What are Centerline Tangent Points and Why Are They Important in VTube-LASER?

Reading the T1d, MP, T2d Chart Back to VTube-LASER

How to Understand the Chart

The chart is represented by a grid of straights for each row, and critical inspection points along each straight: T1d = Tangent 1 Deviation MPd = Midpoint Deviation T2d = Tangent 2 Deviation Technically a tangent point is the point where the straight meets the bend. These are considered the best points for qualifying a tube shape because they most closely approximate a profile gauge. The only exception are the points at the end - where no bend is attached. But these points (T1d in straight 1, and T2d in the last straight) still have value in determining if the part is the correct shape. If the tangent points are within tolerance, then it follows that the shape of the part - based on the straights - fits well enough inside the restricted path or envelope in order to qualify. In GD&T, this is often referred to as the centerline profile.

How to Set the Tolerance

You can set the tolerance in two places in VTube. One place is in the System Options / Measure 2 menu.

The second place to edit the value is in the VTube-LASER Measure Setup menu's "Other" tab menu.

Choosing Values

A tight qualification is 1 millimeter. It is much more challenging to measure the end scan with a tight tolerance. Keep in mind that tube deformation will make tight tolerance end scans more challenging. A much easier / quicker qualification is to increase the value to much high number - like 25 millimeters. (Many customers use 25 millimeters to avoid this qualification from occuring completely - and making end scans much easier.)

Set the Default

Set the default value by clearing the VTube project, then changing the value, then saving the setup to the default file in the System Options - Project Setup menu.

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