Please see video for further description. BORE GAUGE ISSUE - NEED HELP - YouTube
This might be a case of buy nice or buy twice, but here goes. Bore gauge set to 1.000 using micrometer. Double checking with gauge ring, reading shows 1.0015. I have double and triple checked everything. I have narrowed down that the centering feet cause 0.0011 error leaving about a .0004 error. I have no idea where this is coming from. Need help on why this is happening. Please watch video for a better understanding.
Iāve never heard of this before Iāve used bore gauges, internal mic, telescoping gauges and have only had error with telescoping gauges.
in regards to the smaller discrepency, after you tied the centering āfeetā back, is due to the dial gaugeās built in accuracy tolerance. Take a deeper dive into dial gauges - especially less expensive ones. Dials typically will specify three 3 +/- tolerance over its given range of travel:
- over-all range accuracy (on cheap dials this can easily be +/-0.0008".)
- repeatability accuracy (again, Iāve seen Chinese dials spec +/-0.0002")
- adjacent error (if one graphs the dials indicated reading of the entire range, it will not be a smooth linear line - instead, most will have ragged steps, indicating a gain or loss vs actual distance. For example, even with my very nice Mitutoyo bore gauge, the accuracy graph
in itās spec sheet indicates it loses 0.1Āµm at 0.2 mm travel, jumps tp a gain of 0.2 Āµm at 0.4 mm, and reads 0.25 Āµm low at 0.9mm travel. Iāve seen some Chinese dial indicators with 10x this deviation. To test your indicators error, measure/comparing setting with at least 3 different gauge ring sizes.
By the way, we do automotive engine work in my shop, where +/- 0.0001" can make a diff - finding a good bore gauge can be difficult, and keeping them accurate is a never ending
effort. 
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