The Limitations of Qualifying Tube Shapes using Bender Data

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Vtube-laser logo 1.96.png This page explains the major limitations of using bender data for qualifying tube shapes.

Vtl screen hd scanner without logo.png


What is Bender Data?

Bender data is the data used to setup tube bending machines. Usually, bender data has at three major columns of data - the LENGTH between bends, ROTATION planes between bends, and BEND ANGLE columns. These columns can be used to define the shape of a tube and setup a tube bender.

The three columns are referred to in many different ways by different bender manufacturers and software developers.

  • "LRA" or "LENGTH, ROTATION, ANGLE" = VTube and Supravision

  • "YBC" = Eaton Leonard Standard Axes, BendPro Controls

  • "PRB" = MiiC

  • "FRB" or FEED, ROTATE, BEND = CNC Bender ProControl for SMT

  • "XYZ" = Pedrazzoli, BLM

  • "FPB" = Chiyoda, KEINS, and COMCO

VTube-LASER Master LRA Data.png


The Limitations of Bender Data for Qualifying Tube Shapes

The tube fabrication industry rarely uses bender data to qualify part shapes because doing that requires the use of angles in the qualification.

There is the major problem with using angles for qualification of tube shapes: Properly qualifying tube shapes with the angules in the bend data is a process that is always dependent on the magnitude of the lengths between bends.

Illustration of the Limitation

Look at the bender data on the right. The two sets are not the same because I've made the MEASURED rotations to be exactly one degree off of the nominal or MASTER data.

Try to answer this question: Given a tolerance envelope of 0.1", does this part qualify or not?

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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