Dial indicators are used in many types of service jobs. They are particularly useful in determining run-out on rotating shafts and rotors. Dial indicators can measure with an accuracy of 0.001" or 0.01mm. The objective of this procedure is to show you the correct method of measuring using a dial indicator.
Part 1. Preparation and safety
- Demonstrate the correct method of measuring using a dial indicator.
Whenever you perform a task in the workshop you must use personal protective clothing and equipment that is appropriate for the task and which conforms to your local safety regulations and policies. Among other items, this may include:
- Work clothing - such as coveralls and steel-capped footwear
- Eye protection - such as safety glasses and face masks
- Ear protection - such as earmuffs and earplugs
- Hand protection - such as rubber gloves and barrier cream
- Respiratory equipment - such as face masks and valved respirators
If you are not certain what is appropriate or required, ask your supervisor.
- Make sure that you understand and observe all legislative and personal safety procedures when carrying out the following tasks. If you are unsure of what these are, ask your supervisor.
Points to note
- Dial indicators are used in many types of service jobs. They are particularly useful in determining run-out on rotating shafts and rotors.
- Run-out is the side-to-side variation of movement when a component is turned.
- Dial indicators normally have two separate scales. The needle is able to move numerous times around the outer scale. One full turn may represent 0.1" or 1mm. The small inner scale indicates how many times the outer needle has moved around its scale. In this way, the dial indicator is able to read movement of up to 2" or 1cm.
- Dial indicators can measure with an accuracy of 0.001" or 0.01mm.
- The type of dial indicator you use will be determined by the amount of movement you expect from the component you are measuring.
- They must be fitted so that there is no movement between the dial indicator and the component to be measured.
- Most dial indicator sets contain various attachments and support arms so they can be attached to the component. There are other attachments available. These attachments allow the dial indicator to be configured specifically for the measuring task.
- When attaching a dial indicator, keep support arms as short as possible. Make sure that all attachments are tightened to prevent unnecessary movement between the indicator and the component.
- Make sure the dial indicator pointer is positioned at 90º to the face of the component to be measured.
- Always read the dial, face or straight on. A view from the side can give a considerable "parallax" error. Parallax error is a visual error caused by viewing measurement markers at an incorrect angle.
- The outer face of the dial indicator can be moved so that the zero can be positioned over the pointer.
Part 2: Step-by-step instruction
- Select the correct gauge and attachment
Select the gauge type, size, attachment and bracket, which fit the part you’re measuring. Mount the dial indicator on a firm surface to keep it still.
- Ensure plunger is at 90 degrees
Adjust the indicator so that the plunger is at 90 degrees to the part you’re measuring.
- Press the plunger halfway in
Press the dial indicator gently against the part, and rotate the part –in this case a brake rotor-- one full turn. Keep pressing until the plunger settles about halfway into the indicator.
- Lock into position
Lock the indicator assembly into position.
- Rotate and read
Carefully rotate the brake rotor a couple of times, while you observe the dial readings face on.
- Record any movements
If the pointer hovers around a single graduation on the dial, the part has minimal run out, or surface distortion. If it moves significantly left and right, you should note these variations. Find the point of maximum movement to the left and move the dial so that zero is over this point. Continue to rotate the brake rotor. Find the point of maximum movement to the right, and note the reading. This will indicate the run out value. Continue this rotation several times to confirm the points of maximum variation.
- Check your results
Check your readings against the manufacturers specifications. If the deviation is greater than the specifications allow, consult your supervisor.