A repeatable compression test begins before the first data point. The spring must be seated consistently, the load and travel envelopes must be appropriate, and the measurement reference must be unambiguous.

1. Confirm the test definition

Start from the drawing, customer specification or approved internal plan. Identify the required force-at-length or force-at-deflection points, any rate interval, the maximum permissible load and travel, the number of repetitions and the acceptance limits.

Do not use the test machine to discover safe limits on an unknown spring unless that exploratory work is separately risk-assessed.

2. Choose and inspect the fixtures

Compression platens should be clean, aligned and large enough to support the spring ends. A slender spring may require guidance, but the guide must not add uncontrolled friction. Confirm that the fixture, load cell and frame capacity suit the planned test.

3. Establish preload and datum

A small controlled preload can establish stable contact. Once the eligible preload condition is confirmed, record the absolute machine position as the immutable datum for that test. Test displacement is then calculated as the magnitude of the change from that datum.

STM-X convention: Machine Z remains the absolute coordinate. Test displacement is |Machine Z − preload datum|. Compression supplies the physical direction; the coordinate sign is not repurposed.

4. Run the defined motion

Apply the approved speed, target and dwell settings. Keep every accepted force-position reading paired as one snapshot so the live display, graph, raw trace and report describe the same instant. Where repetitions are required, keep the complete repetition set rather than selecting the best-looking pass.

5. Review the result

  • Verify the test reached the intended target without envelope violations.
  • Inspect the loading and return paths for slip, steps or unexpected curvature.
  • Confirm that the rate interval and evaluation points match the approved recipe.
  • Record interruptions rather than certifying an incomplete trace.
  • Save the batch and report with units, datum provenance and sample identity.

Relevant standard family

ISO 22705-1:2021 specifies measurement and test methods for general characteristics of cold-formed cylindrical helical compression springs made from round wire, excluding dynamic testing. Always consult the licensed standard and the governing customer specification for the exact requirements.

Editorial note

This guide provides general engineering information. Apply the governing drawing, licensed standard, risk assessment and approved procedure for the actual test.