321 Plane Line Point Aligment

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Vtube-laser logo 1.96.png This page explains the 321 Plane Line Point alignment.

Vtl screen hd scanner without logo.png


What is Alignment?

"Alignment" refers to the process where the measured tube is being aligned to the master tube.

TThere are different ways to align a measured tube. 321 Plane Line Point is a common alignment method used for situations where you want to give extreme weight or emphasis to one section of the tube during alignment.

321 Plane Line Point

The alignment is pronounced "three two one plane line point".

This alignment method requires:

  • 3 Plane Points

  • 2 Line Points

  • 1 Translation Point

Illustration of how 321 PLP Works

The 321 Plane Line Point alignment method is much less sophisticated than the other iterative Best Fit aligment algorithms.

There are three steps in the alignment process:

  • STEP 1 - Align the part so that 3 point plane selected in the measured part aligns perfectly with the same 3-point plane in the master part.

VTL compare master and measured LRA.png

Visually Demonstrate the Problem of Qualifying with Angles

Unless you can perform 3D trigonometry mentally on-the-fly, the answer to the question above isn't obvious. Even if we guess the answer, we can not accurately guess at what tolerance envelope value the part would be considered acceptable.

It's easy to visually demonstrate the limitation of using bender data to tell us if a part shape falls within the tolerance envelope.

Compare the two similar parts and their alignments. The image on the right is from the alignment of the two tubes from the LRA data shown in the report above. The white tube is the MASTER. The pink tube is the measured. The blue transparent cylinders that surround the tube are the TOLERANCE ENVELOPES. The tube shape must be within each straight's tolerance envelope to be considered a good shape - or a shape that qualifies.

This first part has 4 inch straights for every straight. (See the LRA data above.)

All the centerlines fall within within the tolerance envelope. The "T1 dev" column values are TANGENT 1 DEVIATIONS, and the "T2 dev" column values are TANGENT 2 DEVIATIONS.

The tangent points are where the straights meet the bend arcs along the centerline.

VTL image 4 inch straights.png

This second alignment image shows the part with IDENTICAL ANGLES - but the two middle straights are lengthened to 10 inches between bends.

You can see red cells in the Tangent point/Midpoint grid, and yellow tolerance envelopes where the pink is breaking through.

The part is no longer within tolerance - even though all the angle deviations are identical between the two parts.

VTL image 4 inch and 10 inch straights.png

The Best Data for Qualification

The best data for qualification is centerline TANGENT POINT and MIDPOINT data in the Inspection Data menu and in the Reports menu.


For more information, see What are Centerline Tangent Points and Why Are They Important in VTube-LASER?


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