What are Centerline Tangent Points and Why Are They Important in VTube-LASER?
Reading the T1d, MP, T2d Chart
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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:
Technically a tangent point is the point where any straight meets any bend. These are considered the best points for qualifying a tube shape because the are the points that most closely approximate the walls of a tube gauge. The two end points are an exception to the technical tangent definition given above. There is no bend attached to these points. But these points (T1d in straight 1, and T2d in the last straight) 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. The general rule is this: If the tangent points are within tolerance, then it follows that the shape of the part - based on the straights - fits well enough inside the tolerance envelope in order to qualify. In GD&T, this is often referred to as the centerline profile. |
How to Understand the Chart
How to Read the End Point Deviations
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. The end is 90.2mm too long (see the length portion of the inspection grid above), but the measured first straight passes within 1.9mm of the master end point. So the T1d value is 1.9mm - not 90.2mm. In this application, the customer bent the part 90mm too long on purpose in order to give the clamp 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 point along 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). |
Set the Default
Set the default value by clearing the VTube project, then changing the value, then saving the setup to the default file in the System Options - Project Setup menu. |
Other Pages
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