Free Engineering Tool
Soft Foot Calculator
Check for machine frame distortion by entering dial indicator readings at each foot. Identify the worst soft foot, determine shim corrections, and verify acceptable limits.
Results
| Foot | Reading (mm) | Reading (μm) | Status | Shim Needed |
|---|
What is Soft Foot?
Soft foot occurs when one or more machine feet do not make full, flat contact with the baseplate or foundation. When the hold-down bolt at that foot is tightened, the machine frame is distorted, causing internal stresses that misalign bearings and seals.
Acceptance Criteria
| Reading | Status | Action |
|---|---|---|
| < 0.05 mm (50 μm) | PASS | Acceptable — no correction needed |
| 0.05 – 0.10 mm (50–100 μm) | WARNING | Marginal — correction recommended |
| > 0.10 mm (100 μm) | FAIL | Excessive — must correct before alignment |
Types of Soft Foot
- Parallel (Gap) Soft Foot — uniform gap under the foot. Caused by missing or incorrect shims. Corrected by adding flat shims equal to the gap.
- Angular Soft Foot — wedge-shaped gap where the foot rocks on one edge. Caused by non-parallel machining. Corrected with tapered or stepped shims.
- Springing (Reactive/Induced) Soft Foot — caused by external forces such as pipe strain, conduit stress, or dowel pin binding. The foot appears flat but the frame deflects. Must address the external force source.
Measurement Procedure
- Tighten all machine foot bolts to normal torque.
- Mount a dial indicator (or use a laser alignment system) on the machine frame near Foot 1.
- Zero the indicator, then loosen the bolt at Foot 1.
- Record the maximum dial indicator movement — this is the soft foot at Foot 1.
- Re-tighten the bolt at Foot 1.
- Repeat for each remaining foot.
Practical Example
Readings: Foot 1 = 0.02 mm, Foot 2 = 0.08 mm, Foot 3 = 0.03 mm, Foot 4 = 0.15 mm
Foot 4 = 0.15 mm → FAIL (exceeds 0.10 mm limit)
Foot 2 = 0.08 mm → WARNING (between 0.05 and 0.10 mm)
Feet 1 and 3 → PASS (below 0.05 mm)
Correction: Add 0.15 mm shim under Foot 4, then re-check all feet.
💡 Tip: Always correct soft foot before performing shaft alignment. Soft foot will cause alignment readings to be inconsistent and non-repeatable.
⚠️ Note: If loosening a bolt gives a negative reading (foot lifts), this indicates springing/reactive soft foot caused by external forces. Do not add shims — instead, identify and relieve the external force (pipe strain, conduit, etc.).
Professional alignment and vibration analysis instruments with built-in soft foot detection. Achieve precision alignment on-site. Used in 50+ countries.
Nikolai Shelkovenko
Nikolai Shelkovenko is a vibration analysis engineer and the founder and CEO of Vibromera. For more than 15 years he has balanced rotating equipment in the field rather than on a test bench: mulchers, industrial fans, crushers, centrifuges, shafts and spindles. That work is what the Balanset instruments grew out of — they were designed as a tool a specialist can carry to the machine and use alone, on site, not as laboratory equipment. Vibromera was founded in 2017 and has been based in Porto, Portugal, since 2023. Development, assembly and support of the Balanset line all happen here. The flagship instrument is the Balanset-1A, a portable analyser for single- and two-plane balancing and for vibration diagnostics. Nikolai is personally involved in customer support, in working through difficult balancing cases and in the development of the software. He works with customers worldwide, in any language.
