Nyuck, Nyuck, Nyuck!
- 18 Jun 2006
- Reaction score
- Saskatoon, SK., Canada
Like everything in industry there are standards you do things to. Part of our job as inspectors in the aerospace machining plant was to calibrate the measuring tools used to make and inspect the parts with. We had our own procedures for calibration and the acceptance/rejection criteria was part of that. At one time some of it was based on an old US military specification which was superseded but the vernier calipers were acceptable (forgive me if I am off a touch as it has been a couple decades since reading it) if they read within +/- 0.001" for the first inch and were allowed an additional 0.003" total for up to 6" and then 0.001" for each inch of length after. So a 6" caliper could read 0.004" and still be within calibration and acceptable. You have to also understand that calipers are considered a coarse measuring tool in a machine shop and only used for rough or loosely tolerance work. If you were at the upper or lower end of the readings you went to better tools for acceptance or rejection. Micrometers are used when accuracy is demanded. What you shouldn't confuse is the resolution on the instrument as being the accuracy. The digital readout may be capable of displaying to 3 or more decimal places but that doesn't mean it is accurately measuring it. For pretty much everything you are going to do in a home wood shop they are more than good enough so don't loose sleep over it.Hi Gerry
Can you explain why that is so please?
I thought resolution referred to the the smallest step that could be resolved which for these is per the 0.1mm graduations on the dial as the instrument measures continually (i.e. the dial doesn’t jump in 0.4mm increments)
I think in the link RS quote 0.4mm accuracy, although in practice they (or the ones I have at any rate) are very much better than that, I wonder if it should be 0.04mm.