I. Preparing for Measurement: Environment and Cleanliness
Pin gauges are typically accurate to the micrometre (μm) level; even the slightest disturbance can render measurements meaningless.
1. The 20°C Thermal Equilibrium Rule:
○ Key Consideration: Pin gauges have an extremely low heat capacity; contact with body temperature (36°C) for just a few seconds can cause significant linear expansion.
○ Procedure: The pin gauge and workpiece must be allowed to reach thermal equilibrium at $20^\circ\text{C}$ for at least one hour.
○ Expert Advice: Always wear dust-free, heat-insulating gloves or use dedicated pin handles during operation to prevent the transfer of body heat.
2. Chemical Cleaning:
○ Use industrial-grade **anhydrous ethanol** in conjunction with a lint-free microfibre cloth.
○ Note: Do not use ordinary alcohol containing water, as this may form a microscopic water film on the pin gauge’s surface, leading to subsequent corrosion.
3. Visual Inspection:
○ Examine the measuring end face under a magnifying glass. Check for any signs of **galling** (particularly metal residue adhering after measuring aluminium parts).
II. ‘Fine-Tuning Techniques’ During Measurement: Technique Determines Accuracy
The gauge is a ‘probe’, not a ‘punch’.
1. Axial Alignment:
○ The gauge must be perfectly aligned with the centreline of the hole being measured. An angled insertion may result in a “false non-pass” or scratch the bore wall.
○ Technique: When measuring vertical bores, allow the gauge to slide in using its own weight; do not force it in by hand.
2. “Pass/Fail” Criteria:
○ GO (Pass Gauge): Must slide smoothly through the entire bore.
○ NO-GO (Fail Gauge): The insertion depth must not exceed $2 \times \text{Diameter}$ (or as determined by specific industry standards).
○ Warning: If resistance is encountered, stop immediately. Forcing the gauge in will cause a ‘cold welding’ effect, resulting in the gauge and workpiece becoming seized together, damaging both.
III. Material-Specific Maintenance: Leveraging the Core Advantages of Mihe Products
Different maintenance strategies should be adopted for Mihe’s three main product lines: white steel, tungsten steel and ceramic:
| Material types | Maintenance challenges | Professional advice from Mi and our engineers |
| Stainless steel | Prone to oxidation and rusting | Wipe off any residual cutting fluid immediately after use and apply rust-preventative oil. The relative humidity of the storage environment should be $< 50\%$. |
| Tungsten carbide | Highly brittle, prone to chipping | Extremely high hardness (five times more wear-resistant than steel), but must be protected from impact. Do not store multiple tungsten steel gauges together. |
| Ceramic | Poor impact resistance | Mi and Star Products: Completely rust-free, acid and alkali resistant, and non-magnetic. Simply keep clean; the ideal choice for medical and semiconductor applications. |
IV. Guidelines for Daily Storage and Avoiding Common Pitfalls
1. Vertical Storage Method:
○ Gauges should be stored in a **dedicated pin case** with holes, keeping them separated vertically or horizontally.
○ Do not: Under no circumstances should gauges be left loose in a toolbox or on a metal work surface, as if they were pens.
2. “No Wringing”:
○ Do not attempt to measure gaps by wringing two gauges together side by side. The contact stress on the cylindrical surfaces of the gauges is extremely high, making permanent scratches highly likely.
3. Demagnetisation:
○ Steel gauges may become magnetised during prolonged use, attracting metal particles and causing dimensional deviations. Regular demagnetisation is recommended.
V. Digital Management and Calibration (Metrology Management)
1. Wear Monitoring (Wear Allowance):
○ According to the EURAMET cg-6 standard, the leading edge of a pin gauge wears first. During calibration, it is essential not only to measure the centre but also to focus on checking the roundness and straightness of the ends.
2. Traceability Certification:
○ Metrology and Commitment: Each set of gauge pins must be cross-checked against the metrology records and the in-house test report from the German Jena length measuring instrument prior to dispatch.
○ It is recommended that companies establish a ‘colour-coding’ system: green indicates the gauge is within its validity period, whilst red indicates it requires inspection.
