Plastigauge - Abridged Specification for Plastigauge Products

Abridged specification
for Plastigauge products

1. Scope
2. Purpose
3. Method
4. Standard Calibrated Ranges
5. Accuracy
6. Applications
7. Materials
8. Conclusions

1. Scope
This specification has been prepared as a guide to users and potential users. Manufacturing dates have therefore been excluded.

2. Purpose
Plastigauge, Plastic Precision Clearance Gauges offer a simple but effective method for the direct measurement of clearance between hidden surfaces. Thay are particularily useful for measuring clearance in split or plain bearings or in engineering situations where direct measurements are inappropriate or where a feeler gauge cannot be inserted.

3. Method (see fig. 1)
Plastigauge comprises a rod or thread of compliant plastic material of accurately determined cross0section (either circular or square). The surfaces, between which measurement is to be made are separated, the Plastigauge is inserted as in fig. 1 (a), and the surfaces are returned to their standard postion, fig. 1 (b).

The once circular cross section will have been flattened but the area of the cross section will not be changed. We can therefore state that:

or in the case of square section gauges of side a:

Thus T, the clearance to be measured is equal to a constant divided by the width of the strip after deformation.

By opening the surface to reveal the deformed guage, W, can be measured directly and from this, T, the clearance, can be determined.
In practice, the need for this calculation is obviated by the use of a calibrated scale on which an array of marks has been printed (fig. 2) The strip width produced can be compared with the scale. The actual clearance is shown alongside the mark which most nearly corresponds to the width W. For greater discrimination the clearance may be interpolated between the two most nearly comparable scale marks.
A method which is commonly used for the measurement of clearance in automotive bearings is shown by fig. 5.

4. Standard Calibrated Ranges
Plastigauge, Plastic Precision Clearance Gauges are manufactured in lenghts of approximately 4" (100mm). Six standard sizes are available to cover the measurement of clearances from 0.0007 - 0.070".
The range is more fully described in the table below:

PL-A Plastigauge For measurements of 0.001" - 0.007" (0.025mm-0.175mm)

PL-B Plastigauge For measurements of 0.004" - 0.010" (0.100mm-0.250mm)

PL-C Plastigauge For measurements of 0.007" - 0.020" (0.175mm-0.500mm)

PL-D Plastigauge For measurements of 0.020" - 0.040" (0.500mm-1.00mm)

PL-E Plastigauge For measurements of 0.030" - 0.070" (0.75mm-1.75mm)

PL-X Plastigauge For measurements of 0.018mm - 0.045mm

5. Accuracy
Measurements by Plastigauge are inherently accurate as they are direct and this avoids the problems associated with the more conventional measurement techniques. For example, where clearance is to measured on a used bearing, it is inevitable that wear will be localized. Plastigauge will show the variation of wear across the bearing. When new bearings are being fitted Plastigauge will show the high spots- and by how much they are high.

The fundamental accuracy of Plastigauge is high. It is shown in Table 1 above. The accuracy achieved is use will be determined by additional factors such as the interpolation of the scales and the surface finish of the bearing (see fig. 3). In the latter case a micometer measurement would be optimistic and show the measurement across the high spots. Plastigauge measures the space available for lubricants to flow. which is more representative of the measurement required.

6. Applications
info to come

7. Materials
info to come

8. Conclusions
info to come