Soft foot is a condition where one or more machine feet do not make complete, flat contact with the baseplate. When the hold-down bolt is tightened, it distorts the machine frame, causing internal stresses and misalignment of bearings and shaft. The reading is typically 0.05 mm or more when loosening a foot bolt.

Why does soft foot matter?

Soft foot distorts the machine frame when bolts are tightened, causing internal bearing misalignment, inconsistent alignment readings, increased vibration, premature bearing failure, and the inability to achieve repeatable shaft alignment.

How do I measure soft foot?

Mount a dial indicator on the machine frame near each foot. With all bolts tight, loosen one bolt at a time and record the dial indicator movement. The reading represents the gap (soft foot) at that location. Re-tighten before moving to the next foot.

What are the types of soft foot?

There are three main types: 1) Parallel (gap) soft foot — uniform gap under the foot, corrected with flat shims. 2) Angular soft foot — wedge-shaped gap, corrected with tapered or stepped shims. 3) Springing (reactive/induced) soft foot — caused by external forces like pipe strain or conduit stress distorting the machine.

How do I correct soft foot?

For parallel soft foot: add flat shims equal to the dial indicator reading under the affected foot. For angular soft foot: use stepped or tapered shims. For springing foot: address the external force (pipe strain, conduit stress, dowel pin binding) rather than adding shims. Always re-check after correction.

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.

4 or 6 Feet Pass / Warn / Fail Shim Recommendation

Number of Feet

Dial Indicator Readings (mm — reading when bolt is loosened at each foot)

Foot 1 (mm)

Foot 2 (mm)

Foot 3 (mm)

Foot 4 (mm)

Quick presets

Results

Worst Foot Identified

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Overall Status

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Recommended Shim

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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.

Shim thickness = Dial indicator reading at the soft foot

Practical Example

Example — 4-Foot Motor

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.).

Soft Foot Calculator — Free Machine Frame Distortion Check

Published by Nikolai Shelkovenko on February 15, 2026 March 5, 2026