Difference between revisions of "The Limitations of Qualifying Tube Shapes using Bender Data"
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The tube fabrication industry is rapidly abandoning the use of bender data deviations to qualify part shapes for a very good reason.<br><br> | The tube fabrication industry is rapidly abandoning the use of bender data deviations to qualify part shapes for a very good reason.<br><br> | ||
The problem with using bender data deviations for the qualification of a part shape is that it does not help you know if a part is inside or outside of 3D envelopes (or GD&T profiles) for each straight section in a tube shape without additional polar to linear calculations. Spatial envelopes represent the specific path in 3D space where the tube must be inside of in order to not cause a collision or rub itself to failure from vibration.<br><br> | The problem with using bender data deviations for the qualification of a part shape is that it does not help you know if a part is inside or outside of 3D envelopes (or GD&T profiles) for each straight section in a tube shape without additional polar to linear calculations. Spatial envelopes represent the specific path in 3D space where the tube must be inside of in order to not cause a collision or rub itself to failure from vibration.<br><br> | ||
− | In VTube-LASER, this allowed space is called the ENVELOPE | + | In VTube-LASER, this allowed space is called the ENVELOPE as defined by the TANGENT points along each straight in the defined tube (see the image on the right). (Tangent points are where the straights meet the bends.)<br><br> |
The ENVELOPE always includes a tolerance of deviation allowed. Think of the deviation as a spherical radius true position from the MASTER centerline. | The ENVELOPE always includes a tolerance of deviation allowed. Think of the deviation as a spherical radius true position from the MASTER centerline. | ||
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− | <td> | + | <td width=400> |
[[image:exhaust_envelope_tolerance.png|400px]]<br> | [[image:exhaust_envelope_tolerance.png|400px]]<br> | ||
+ | The above image is an example of an exhaust pipe with a blue band around the straight section. This blue band is the envelope tolerance.<br> | ||
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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.<br><br> | 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.<br><br> | ||
Try to answer this question: ''Given a tangent point envelope tolerance envelope of 0.100"'', does this part qualify or not?<br><br> | Try to answer this question: ''Given a tangent point envelope tolerance envelope of 0.100"'', does this part qualify or not?<br><br> | ||
+ | This is the problem: There is no way to guess if this part is actually inside its allowed envelope in 3D space without performing some moderately complex trig calculations. | ||
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− | + | So, unless you can perform 3D trigonometry 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.<br><br> | |
It's easy to visually demonstrate the limitation of using bender data to tell us if a part shape falls within the tolerance envelope.<br><br> | It's easy to visually demonstrate the limitation of using bender data to tell us if a part shape falls within the tolerance envelope.<br><br> | ||
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− | + | The illustrations above show that the best data for tube shape qualification inside an envelope is centerline TANGENT POINT data in the Inspection Data menu and in the Reports menu.<br><br> | |
[[image:vtube-laser-t1d-mp-t2d-image1.png|500px]]<br><br> | [[image:vtube-laser-t1d-mp-t2d-image1.png|500px]]<br><br> | ||
For more information, see [[What are Centerline Tangent Points and Why Are They Important in VTube-LASER?]] | For more information, see [[What are Centerline Tangent Points and Why Are They Important in VTube-LASER?]] | ||
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=Typical Industry Tangent Point Envelope Tolerances= | =Typical Industry Tangent Point Envelope Tolerances= |
Latest revision as of 19:58, 24 January 2020
This page explains the major limitations of using bender data for qualifying tube shapes.
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Contents |
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.
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ENVELOPES Qualifying Tube Shapes Are Much Better Than Bender Data Deviations Qualifying Tubes
Illustration of the LimitationLook 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. |
Visually Demonstrate the Problem of Qualifying with Angles
So, unless you can perform 3D trigonometry 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. |
INSIDE THE ENVELOPES: QUALIFIES |
OUTSIDE THE ENVELOPES: DOES NOT QUALIFY |
Example 2
We show another smaller part with two tolerance envelope setups. |
The Best Data for Qualification
The illustrations above show that the best data for tube shape qualification inside an envelope is centerline TANGENT POINT data in the Inspection Data menu and in the Reports menu. |
Typical Industry Tangent Point Envelope 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
Automotive Exhaust Pipes
Automotive Fluid Lines
Shipbuilding
HVAC
Structural Tubes (Frames)
Tighter TolerancesSometimes customers will require +/-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. |