Dial Indicator

[Speedy Builder5Participant @speedybuilder5]

Mitutoyo  513-118. (inch)

I have a working one of these indicators.  It has three probes with different ball end sizes, but the smallest one is substantially longer than the other 2 (which indicates differently to the other two).  I haven’t stopped to measure the difference, but has anyone a reason for this ?

Bob

[Clive FosterParticipant @clivefoster55965]

The longer probe is used when needing to indicate off a point that the shorter, standard probes can’t reach.

Trade off for longer reach is reduced sensitivity. Reduction is by the ratio of probe lengths when measured from centre of pivot to contact point on the ball.

These devices are zero point detectors not true measuring devices. Inherently prone to cosine error depending on the angle of the probe arm centre line to the contact point on the workpiece. Verdict use a pear shaped contacting end rather than ball which, allegedly, correctly compensates for such cosine errors. In practice the correct use is to determine the deviation from zero as the job moves. So long as the indicator today and probe are in a straight line the scale calibration error is negligible about the centre off indicator needle rotation ie 0 on the dial with indicator in bi-directional mode. The Verdict tip is remarkably good at error correction even when probe and body have significant offset angle.

In practice almost no needle flicker is good enough for folk like us unless its real special job.

My workhorse is a 1″ dial, 1 thou sensitivity Verdict. I do have a tenths thou version for special jobs to be used only after appropriate meditation and achieving serene tranquility. Which state sometime lasts long enough to get stuff set-up! Sometimes.

Clive

[old martParticipant @oldmart]

I use the lever type indicators all the time for zeroing runouts in chuck held work and similar, the actual measurement is not important, when striving for a zero movement of the dial so angle and length if the arm can vary. If you do want to have an actual reading, the only way would be to first mimic the setup to be used and check with slip gauges to find the error in thedial readings.

An extreme example of the error would be using a coax indicator for setting up a boring head in a mill. The indicator has divisions on the dial which are meaningless seeing the huge variety of lever lengths and shapes they need to reach the surface of the workpiece. The numbers do not matter as the indicators are set when the needle stops moving wherever it is pointing.

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