Moldmaking Resource Plastic Mold Makers, Mold Designers, Mold Repair Guide The use of a dial indicator as a precision measurement tool is universal and indispensable. No matter which CNC machine shop, injection mold making shop, or tool and die shop you visit, you see dial indicators in use everywhere.
Typical uses for the dial indicator
- To align workpieces in a machine, such as a lathe, milling machine, EDM, or surface grinder
- Check spindle runout in any machine tool.
- Align workpieces in a spin fixture, such as a Harig or Hardinge spinner
- Inspect workpieces in a grinding machine, such as a Ded-tru, or cylindrical grinder
- Compare heights of various components on a granite surface plate
- Mounting in a magnetic dial indicator base to check work on a surface grinder
- Mounting in a fixture to inspect work in a Bridgeport milling machine, or any other vertical machining center, 5 axis milling machine or high speed machining center.
- Analyze surface roughness
- Analyze EDM pit depth
- Compare injection mold parting line details
The list goes on and on because this inspection tool is so flexible and useful. With a minimum of set-up and fuss, a precision machinist or toolmaker can gain a wealth of knowledge about his part, be certain it is properly set-up and the right size.
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An authoritative book, The Metrology Handbook, Second Edition provides a foundation for understanding basic metrology and calibration principles and practices.
Types of dial indicators
For injection mold makers, tool and die makers and precision machinists there are essentially two types of indicators: test indicators and plunger type, or travel indicators. They are similar, yet distinctly different in application.
Dial Indicator Manufacturers
| Interapid | Girod | Starrett |
| Mitutoyo | Mahr | Tesa |
All of these are known for their quality and repeatability. It makes no sense whatsoever to buy a cheap imitation if you are doing serious toolmaking. You will only regret it in the end.
Dial test indicators
Test indicators are the ones that look like the face of a watch with a needle out one side. These indicators are extremely versatile and flexible. The dial is adjustable, the needle is adjustable, and some have a mounting shank that can also be adjusted. Together with a magnetic base or height stand, you can inspect almost anything in a modern machine shop.
It is necessary to have a flat, calibrated granite surface plate to ensure accurate readings with any dial indicator. The surface gauge must also be free from chirping, or making vibration sounds when moved across the surface plate.
The indicator must be stable and free from distortion. I have seen many that actually flex when you blow on them! Not much reliability there!
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An authoritative book, Basic Metrology for ISO 9000 Certification
gives a nice introduction to ISO 9001 requirements for calibration of test and measuring instruments.
Travel Indicators
Plunger, travel, dial or whatever you might call this style of indicator, it is a mainstay of manufacturing. These are used daily in a variety of applications.
Plunger type indicators are the larger ones that have a clock like face and a straight plunger out one side. These can either be mechanical or electronic. These have the advantage over test indicators in that they have much greater range, or travel. Most have at least 1 inch of travel, but they are available in longer lengths as well.
Plunger indicators are commonly used to monitor movement of parts. They are also used in production to monitor the registering of moving parts, such as in an injection molding machine.
A common tool room use is on the lathe. This is convenient for longitudinal travel along the ways of the lathe. Core pins, punches and long components are often made using a plunger type indicator.
Care of dial indicators
Dial indicator repair and calibration is very important. Over time, the tips become worn, the jewels worn and the face can become damaged. A trip to the dial indicator repair shop is a good investment. If your indicators are sticking and you don’t notice, you can easily produce a lot of scrap in a hurry!