0015// Parallelism Measurement

According Y14.5-2009, 6.3.2 Parallelism,

Parallelism is the condition of a surface or feature’s center plane, equidistant at all points from a datum plane; or a feature’s axis, equidistant along its length from one or more datum planes or datum axis.

Basically, there are six possible cases for parallelism measurement:

1. surface parallel to datum plane

2. feature's center plane parallel to datum plane

3. surface parallel to datum plane (datum feature 's center plane)

4. feature's axis parallel to datum plane

5. feature's axis parallel to datum axis

6. surface parallel to datum axis

Case 1: Parallelism measurement for surface parallel to datum plane

Equipment needed to measure parallelism:

1. Dial indicator

2. Granite table

Case 2: Feature's center plane parallel to datum plane

In the drawing,

Equipment needed to measure parallelism:

1. Dial indicator

2. Block gauge

2. Granite table

Pass criteria:

Full indicator movement equal or smaller than size of parallel tolerance zone.

Side note:

The reason why only can travel distance L because block gauge only transfer points along distance L of the center plane's orientation information to the measurable surface.

Case 3: Surface parallel to datum plane (datum feature 's center plane)

In the drawing,

Equipment needed to measure parallelism: 1. Dial indicator 2. Engineers Parallels

Pass criteria: Full indicator movement equal or smaller than size of parallel tolerance zone.

Case 4: Feature's axis parallel to datum plane

In the drawing,

Equipment needed to measure parallelism:

Only Coordinate Measurment Machine (exact measurement) or Functional Gauge (pass/fail)

Case 5: Feature's axis parallel to datum axis

In the drawing,

Equipment needed to measure parallelism: Only Coordinate Measurment Machine (exact measurement) or Functional Gauge (pass/fail)

Case 6: Surface parallel to datum axis