Dial Indicators For Toolmaking
The use of dial indicators in precision measurement 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.
There are so many ways to use a dial indicator to ensure accuracy that working
without one would seem almost impossible.
Dial indicator applications
To align workpieces in a machine, such as a lathe, milling machine, EDM, or
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
Compare heights of various components on a granite surface plate
Mounting in a magnetic dial indicator base to check work on a surface
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.
Types of dial indicators
For injection mold makers, tool and die makers and precision machinists there are
essentially two types of indicators.
Test indicators are the ones that look like the face of a
watch with a needle out one side. Some of the more popular brands are Interapid, Fowler, Starrett,
Mitutoyo, Federal, Mahr, and 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
Test 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 gage 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!
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
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