Dial Test Indicators

We’ll start this blog with a picture of a standard dial test indicator:

Looks relatively simple.  But now take a look at the same indicator with the side cover removed:There’s an awful lot in there.  And we haven’t even gotten to everything inside the head itself:

Here’s what’s happening:  You move the needle, which moves an arm, which has teeth on the other end, which move a crown gear, which moves a pinion gear, which moves the needle (and sometimes another gear, which moves another needle).  It’s worse than the house that Jack built.  What’s really amazing is that some test indicators are accurate to plus-or-minus fifty millionths of an inch.

So, take good care of your test indicator.  Don’t plunge it into a mill’s work surface, and don’t spin it up in a lathe.  We can fix it, usually.  But it will usually cost a lot.


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