Because the coordinates for parallelism error depend on the position of the part relative to gage components, some operators may find this confusing. This post helps clarify some common questions you may have about parallelism. First, we define Parallelism, then we discuss the coordinate system.

Definition
Journal parallelism is based on the radial measurements of the two outside cuts of the journal. The calculation compares the Least Squares Center (LSC) of cut 3 to the LSC of cut 1 to determine the axis of the specific journal and then compares this journal axis to the reference axis. The reference axis, or datum, is based on the average center components of the outside cuts (cut 1 and cut 3) of the reference journals. The reference axis is normally the end journals or adjacent journals, but it could also be the gage axis or a specified axis based on selected journals. In some gage models the reference axis can be redefined.

Journal parallelism can be affected by the journal width, or the distance between the outer cuts. Parallelism is not affected by the journal radius. Linear scan data can be analyzed relative to a part axis to provide an alternative parallelism calculation.

Output Options
Once journal parallelism has been measured, you can view the output error in two different ways— as absolute parallelism values, including the angle at which it occurs, or as X and Y parallelism values. The first method gives the vector component of the parallelism; the second method gives the individual components of the parallelism.

System of Coordinates

Adcole has specified the system of coordinates for current versions of software as follows —the y-axis is in line with the follower motion as it extends and the x-axis is perpendicular to this follower travel.

When viewing from the axis of rotation positive x moves from the axis of rotation into the stone, positive y moves from the axis of rotation into the follower.

The coordinate system is the same when a crankshaft is measured in a counter-clockwise rotation or in a clockwise rotation.

The orientation of the part is with Main 1 at the headstock end and Main N at the tailstock end.

Inverted Parts
Though inverted parts vary physically in how the system of coordinates appear, your output results remain consistent regardless of the part orientation in the gage. Inverted parts are measured rotating in the opposite direction of rotation as when the part is placed in the gage with main 1 at the headstock. The software takes this information into account when calculating parallelism and reports identical output.

Use Caution When Measuring Parallelism
Parallelism can be influenced by issues with the part centers
Parallelism can be influenced by Driver issues

If you have questions about parallelism or our other measured features, please contact Adcole at 1 800 858 5802 or [email protected]