Difference between revisions of "What are Centerline Tangent Points and Why Are They Important in VTube-LASER?"
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* For example, with larger bend angles, the intersection points can be much further from the tube wall. As they move further away from the tube wall, the intersection point deviation grows. This is the nature of polar geometry. One degree of change at 10 mm is 0.17 mm. One degree of change at 1000 mm is 17.45 mm. Tangent points don't have this problem, because they are always closely connected to the straight sections of the tube shape. | * For example, with larger bend angles, the intersection points can be much further from the tube wall. As they move further away from the tube wall, the intersection point deviation grows. This is the nature of polar geometry. One degree of change at 10 mm is 0.17 mm. One degree of change at 1000 mm is 17.45 mm. Tangent points don't have this problem, because they are always closely connected to the straight sections of the tube shape. | ||
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</td> | </td> | ||
</tr> | </tr> | ||
+ | |||
+ | <tr> | ||
+ | <td> | ||
+ | ===A Visual Example of the Problem With Using Intersection Points for Qualification=== | ||
+ | See these two images to help understand the problem with using intersection points for qualification.<br><br> | ||
+ | The white tube is the MASTER part. The pink tube is the MEASURED ALIGNED part. The blue envelopes are the tolerance envelopes for this tube qualification.<br><br> | ||
+ | The two tangents show 0.054 and 0.046 inches in deviation. It's easy to see that the pink straights are well inside the blue envelopes. This part qualifies according to the tangent point deviations. | ||
+ | </td> | ||
+ | <td> | ||
+ | [[image:sharp_angle_solid_3.png|500px]] | ||
+ | </td> | ||
+ | </tr> | ||
+ | |||
+ | <tr> | ||
+ | <td> | ||
+ | However, the intersection points are separated by 0.332 inches.<br><br> | ||
+ | The intersection deviation is <b>6 times larger</b> than the profile deviation of the tube. Intersection deviations do not act as a good representative of the actual profile deviation. It is possible to overqualify a part using them.<br><br> | ||
+ | <br><br> | ||
+ | See [[VTube Intersection Point Tolerances]] for more information about intersection deviations. | ||
+ | </td> | ||
+ | <td> | ||
+ | [[image:sharp_angle_transparent_3.png|500px]] | ||
+ | </td> | ||
+ | </tr> | ||
+ | |||
</table> | </table> | ||
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</table> | </table> | ||
− | =GD&T | + | =GD&T and VTube-LASER Tolerance Envelopes= |
<table cellpadding=10> | <table cellpadding=10> | ||
<tr valign=top> | <tr valign=top> | ||
<td width=800> | <td width=800> | ||
− | + | GD&T tube profile tolerances are always double the VTube-LASER envelope tolerances. So, a GD&T profile tolerance of 3 mm is VTube-LASER's 1.5 mm envelope tolerance. All tolerances that we show below are <b>half</b> the GD&T profile tolerances. | |
</td> | </td> | ||
</tr> | </tr> | ||
+ | |||
+ | <tr valign=top> | ||
+ | <td width=800> | ||
+ | See this end profile image to visualize why GD&T profiles are double the VTube-LASER tolerance envelope. | ||
+ | </td> | ||
+ | <td width=800> | ||
+ | [[image:endprofile_gdt_image.png|500px]] | ||
+ | </td> | ||
+ | </tr> | ||
+ | |||
+ | <tr valign=top> | ||
+ | <td width=800> | ||
+ | This image shows a tube with a 0.060" diameter with a 0.030" envelope in order to visualize the scale of the envelope in VTube. | ||
+ | </td> | ||
+ | <td width=800> | ||
+ | [[image:vtube_scaled_tube_envelope.png|600px]] | ||
+ | </td> | ||
+ | </tr> | ||
+ | |||
+ | |||
</table> | </table> | ||
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− | <td bgcolor=#9999CC width= | + | <td bgcolor=#9999CC width=400> |
This is an actual example from a real print that was shared with us from a Fortune 500 company. This method of specifying tube shape tolerances is becoming the standard in every industry.<br><br> | This is an actual example from a real print that was shared with us from a Fortune 500 company. This method of specifying tube shape tolerances is becoming the standard in every industry.<br><br> | ||
The call-out in the green circle shows GD&T symbols that indicate a datum and tolerances using a feature control frame (the boxes with information). The GD&T tolerance of 6 mm becomes a VTube-LASER envelope tolerance is 3 mm in space for the center legs of the tube.<br><br> | The call-out in the green circle shows GD&T symbols that indicate a datum and tolerances using a feature control frame (the boxes with information). The GD&T tolerance of 6 mm becomes a VTube-LASER envelope tolerance is 3 mm in space for the center legs of the tube.<br><br> | ||
− | The GD&T tolerances at the end in the red circle show a profile tolerance of 3 mm and a perpendicularity tolerance of 2 mm. | + | The GD&T tolerances at the end in the red circle show a profile tolerance of 3 mm and a perpendicularity tolerance of 2 mm for the end component. These are not referring to tube shape - but to the end component's shape and position relative to the tube. See the comments below about the end component. |
− | + | ||
</td> | </td> | ||
− | <td bgcolor=#CCCCFF width= | + | <td bgcolor=#CCCCFF width=600> |
[[image:gd&t_single_view.png|700px]] | [[image:gd&t_single_view.png|700px]] | ||
</td> | </td> | ||
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<td> | <td> | ||
− | Read the GD&T feature control frame for | + | Read the GD&T feature control frame for the tube shape like this:<br><br> |
* Each straight is considered a "Datum A" because the call-out says "9 X the OD of 9.53.<br><br> | * Each straight is considered a "Datum A" because the call-out says "9 X the OD of 9.53.<br><br> | ||
* The circular symbol that looks like a target indicates "true position." True position means that the tolerance is interpreted as a 3D position and not to be locked to an X, Y, or Z axis.<br><br> | * The circular symbol that looks like a target indicates "true position." True position means that the tolerance is interpreted as a 3D position and not to be locked to an X, Y, or Z axis.<br><br> | ||
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</td> | </td> | ||
<td> | <td> | ||
− | [[image:gd&t_single_view_magnified.png| | + | [[image:gd&t_single_view_magnified.png|500px]] |
</td> | </td> | ||
</tr> | </tr> | ||
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− | Read the GD&T feature control frame at the end of the tube like this:<br><br> | + | Read the GD&T feature control frame at the end component of the tube is understood like this:<br><br> |
− | * | + | * The half-circle indicates a profile tolerance. The inside of the end component must conform to the profile of the end of the tube's diameter (9.53) because the datum is "A" - which is the tube diameter. |
− | * The | + | * The tolerance for the end profile is 3 mm. |
− | * The tolerance | + | * This is a maximum material condition - which means that the ID of the end component cannot exceed more than 3 mm outside of the 9.53 diameter. In VTube-LASER terms, the ID of the fitting is constrained to 1.5 mm of tolerance. |
− | * | + | * It would be best to measure the ID with calipers and confirm that it does not exceed an ID of 1.5 mm away from the diameter of the in any direction.<br><br> |
+ | * The next feature control frame shows an upside-down T. It indicates a perpendicularity tolerance of the face of the end component. | ||
+ | * This tolerance cannot exceed a total of 2 mm from perpendicularity from datum B. | ||
+ | * So, the component face may not wobble more than 2 mm from the axis formed between points 1 to 2 - because the circle with an M indicates that this is MAXIMUM MATERIAL CONDITION. This means that the fitting face cannot twist, relative to the tube, more than that tolerance in space. | ||
+ | * To find the exact equivalent in VTube-LASER, it would be best to use a machined adapter with a 90-degree bend attached to the end component. Then set the tangent tolerance for that adapter's centerline at 1 mm - because VTube-LASER deviations are considered spherical radius true positions. | ||
</td> | </td> | ||
<td> | <td> | ||
− | [[image:gd&t_single_view_magnified_end.png| | + | [[image:gd&t_single_view_magnified_end.png|500px]] |
</td> | </td> | ||
</tr> | </tr> |
Latest revision as of 17:16, 18 January 2022
Why are Tangent Points Important in Qualifying Tube Shapes?
Centerline tangent point deviations are important because they represent the best set of points along the centerline to qualify the shape of a tube. |
COMPARE XYZ Tangent Point Deviations to XYZ Intersection Point DeviationsCenterline XYZ intersection points (not the same as centerline XYZ tangent points) are sometimes used for tube shape qualification. However, intersection points are not a good choice for tube-shape qualification because:
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A Visual Example of the Problem With Using Intersection Points for QualificationSee these two images to help understand the problem with using intersection points for qualification. |
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However, the intersection points are separated by 0.332 inches. |
Tangent Point Deviations in the Inspection Data Grid
The Tangent chart is represented by a grid of straights for each row with tangent points and midpoints for each straight:
Note that the two end points are also included in the tangent charts are reports (T1d in straight 1, and T2d in the last straight). They are an exception to the technical tangent definition given above because there is no bend attached to these points. But these points still have value in determining if the part is the correct shape, so it is convenient to include them in this chart and grid - even though they are not really tangents. Midpoint deviations are always less than the highest corresponding tangent deviation, and higher than the lowest corresponding tangent deviation. They are included in traditional reports so that you can have three separate deviation tolerances in a straight. (T1-MP-T2)
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The Same Data In Reports
The same tangent data can be shown in the reports like this. |
How to Understand the Tangent Data
About End Point Deviations
Automatic Internal Trimming of End Points for Shape
Even though the end points are not tangents, we can still use them in the chart because they qualify the part the same way that tangent points do. |
Untrimmed End Points for Lengths
However, the end length is 90.2mm too long. In this application, the customer bent the part 90mm too long on purpose in order to give the bend arm clamp die enough material on the first straight to grip. Notice that, even though the part is significantly too long, the BEST FIT algorithm didn't use the actual measured end point in the alignment. The alignment was based on the trimmed point on the measured centerline that was nearest the master end point. So, in this case the part shape in space is qualified - but it needs trimming by 90.2mm to also qualify the end length (another critical qualifier). |
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)
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GD&T and VTube-LASER Tolerance Envelopes
GD&T tube profile tolerances are always double the VTube-LASER envelope tolerances. So, a GD&T profile tolerance of 3 mm is VTube-LASER's 1.5 mm envelope tolerance. All tolerances that we show below are half the GD&T profile tolerances. |
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See this end profile image to visualize why GD&T profiles are double the VTube-LASER tolerance envelope. |
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This image shows a tube with a 0.060" diameter with a 0.030" envelope in order to visualize the scale of the envelope in VTube. |
GD&T Feature Control Frame Examples
This is an actual example from a real print that was shared with us from a Fortune 500 company. This method of specifying tube shape tolerances is becoming the standard in every industry. |
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Read the GD&T feature control frame for the tube shape like this:
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Read the GD&T feature control frame at the end component of the tube is understood like this:
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Other Pages
- About VTube-LASER End Point Deviations
- What are Centerline Tangent Points and Why Are They Important in VTube-LASER?
- About VTube Intersection Point Tolerances
- About VTube End Length Offsets
- Back to VTube-LASER