You check brass part dimensions with a mix of tools. Fixed gauges and hand instruments give fast checks at the machine. A coordinate measuring machine (CMM) or vision system measures complex features and produces a full report.
The right method depends on the feature, the tolerance and how many parts you measure. A good inspection plan says which tool checks each critical dimension.
Common tools and what they check
- Vernier and digital calipers measure lengths and diameters quickly, but are not precise enough for tight tolerances.
- Micrometers measure outer diameters and thicknesses more accurately than calipers.
- Plain plug and ring gauges give a go or no-go check on holes and diameters.
- Thread plug and ring gauges check internal and external threads, including taper threads.
- Height gauges and surface plates check heights, steps and positions.
- Profile projectors and vision systems check small shapes, radii, chamfers and angles.
- Surface roughness testers measure Ra and other finish values.
- CMMs measure positions, angles and geometric tolerances in three dimensions.
When to use gauges
Go and no-go gauges are fast, simple and hard to misread. They suit checks during production, where an operator measures parts every few minutes. They tell you whether a part passes, but not by how much.
Gauges wear, so they need regular calibration against a reference. Ask to see calibration certificates, ideally from a laboratory accredited by NABL, India's accreditation body for test and calibration labs.
If you supply gauges yourself, you remove one source of dispute. Both sides then judge parts against the same reference. Agree who keeps a master set and how often working gauges are checked against it.
When to use a CMM
A CMM suits first article inspection, parts with geometric tolerances such as true position or concentricity, and disputes. It measures actual values, so you can see how close parts are to the limits.
Many small Jamnagar shops do not own a CMM. Some send parts to a nearby measuring service. That is acceptable for samples, but you need a different method for checks during the run. See what a CMM report is for what to ask for.
A practical inspection plan
- Mark each critical dimension on the drawing and assign a measuring tool.
- Measure first-off parts fully after every set-up.
- Check critical dimensions at a set frequency during the run and record the results.
- Measure a sample from each lot at final inspection, using a recognised sampling plan.
- Measure the instrument against a reference if results look odd.
Next step
We check measuring equipment and calibration during factory audits and measure samples at inspection. Read what tolerances Jamnagar suppliers can hold for context. To plan inspection for your parts, book a free sourcing review.