In many articles presenting examples of control tools, we talk about controls by indicator clock. But what is a dial indicator? And how it works?
The function of an indicator, or dial indicator, is to make comparisons of measurements between two objects in order to check the conformity of one of the two objects, the second being the reference.
The dial indicator can be used
- in manufacturing processes, to check the flatness of a piece before machining it.
- in metrology, to check the dimensional conformity of a piece. In this case, the dial indicator watch is used together with a control tool, whose function is to position the piece.
- To explain the operation of a dial indicator, we will use the case of a dial indicator used in metrology.
The way we will use a dial indicator
- A dial indicator is composed of a series of mechanisms (1) contained in the plastic box that makes up the top part of the dial indicator and connected with an axis (2), finished by a spherical or flat tip (3) that will come into contact with the piece to measure. A spherical tip will be chosen for the measurement of a flat area, and a flat tip for the measurement of a zone with a curve.
- As its name indicates, the dial indicator allows obtaining information about the dimensional conformity of a piece comparing the measured point with a theoretical point, considered as perfect.
- In a control tool, the dial indicator is positioned in a dial indicator tower. In the example that we can see below, the control tool has two control points per dial indicator, and each dial indicator is positioned in a tower.
- The dial indicator tower positions the dial indicator at a certain distance from the piece to be measured, in general, 33 or 40mm.
- This distance is what we will compare with a theoretical point. In a control tool, this point is the tare tower. The tare tower has a height representing the exact distance between the dial indicator and the piece.
- In our case, if the distance is 33mm, the tare tower will have a height of 33mm.
- Before making any measurement, the dial indicator is reset to zero by inserting it into the tare tower and pressing the reset button, called “Origin” on many models.
- Once the comparing clock is zeroed, it is inserted in the dial indicator tower, to compare the theoretical distance represented by the tare tower with the real distance existing between the piece and the dial indicator.
- If the real part corresponds perfectly to your CAD, the screen will indicate “0”. If the piece is smaller than in the CAD, the dial indicator will indicate the difference: we will have a negative value.
- If the real part is larger than in the CAD, we will obtain a positive value.
- A piece is compliant if all its control points per dial indicator have values included within its tolerance range. For example, if the part has a tolerance of ± 0.5mm, all control points must have values between -0.5mm and + 0.5mm.
- According to the models, the dial indicator will indicate the deviations of the piece up to the hundredth or even the thousandth of a millimeter. There are also models indicating deviations in inches.
- To see a practical example, I invite you to watch this video of a control tool with dial indicator points. You will see that at the beginning of the video, the dial indicator clock is mounted on the tare tower.
I hope this explanation has been useful for you.