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 for a very good reason.

The problem with using bender data for qualification of a part shape is that it does not help you know if a part is inside or outside of the tolerance envelopes for each straight section in a tube shape. Tolerance envelopes indicate specific places in XYZ space where the tube must follow as closely as possible (or at least within tolerance).

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 away from MASTER data rotations.

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 make a guess, we can't 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 aligned parts on the image. The white tube is the MASTER. The pink tube is the MEASURED ALIGNED. 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 as defined by the Tangent Grid. 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

Example 2

We show another smaller part with two tolerance envelope setups.

Both parts are the same shape - and they have some easy-to-see deviation in the bender data. However, one is acceptable, and the other part is not.


The Best Data for Qualification

You've probably already figured out from the examples above that the best data for tube shape qualification is centerline TANGENT POINT 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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