Dial Test Indicators

Dial Test Indicators

Dial test indicators are similar to dial indicators, but are typically more precise and have a smaller range of movement. Rather than a plunger that moves in and out, they have a small lever arm with a ball-shaped tip that moves up and down. This enables the tip to be inserted into a small hole so that the hole can be precisely centered on the lathe axis - an operation that could not be done with a dial indicator.

The indicator shown here has a measuring range of 0.030 - much less than a dial indicator - and reads plus or minus from the zero point. When the tip is at rest at its neutral point, it can be moved 0.015 in either direction. The tip can be set at different angles for convenience in setup. As on the dial indicator, the bezel and numeric scale can be rotated to zero the reading. Each division is 0.0005 (5 ten-thousandths or half a thousandth per division).

Here's a photo showing the DTI in use centering a bolt with a hole drilled in in in the 4-jaw chuck. You could not use a DI in this situation since there is no exposed surface of the bolt other than the hex head. Instead, we take the reading off the edge of the hole, taking advantage of the narrow ball tip of the DTI. Since the DTI has only a very limited range, you must have the bolt pretty nearly centered already before you can use the DTI. You can get pretty close by observing how far each jaw extends from the edge of the chuck and making these as nearly equal as possible.

Dial Test Indicator

Probe indicators

Probe Indicators
Probe indicators typically consist of a graduated dial and needle to record the minor increments, with a smaller embedded clock face and needle to record the number of needle rotations on the main dial. The dial has fine gradations for precise measurement. The spring-loaded probe (or plunger) moves perpendicular to the object being tested by either retracting or extending from the indicator's body.

The dial indicator face can be rotated to any position, this is used to orient the face towards the user as well as set the zero point, there will also be some means of incorporating limit indicators (the two metallic tabs visible in the right image, at 90 and 10 respectively), these limit tabs may be rotated around the dial face to any required position. There may also be a lever arm available that will allow the indicator's probe to be retracted easily.
Dial Indicator

Dial Indicators Applications

Dial Indicators Applications

Dial Indicator are applied to various activities as follow :
* To check for runout when fitting a new disc to an automotive disc brake. Runout can rapidly ruin the disc if it exceeds the specified tolerance (typically 0.05 mm or less).
* In a quality environment to check for consistency and accuracy in the manufacturing process.
* On the workshop floor to initially set up or calibrate a machine, prior to a production run.
* By toolmakers (moldmakers) in the process of manufacturing precision tooling.
* In metal engineering workshops, where a typical application is the centering of a lathe's workpiece in a four jaw chuck. The DTI is used to indicate the run out (the misalignment between the work piece's axis of rotational symmetry and the axis of rotation of the spindle) of the work piece, with the ultimate aim of reducing it to a suitably small range using small chuck jaw adjustments.
* In areas other than manufacturing where accurate measurements need to be recorded (e.g., physics).
Dial Indicator

Dial Indicators General Specifications

Dial Indicators General Specifications
There are several variables in dial indicators:

* Analog versus digital/electronic readout (most are analog)
* Dial size. Typically referred to be American Gage Design Specification (AGD):

AGD Diameter range (in) Diameter range (mm)
  • 0 1–1 3/8 25–35
  • 1 1 3/8–2 35–50
  • 2 2–2 3/8 50–60
  • 3 2 3/8–3 60–75
  • 4 3–3 3/4 76–95

* Accuracy
* Range of travel
* Number of dial revolutions
* Dial style: balanced (e.g., -15 to 0 to +15) or continuous (e.g., 0 to 30)
* Graduation style: positive numbers (clockwise) or negative numbers (counterclockwise)
* Revolution counters, which show the number of revolutions of the principal needle.
Dial Indicator

Dial indicators

Dial Indicators
Dial indicators, also known as dial gauges and probe indicators, are instruments used to accurately measure small linear distances, and are frequently used in industrial and mechanical processes. They are named so because the measurement results are displayed in a magnified way by means of a dial.

A special variety of the dial indicator is the dial test indicator (DTI) which is primarily used in machine setups. The DTI measures displacement at an angle of a lever or plunger perpendicular to the axis of the indicator. A regular dial indicator measures linear displacement along that axis.

Dial indicators may be used to check the variation in tolerance during the inspection process of a machined part, measure the deflection of a beam or ring under laboratory conditions, as well as many other situations where a small measurement needs to be registered or indicated. Dial indicators typically measure ranges from 0.25 mm to 300 mm (0.015 in to 12.0 in), with graduations of 0.001 mm to 0.01 mm (metric) or 0.00005 in to 0.001 in (imperial).