The dial indicator is an invaluable tool in our engineering workshop. It is an indispensable instrument that we use every day. For us, the most common application is for truing up various cylindrical materials in a 4-jaw lathe chuck prior to a machining operation. On any typical day, we'll be working with mild steel, stainless, aluminum, brass or an assortment of plastics. The dial indicator setup procedure is the same in all cases.

Once the cylindrical material is centered by eye as accurately as possible (the grooves in the 4-jaw chuck will help with this) the job can be quickly and perfectly centered with a dial indicator (D/I) using the following technique:

* Position the D/I in a convenient place on the lathe (our D/I has a magnetic base) and make sure the plunger (also known as the probe or spindle) of the instrument is within the dial range - depressed against the workpiece.

* Now, spin the chuck by hand through 360 degrees and make note of the highest and lowest readings. When you add those two numbers together and then divide the total by 2 you will get an average reading of the runout that needs to be corrected. Make a note of that reading.

* Slowly revolve the chuck again until that average reading is showing on the dial - then zero the dial face to that position.

* Now turn the chuck again until one of the jaws is in line with the dial indicator's plunger, and adjust the jaws until the zero position shows on the D/I needle.

* Turn the chuck 180 degrees so that the opposing jaw is now in line with the D/I. As above, adjust this jaw until the needle zeros on the dial.

* The next step is to spin the chuck by hand 90 degrees and repeat the above 'zero positioning' procedure for the remaining two jaws.

That simple technique can often get the job perfectly centered - first time. If some adjusting is still required you can fine tune the centering with a little pinching and slackening of the chuck jaws. If necessary, you can repeat the previous steps to get a new, finer average of the runout and then reset the jaws as described above - but more often than not, a tiny adjustment of the chuck jaws will sort it out.

The dial indicator is also known as a probe indicator or dial gauge. A specialized variation of the D/I is the dial test indicator. (DTI) This instrument is sometimes called a finger indicator or a lever arm test indicator, or simply a test indicator. The DTI is used mostly in machine setups. It has a smaller and usually more accurate measuring range than the D/I. A typical dial indicator will have a 1 inch range and will be calibrated in increments of 1000th's of an inch.  A DTI on the other hand will typically have a much smaller range but is capable of finer measurements (0.0001" - 0.00005")

The following images show the  difference in construction between a standard Dial Indicator and a Dial Test Indicator:

dial-indicatordial-test-indicator

There are many pre-used and brand new dial indicators for sale online today. If any of these items catch your interest, just click the links below for more information:

There are many manufacturers of dial indicators supplying the market today. Among them are
Starrett, Fowler, Mitutoyo, Moore & Wright, Browne & Sharpe, Mahr/Federal Inc, and Blake Manufacturing