Indicators

There are two basic types of indicators:  Dial, and dial test (sometimes called a finger gage).  This time we’ll talk just about dial indicators.  They work essentially like a dial calipers, except that the rack moves across the gears rather than the gears across the rack.

If you remove the back of an indicator, it will probably look something like the first picture below .  You can see where the rack (the vertical steel rod) meets a small pinion gear just right of center, near the bottom of the housing. 

The next four shots, starting from top right, give a clear view of the rack’s teeth; the pinion itself (as well as the larger gear attached to the pinion); the gear to which the needle is attached; and the backlash spring with its gear beneath it.  You’ll have to zoom in pretty close to see some of the gears.  But it’s easy to understand why they all need to be free of chips and dirt, as well as having no broken or missing teeth.

Indicators can be tricky and difficult to work on, so we suggest you give us a call if you have trouble with one.  But hopefully, this posting will help you understand how they work.

Next time:  Dial test indicators.

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