse override for G0.

The recommended split of authority is: PLC forwards the raw scaled value; MD 12010 acts as the final clamp. This split keeps all clamps in a single, version-controlled configuration object (the MD archive) and survives any part-program or synchronized-action override command issued inside the NC.

9. Related Machine Data in the Override Family

The other 12xxx machine data in the override family cover mode-dependent chains (path feed in G93/G94/G95, rapid traverse, dry-run, single-block mode deductions, handwheel override in JOG, etc.). Treat them as siblings of MD 12010. Because the exact role of each MD in the 12xxx range is build-specific, consult the active SINUMERIK commissioning manual (SIOS) before extending the cap to those flows. The conservative approach is to apply the "1.0 ceiling" rule uniformly across every override factor MD in the family after confirming that the build's MD list makes that MD the relevant one.

10. Troubleshooting Matrix

11. Safety and Operational Notes

Cap the override at 100% only after the part-program library has been written under the assumption that 100% is the practical ceiling. If existing programs were posted against 120% as an authorized machining regime, capping the override will require a controlled re-issue of those programs (or at minimum an explicit user-acknowledged warning displayed at first run). Document the change in the machine's Wartungs- und Bedienungsanleitung so operators encountering a "dead" upper detent understand it is intentional, not a fault.

Always re-archive (save) the modified MDs and include them in the next backup cycle. Many sites have lost an override clamp during a firmware upgrade when the upgrade tool re-applied the vendor default archive. Treat the override-clamped archive as the canonical restore point for that machine and protect it from being overwritten by automation that calls the default configuration.

For reference design of the override interface and the cross-link between PLC and NCK, consult the active SINUMERIK "Basic Functions" (Grundfunktionen) manual via Siemens Industry Online Support; the manual is searchable under the term Vorschubbeeinflussung. The corresponding SINUMERIK product overview is available on the SINUMERIK product page.

12. Frequently Asked Questions