Check machining capability in four steps: compare the machine list with your part, see those machines running, review the measuring equipment, and test sample parts. A machine list alone proves little. Capability is proven by parts that meet your drawing, measured with reliable instruments.
Ask for evidence at each step. A good factory is glad to show it. A weak one tends to stay general.
Match the machines to your part
Start with your drawing. What size is the part? What operations does it need: turning, milling, drilling, grinding, boring? What are the tightest tolerances and finest surface finishes? Then read the factory's machine list with those questions in mind.
- The machine's working envelope must fit your largest part with room for fixtures.
- The number of axes must suit the geometry, such as 4-axis or 5-axis work for complex shapes.
- Grinding or honing is usually needed for very tight tolerances and fine finishes.
- Spare capacity on the right machines tells you whether your order can be scheduled.
- The age and condition of the machines affect how well they hold accuracy.
See the machines running
Visit, or ask for a live video walk-through. Look for the specific machines on the list, running real jobs. Idle machines covered in dust are a warning sign. So are machines that seem to belong to a neighbouring workshop.
Ask what parts each key machine is running today and what tolerances they hold. Look at the parts themselves. Ask to see the setup sheet and program for one job.
Check the measuring room
A factory can only make what it can measure. Look for height gauges, micrometers, bore gauges, thread gauges, surface roughness testers and, for complex parts, a CMM. Check that instruments carry calibration labels with valid dates, and ask for calibration certificates from an accredited laboratory.
Match the instruments to your tolerances. A common rule is that the measuring device should resolve about a tenth of the tolerance. If your tolerance is very tight and the factory has only calipers, it cannot prove conformity.
Test with sample parts
The best evidence is your own part. Order a small sample batch and ask for a full dimensional report, as described in first article inspection. Measure the parts yourself or have an independent lab do it. If the results match, you have real evidence of capability.
For larger volumes, ask for a short capability study on critical dimensions. This shows whether the process can hold the tolerance consistently, not just once. For a list of equipment to expect, see what machines a precision supplier should have.
Next step
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