VTube-LASER End Point Deviations

This page describes how to find the END POINT deviations. Back to VTube-LASER

Three Main End Point Deviations

There are three main end point deviation values calculated during an alignment of the MEASURED to the MASTER tube.

END LENGTH Deviations

The end length deviations are found at the top of the Inspection menu. These deviations show you how much to trim a part to make it fit within the current alignment better.

AFTER-TRIM Deviations

These are found in the first T1 value and the last T2 value in the Tangents grid. These deviations show the expected radial deviation if the tube were trimmed.

How to Understand the End Point Deviations

Automatic Internal Trimming of End Points for Shape

Even though the end points are not tangents, we can still use them in the chart because they qualify the part the same way that tangent points do. A key in understanding the T1d of straight one and the T2d of the last straight is to remember that the deviation is not the same as how long or short the straights are relative to the master tube shape. See the illustration on the right to understand why. The MASTER to MEASURED end point deviation in the Tangent grid is 1.9mm. The measurement is the distance between the two lines at the corresponding end points - as if the MEASURED WERE TRIMMED. (The Measured part is the pink part. The Master part is white.)

Untrimmed End Points for Lengths

However, the end length is 90.2mm too long. In this application, the customer bent the part 90mm too long on purpose in order to give the bend arm clamp die enough material on the first straight to grip. Notice that, even though the part is significantly too long, the BEST FIT algorithm didn't use the actual measured end point in the alignment. The alignment was based on the trimmed point on the measured centerline that was nearest the master end point. So, in this case the part shape in space is qualified - but it needs trimming by 90.2mm to also qualify the end length (another critical qualifier).

Typical Industry Tangent Point Tolerances

In working with thousands of customers over the past few decades, we've seen some trends in accepted envelope deviation tolerances. Here are what we commonly see: Aerospace and Automative Fluid Lines Diameter Range Envelope Tolerance 12.7 mm (0.5 inch) diameter tubes or less +/- 1 mm (0.039 inches) Greater than 12.7 mm (0.5 inch) +/- 2 mm (0.078 inches) Automotive Exhaust Pipes Diameter Range Envelope Tolerance 50 mm to 76 mm From +/- 2 mm to +/- 3 mm 76 mm to 102 mm +/- 3 mm Larger then 102 mm +/- 3 mm or greater Shipbuilding Diameter Range Envelope Tolerance All Diameters +/- 6 mm HVAC Diameter Range Envelope Tolerance All Diameters +/- 2 to +/- 3 mm Structural Tubes (Frames) Diameter Range Envelope Tolerance All Diameters +/- 2 to +/- 3 mm Tighter Tolerances Sometimes customers will required +/-0.75 mm - but this is very rare. We've never seen tube shapes that must be qualified with a deviation tolerance of less than +/- 0.75 mm.

Other Pages

• See also VTube Intersection Point Tolerances
• Back to VTube-LASER