Three Field Uses for a Portable Roughness Tester
Incoming inspection, between-process sampling and final acceptance use the same instrument in three different ways. The wrong method makes an accurate number meaningless.
1. Incoming inspection: guarding against batch risk
A supplier delivers a batch and you have to decide whether to accept it. This is not one measurement, it is sampling: several parts from the batch, three positions on each, then the distribution against the drawing tolerance.
What matters is scatter. One out-of-tolerance point may be a local defect; a batch running high says the supplier process is off, and that is a conversation about return or price.
2. Between-process sampling: watching for drift
Measure right after turning, milling or grinding to judge whether that pass was right. Here the point is fixed, the frequency is high, and only the trend matters.
Fixed is the whole trick: same machine, same operation, same position, several parts in a row. A number that climbs steadily says the tool is wearing; a sudden jump says fixturing or parameters changed.
3. Final acceptance: guarding against delivery risk
The last gate before shipping. This follows the standard or the customer agreement: sampling ratio, point positions and evaluation length all written down, data retained.
These numbers get reviewed by the customer, so the parameters must match the agreement. An Ra measured at a 0.8 mm cutoff cannot be compared with an acceptance value measured at 2.5 mm.
4. What all three share
A clean surface: oil, swarf and scale lift the stylus.
Fixed parameters: cutoff, evaluation length and filter locked.
Correct direction: measure across the lay, not along it.
Summary
The value of a portable unit is not that it measures. It is that it measures on site, for a stated purpose. Separate the criteria for the three uses and the data starts to support decisions.
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