Repairing dial indicators is a task usually assigned to a trained gage technician. Because the indicator amplifies the actual gage displacement to make it a readable value, it is an essential component.
While designed for the shop floor, mechanical indicators and comparators are delicate instruments that must be handled with care and have their performance checked regularly. An indicator may become faulty or go out of calibration for any number of reasons. In such cases, users rely on their preferred repair center to fix the indicator and verify its performance.
When time is not an issue, users typically choose between two levels of repair service. The first is “repair to working” condition. Many repair centers clean the indicator, inspect the its components and may re-orient internal parts from a used indicator to get the gage working. The calibration is then verified and the indicator returned to the application. In many cases, this is a sound method of indicator repair. However, service warranties may be limited—if they are provided at all—and the gage should be continuously monitored for repeat performance.
One option is to have the indicator repaired by the manufacturer or by an a factory authorized repair center. This option is initially more expensive, but is a better value over the life of the indicator. Manufacturers can repair the indicator to a “like new” condition, often substituting a complete new movement rather than spending time looking for a worn component. Because only original manufactured new components are used, the indicator is recertified and returned with a warranty of service, just as if it were a new indicator.
However, there are times when things don’t go as planned. For example, when an indicator gets stuck at a critical moment and just won’t work. At times like these, it may seem like the weight of the world is coming down, but fear not: most indicators manufactured in the past 50 years are able to be repaired. With some care and foresight, many indicator problems can be repaired in a pinch—at least, they can be fixed well enough to get you through the process, or until a replacement can be brought in to take the place of the suspect indicator.
The symptoms of a sick indicator can vary significantly, but the most common is a stickiness in its travel. An indicator can get so stuck that when the rack is pushed in, it simply does not return. As I have said many times before, dirt is the probable cause, and it may be time for some good housecleaning.
But first take a look at the indicator in general. Is anything missing, or do you see any physical damage? Could the stem be bent and not 90 degrees to the case? Or perhaps a rack is bent. Or a stem is pinched from a too tight clamp. If any of these is the case, there is probably not much you can do: It’s time for some professional repair or even a new indicator.
If things look OK from the outside, go ahead and remove the indicator's back. Then remove the bezel clamp and the bezel. Some bezels snap on, while others have screws that need to be loosened. Once the guts of the indicator are exposed, look for dirt, oil, floating broken gear teeth or pieces of a jeweled bearing. In the latter cases, it’s again time for a professional.
However, if the interior just looks dirty or oily, splash alcohol around on the inside of the case until the gears and the rack are completely soaked. Work the rack up and down to work out the contamination. Most times, you’ll begin to feel a significant difference in the action of the indicator. Repeat the process again and use a little compressed air to blow out the case and dry off the movement. If this routine has eliminated the stickiness, you just might be in business. Put the bezel and clamp back in place and then attach the back, being careful not to over-tighten the back screw, which may distort the case.
Before you put the indicator back on the job, run it through its paces to see if it’s measuring properly. Mount the indicator in a stand and get some gage blocks that are spaced so that they cover the range over which the indicator will be used. Zero the gage, and start checking the gage blocks. Or, if there is a micro-calibrator available, check the indicator through its full range in both directions. If the indicator is measuring properly (usually to within a grad), congratulations—you’ve saved the day. Put the gage back to work, watch it carefully and schedule a check-up with the professionals at your earliest convenience. With a good, professional repair, that indicator should be ready for another 100,000 cycles.