It Measured Wrong.
When parts measure out of tolerance, the first step is confirming that both parties are measuring the same way from the same datums, because measurement disagreements account for a substantial share of rejections.
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- 337-837-2314
When parts measure out of tolerance, the first step is confirming that both parties are measuring the same way from the same datums, because measurement disagreements account for a substantial share of rejections.
The parts arrived, you measured them, and they do not meet the drawing. Before anything is scrapped or returned, it is worth establishing whether the parts are wrong or the measurement is — and that is not a defensive question, it is the fastest route to a fix.
What to do
- 01
Check you are measuring from the same datums
If the drawing does not clearly establish datums, two people can measure the same part correctly and get different answers. This is the most common cause of a measurement dispute and it is a drawing problem, not a machining one.
- 02
Check the instrument suits the tolerance
A caliper is reliable to about a thou. Using one to reject a part toleranced in tenths measures the instrument, not the part.
- 03
Check the temperature
Steel expands measurably with temperature. A part measured warm off a truck in summer, or held in a hand for a minute, will not read the same as one at 68°F. On tight-tolerance work this alone can account for the difference.
- 04
Ask for the inspection record
A shop that recorded a first article and in-process checks can show what the parts measured before they shipped, and on what equipment, with what calibration status.
- 05
Then decide the disposition
If the parts are genuinely out, the options are rework, replacement, or use-as-is by written agreement. All three should be recorded rather than settled verbally.
Questions People Ask
What should I do if machined parts measure out of tolerance?
- Confirm first that both parties are measuring from the same datums with instruments appropriate to the tolerance, and at a stable temperature. A large share of rejections turn out to be measurement disagreements. If the parts are genuinely out, agree a disposition — rework, replace, or use-as-is — in writing.
Can temperature really change a measurement?
- Yes. Steel changes size measurably with temperature, which is why precision inspection is done at a standard temperature. On parts toleranced in tenths, holding the part in your hand is enough to shift the reading.
Send us the part.
337-837-2314 — or send photographs and we will tell you what we can do.