Accurate measurement

[norman valentineParticipant @normanvalentine78682]

I use a dial caliper for most of my work, I find that it is accurate enough for me as long as I wipe the jaws each time I use it and pinch on the outside of the jaws to ensure that they close properly on the work. I find that they agree with my micrometers.

I used to use a Lidl digital caliper in the mistaken idea that repeatability not absolute accuracy was the most important factor. Then I realised that they don't score in either.

Edited By norman valentine on 09/02/2018 19:52:01

[I.M. OUTAHEREParticipant @i-m-outahere]

One thing micrometers have over calipers is repeatability as it is much easier to control the amount of pressure on the measuring surfaces with a device that uses a thread to control movement even more so if they have a friction clutch like a mic

For the OP try a little exercise – mount a dial indicator up on your lathe toolpost so it can take a reading of the saddle and compound slide movement , the nib shoud be in contact with the face of the chuck .

Now zero out the indicator and then move the carriage towards the chuck say .100 or 1mm depending in what measuring system you use and zero out again .

Move the carriage back a little then try to move it back into zero – you will find this difficult to do even with a carriage stop as there will always be some difference in the reading from zero .

Next lock the carriage and do the same procedure using the compound slide ( make sure its travel is parralell to the bed of the lathe ) you will find you can easily bring the dial indicator back to the pre set zero .

That is the difference between a straight linear movement and a linear movement controlled by a thread .

A caliper uses straight linear movement and a mic uses a linear movement controlled by a thread which really works a bit like a gear ratio .

[HOWARDTParticipant @howardt]

At what temperature do you all measure. Instruments are only accepted as true indicator in controlled temperature environment. If you want consistency then you have to keep the work place constant, temperature doesn't matter so long as the calibration is done at that temperature.

[Michael GilliganParticipant @michaelgilligan61133]

Forgive me if this digresses too far from the original topic, but it may be of interest to some:

**LINK**

https://www.nist.gov/news-events/news/2016/02/thinking-outside-cuvette-measure-dimensions-skinny-glass-container-pml

MichaelG.

[Author]

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