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ISO 28927-4:2010 — Hand-held portable tools — Vibration test for straight grinders
Laboratory method using test wheels of known unbalance for vibration emission measurement | Engineering guide
Introduction to ISO 28927-4
ISO 28927-4:2010 specifies a laboratory method for measuring hand-transmitted vibration emission at the handles of straight grinders. Together with ISO 28927-1 (angle and vertical grinders), it replaces ISO 8662-4:1994. This standard introduces a test wheel of known unbalance to ensure reproducible measurements under no-load conditions.
Straight grinders are defined as grinders where the handle, motor, and spindle are coaxially aligned. The standard covers type 1 straight wheels, type 4 tapered wheels, and cylindrical plugs (types 16, 18, 18R, 19).
Key Technical Requirements
Test Wheel and Unbalance Method
Instead of a real grinding task, this standard uses aluminum test wheels with precisely machined holes to create defined unbalances. The test wheel is geometrically similar to a real grinding wheel but with controlled unbalance characteristics. Type 1 test wheels must be tested in five orientations (0°, 72°, 144°, 216°, 288°) to average out the effects of unbalance orientation.
| Test Wheel | Diameter (mm) | Unbalance (g·mm) | Feed Force (N) |
|---|---|---|---|
| 1:25 | 25 | 3.6 | 15 |
| 1:50 | 50 | 14.5 | 15 |
| 1:80 | 80 | 18 | 15 |
| 1:100 | 100 | 29 | 30 |
| 1:125 | 125 | 45 | 30 |
| 1:150 | 150 | 65 | 30 |
| 1:200 | 200 | 115 | 45 |
For machines equipped with automatic unbalance reduction technology, the declared vibration values must be multiplied by a correction factor of 1.3 before reporting!
Engineering Design Insights
The test wheel design is remarkably elegant: balance screws are mounted in threaded holes to achieve zero initial unbalance, then removed to create precisely controlled unbalance. The unbalance is calculated as the mass of the screw times the radius to the hole center. For example, test wheel 1:25 uses an M5 x 6 set screw (ISO 4026) of 0.43 g at an 8.4 mm radius, giving 3.6 g·mm.
The standard specifies that the test rig base must be bolted to a concrete block of at least 400 kg to prevent resonances. The feed force is applied using a sling and pulley arrangement, counterbalancing the machine weight plus the specified feed force.
The vibration magnitude is corrected for speed variations using the formula: ahvrat = ahvmeas x (nrat/nmeas). This allows comparison of results even when the actual no-load speed differs from the rated speed marked on the machine.
Uncertainty Determination
For straight grinders, the standard deviation of reproducibility sR = 0.2 x ah, based on round-robin tests documented in ISO/TR 27609. This gives K = 0.33 x ahd for single-machine tests.
Frequently Asked Questions
Q: What materials are used for test wheels?
A: Aluminum EN AW 2014 (AlCu4SiMg) or equivalent, with density between 2700 and 2800 kg/m³.
A: Aluminum EN AW 2014 (AlCu4SiMg) or equivalent, with density between 2700 and 2800 kg/m³.
Q: How are bushings selected for mounting?
A: Concentric bushings with zero play are chosen based on the best fit to the spindle. Multiple bore diameters from 3.76 mm to 19.00 mm are specified.
A: Concentric bushings with zero play are chosen based on the best fit to the spindle. Multiple bore diameters from 3.76 mm to 19.00 mm are specified.
Q: Are die grinders covered by this standard?
A: No, die grinders where the inserted tool is mounted in a collet are covered by ISO 28927-12.
A: No, die grinders where the inserted tool is mounted in a collet are covered by ISO 28927-12.
