Difference between revisions of "VTube-LASER Cylinder Fit Tolerances"

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(How to Test for Your Ideal Tolerances)
(How to Test for and Use Cylinder Fit Tolerances for Your Application)
 
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[[image:vtube-laser_logo_1.96.png|300px]]<br><br><br>
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How Does VTube-LASER Use Cylinder Fit Tolerances?
* Back to [http://www.advancedtubular.com/vtube-laser.htm the Main VTube-LASER] web page
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 +
 
 
* Back to [[VTube-LASER]]
 
* Back to [[VTube-LASER]]
 
* Back to [[VTube-STEP]]
 
* Back to [[VTube-STEP]]
 
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[[image:vtube-laser_1.89_mainscreen.png|300px]]<br>
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[[image:vtube-laser_logo_1.96.png|200px]]<br><br><br>
 
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__NOTOC__
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__TOC__
  
="How Well Does Centerline Fit the Cylinder Surface Points?"=
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=Answer=
 
<table>
 
<table>
 
<tr>
 
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<td width=400>
 
<td width=400>
VTube-LASER uses surface points scanned with laser or measured with ball probes to calculate tube centerlines.<br><br>
+
VTube-LASER uses scanned surface points to calculate tube centerlines.<br><br>
Regular tube scans assume that the primitive shape to solve for is a cylinder.<br><br>
+
Regular tube scans assume that the primitive shape to solve for is a cylinder. But we also assume that no cylinder that we measure in the real world is a '''perfect''' cylinder.<br><br>
When solving for a cylinder centerline, it's important for you to know the estimated accuracy of the calculation. The estimated accuracy helps you know how confident you can be with the centerline position.<br><br>
+
VTube-LASER has to overcome this issue when measuring tube straights.<br><br>
 +
Also, because of this, it's important for you to know the estimated accuracy of the calculation when fitting to the centerline. The estimated accuracy helps you know how confident you can be with the centerline position.<br><br>
 
</td>
 
</td>
 
<td>
 
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After calculating a cylinder centerline from surface points, VTube-LASER reports how well the centerline FITS the surface points of the cylinder. These values are shown in the Cylinder Fit Data window.<br><br>
 
After calculating a cylinder centerline from surface points, VTube-LASER reports how well the centerline FITS the surface points of the cylinder. These values are shown in the Cylinder Fit Data window.<br><br>
 
The values reported are...<br><br>
 
The values reported are...<br><br>
* RADIUS: Estimate the maximum deviation of half the diameter.<br><br>
+
* RADIUS: Estimate the precision of half the diameter.<br><br>
* X or Y POSITION: Estimate the deviation of the X or Y positions of the end points of the cylinder.<br><br>
+
* X or Y POSITION: Estimate the precision the X or Y positions of the end points of the cylinder.<br><br>
These estimate values are calculated using statistical math. The values are standard deviation x 2, which means that we have 95% assurance that the these values are the maximum deviation.
+
These estimate values are calculated using statistics. The values are standard deviation x 2, which means that it gives a 95% assurance that the these values are the precision of the positions.<br>
 +
[[image:Vtube-laser_cylinderfitwindow2.jpg|300px]]<br>
 
</td>
 
</td>
 
<td width=350 VALIGN="top">
 
<td width=350 VALIGN="top">
[[image:Vtube-laser_cylinderfitwindow.jpg|300px]]<br>
+
[[image:cylindricity graphic.png|500px]]<br><br>
 +
[[image:wobble illustration.png|500px]]<br>
 
</td>
 
</td>
 
</tr>
 
</tr>
 
</table>
 
</table>
  
=Wobble Deviation - The highest of the X or Y values=
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=Cylinder Wobble - The highest of the X or Y values=
 
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To simplify visualizing the X and Y Position deviation, we say that the '''highest of the X and Y values is the "wobble deviation"'''. The wobble deviation in the example on the right is 0.21 inches - because it is the higher of the two values.<br><br>
+
To simplify visualizing the X and Y positions, we say that the '''highest of the X and Y values is the "cylinder wobble"'''. The cylinder wobble in the example on the right is 1.3036 inches - because it is the higher of the two values.<br><br>
 
If the centerline calculation is very good, then wobble deviation decreases. If the calculation or fit is poor, then the wobble deviation is too high.<br><br>
 
If the centerline calculation is very good, then wobble deviation decreases. If the calculation or fit is poor, then the wobble deviation is too high.<br><br>
This Cylinder Fit Data window is YELLOW because VTube-LASER found that the X and Y Position tolerances were exceeded in the cylinder centerline fit. In this case, VTube asked the operator to remeasure the straight because the wobble deviation was too high as defined by the tolerances in System Options/Measure 1.
+
This Cylinder Fit Data window is Red because VTube-LASER found that the X and Y Position tolerances were exceeded in the cylinder centerline fit. In this case, VTube asked the operator to remeasure the straight because the cylinder wobble was too high as defined by the tolerances in System Options/Measure 1.
 
<br> <br>
 
<br> <br>
 
</td>
 
</td>
 
<td width=350>
 
<td width=350>
[[image:vtube-laser_wobbledeviation.png|300px|right]]
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[[image:vtube-laser_wobbledeviation2.png|300px|right]]
 
</td>
 
</td>
 
</tr>
 
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</table>
 
</table>
  
==Default Cylinder Fit Tolerances==
+
=Controlling Cylinder Fit Tolerance Values=
 +
VTube-LASER uses tolerance values to decide when to warn you about potentially poor cylinder measurements.<br><br>
 +
These values can be adjusted in the Measure 1 menu of System Options.
 +
 
 +
 
 +
==Default Tolerances==
  
  
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To allow VTube-LASER to warn for poor cylinder measurements, it stores tolerances for the allowed deviations during cylinder fit. These values are often setup in the Measure 1 tab of the System Options menu.<br><br>
+
The default values are designed as a good starting point in the VTube-LASER setup. They are excellent for quick demonstrations of the software, and work great for tubes that have a lot of deformation in the straights.<br><br>
The default values are shown in the screen image on the right.<br><br>
+
Large-diameter applications (like exhaust pipes) are good candidates for this setup.<br><br>
For less precise diameters like exhaust pipes, these settings usually work well. If you measure highly oval or deformed parts, it may be necessary to increase especially the X and Y Position tolerances.
+
 
</td>
 
</td>
 
<td width=500>
 
<td width=500>
[[image:vtube-laser_default_CylinderFitTolerances.png|500px|right]]
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[[image:vtube-laser_default_CylinderFitTolerances2.png|500px|right]]
 
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</table>
  
 
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==Aerospace Tolerances==
==Recommended Aerospace Cylinder Fit Tolerances==
+
  
  
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Aerospace-grade materials are often very precise. For aerospace applications, we strongly recommend that you consider using tighter tolerances like these shown here.<br><br>
+
Aerospace-grade materials are more precise compared to other applications. For aerospace applications, we recommend that you use tighter tolerances like the ones shown here.<br><br>
The XY Positions should be 0.030" for longer straights, and 0.050" for shorter straights. ("Short" is also definable with the variable in the lower right corner.  It is set to 2" length by default.)
+
The XY Positions are set to 0.030" for longer straights, and 0.050" for shorter straights. ("Short" is also definable with the variable in the lower right corner.  It is set to 2" length by default.)
 
</td>
 
</td>
 
<td width=500>
 
<td width=500>
[[image:vtube-laser_default_CylinderFitTolerances aerospace.png|500px|right]]
+
[[image:vtube-laser_default_CylinderFitTolerances aerospace1.png|500px|right]]
 
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</table>
 
</table>
  
==How to Test for Your Ideal Tolerances==
+
==How to Test for and Use Cylinder Fit Tolerances for Your Application==
  
  
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<td width=400>
 
<td width=400>
You can test for ideal cylinder fit tolerance settings by watching the tolerance values in the Cylinder Fit window when measuring a tube.<br><br>You will learn that your material regularly measures with maximum fit deviation. You can adjust the tolerances in System Option to better fit your application and increase the assurance that your centerline is a good fit to the surface data.<br><br>
+
You can adjust the tolerances in System Options to better fit your application and increase the assurance that your centerline is a good fit to the surface data.<br><br>
 +
 
 +
Test for ideal cylinder fit tolerance settings by measuring tubes and watching the tolerance values in the Cylinder Fit window.<br><br>You will learn that your material regularly measures with certain maximum fit deviations.<br><br>
 +
 
 +
As an example, if you never see deviations over 0.0159" (like shown on the right), you could set the tolerance value to 0.040" (which is just over double the max observed). If a cylinder fit deviation exceeds double the norm, then you can safely assume that there is a problem in the measurement, and you should be warned.<br><br>
 +
 
 +
When watching for these values during measurements, keep in mind that you need to consider both the longer straight and shorter straight tolerances.  Short straights will nearly always need higher tolerances.
 +
 
 
To change the default values, be sure to CLEAR the VTube-LASER project first, then press the "Set Project Default State to the current state" button. This will use the new default cylinder fit tolerances for all new projects.</td>
 
To change the default values, be sure to CLEAR the VTube-LASER project first, then press the "Set Project Default State to the current state" button. This will use the new default cylinder fit tolerances for all new projects.</td>
 
<td width=500>
 
<td width=500>
[[image:vtube set default project state to the current state.png|400px]]
+
[[image:Vtube-laser_cylinderfitwindow3.jpg|300px]]<br><br>
 +
[[image:vtube set default project state to the current state1.png|400px]]
 
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</table>
 
</table>
  
==Other Pages==
+
=Why Are There Separate Values for Shorter Straights?=
 +
 
 +
 
 +
<table cellpadding=10>
 +
<tr valign=top>
 +
<td width=300>
 +
Math engines cannot calculate short straights as accurately as long straights. This has to do with the nature of cylinder math. It's a common issue with all measuring centers. Because of this, we know that VTube needs to be more patient with when fitting a cylinder centerline when the straight length is below a certain value.<br><br>
 +
In the default setup for VTube-LASER, a straight is considered "short" when it is 2 inches (50.8 millimeters) or shorter.
 +
</td>
 +
<td width=500>
 +
[[image:vtube-laser_default_CylinderFitTolerances short straight value.png|500px|right]]
 +
</td>
 +
</tr>
 +
 
 +
</table>
 +
 
 +
=Other Pages=
 
* Back to [[VTube-LASER]]
 
* Back to [[VTube-LASER]]
* Back to [[VTube-STEP]]
+
* See also [[Why VTube-LASER Reduces Data to Centerlines]]
 +
* See also [[VTube-LASER Prioritizes Measuring Tube Straights]]

Latest revision as of 13:55, 24 June 2022

How Does VTube-LASER Use Cylinder Fit Tolerances?


Vtube-laser logo 1.96.png



Contents


Answer

VTube-LASER uses scanned surface points to calculate tube centerlines.

Regular tube scans assume that the primitive shape to solve for is a cylinder. But we also assume that no cylinder that we measure in the real world is a perfect cylinder.

VTube-LASER has to overcome this issue when measuring tube straights.

Also, because of this, it's important for you to know the estimated accuracy of the calculation when fitting to the centerline. The estimated accuracy helps you know how confident you can be with the centerline position.

Vtube-laser cylinder surfacepoints.png

The Cylinder Fit Data Window Reports How Well the Centerline Fits the Surface Data

After calculating a cylinder centerline from surface points, VTube-LASER reports how well the centerline FITS the surface points of the cylinder. These values are shown in the Cylinder Fit Data window.

The values reported are...

  • RADIUS: Estimate the precision of half the diameter.

  • X or Y POSITION: Estimate the precision the X or Y positions of the end points of the cylinder.

These estimate values are calculated using statistics. The values are standard deviation x 2, which means that it gives a 95% assurance that the these values are the precision of the positions.
Vtube-laser cylinderfitwindow2.jpg

Cylindricity graphic.png

Wobble illustration.png

Cylinder Wobble - The highest of the X or Y values

To simplify visualizing the X and Y positions, we say that the highest of the X and Y values is the "cylinder wobble". The cylinder wobble in the example on the right is 1.3036 inches - because it is the higher of the two values.

If the centerline calculation is very good, then wobble deviation decreases. If the calculation or fit is poor, then the wobble deviation is too high.

This Cylinder Fit Data window is Red because VTube-LASER found that the X and Y Position tolerances were exceeded in the cylinder centerline fit. In this case, VTube asked the operator to remeasure the straight because the cylinder wobble was too high as defined by the tolerances in System Options/Measure 1.

Vtube-laser wobbledeviation2.png

Controlling Cylinder Fit Tolerance Values

VTube-LASER uses tolerance values to decide when to warn you about potentially poor cylinder measurements.

These values can be adjusted in the Measure 1 menu of System Options.


Default Tolerances

The default values are designed as a good starting point in the VTube-LASER setup. They are excellent for quick demonstrations of the software, and work great for tubes that have a lot of deformation in the straights.

Large-diameter applications (like exhaust pipes) are good candidates for this setup.

Vtube-laser default CylinderFitTolerances2.png

Aerospace Tolerances

Aerospace-grade materials are more precise compared to other applications. For aerospace applications, we recommend that you use tighter tolerances like the ones shown here.

The XY Positions are set to 0.030" for longer straights, and 0.050" for shorter straights. ("Short" is also definable with the variable in the lower right corner. It is set to 2" length by default.)

Vtube-laser default CylinderFitTolerances aerospace1.png

How to Test for and Use Cylinder Fit Tolerances for Your Application

You can adjust the tolerances in System Options to better fit your application and increase the assurance that your centerline is a good fit to the surface data.

Test for ideal cylinder fit tolerance settings by measuring tubes and watching the tolerance values in the Cylinder Fit window.

You will learn that your material regularly measures with certain maximum fit deviations.

As an example, if you never see deviations over 0.0159" (like shown on the right), you could set the tolerance value to 0.040" (which is just over double the max observed). If a cylinder fit deviation exceeds double the norm, then you can safely assume that there is a problem in the measurement, and you should be warned.

When watching for these values during measurements, keep in mind that you need to consider both the longer straight and shorter straight tolerances. Short straights will nearly always need higher tolerances.

To change the default values, be sure to CLEAR the VTube-LASER project first, then press the "Set Project Default State to the current state" button. This will use the new default cylinder fit tolerances for all new projects.

Vtube-laser cylinderfitwindow3.jpg

Vtube set default project state to the current state1.png

Why Are There Separate Values for Shorter Straights?

Math engines cannot calculate short straights as accurately as long straights. This has to do with the nature of cylinder math. It's a common issue with all measuring centers. Because of this, we know that VTube needs to be more patient with when fitting a cylinder centerline when the straight length is below a certain value.

In the default setup for VTube-LASER, a straight is considered "short" when it is 2 inches (50.8 millimeters) or shorter.

Vtube-laser default CylinderFitTolerances short straight value.png

Other Pages