VTube Intersection Point Tolerances

XYZ Intersection Tolerances Back to VTube-LASER

Important Note About the Limitations of Using XYZ Intersection Point Deviations To Qualify a Part Shape

Before describing the intersection point tolerances, it is important to note that XYZ tangent points (not discussed on this page) are the preferred points to use for tube shape qualification. The reason is because intersection points are not as good as tangent points for tube-shape qualification. Here is why:

• Intersection deviations tend to exaggerate the deviations mathematically.
  
  
• The reason why they exaggerate the deviation is because they are not as close to OD wall in the straight as tangent points are.
  
  
• The higher the bend angle at an intersection, the further the intersection points are from the actual part - which means that the deviation exaggeration is greater as the bend angles increase. Tangent points don't have this problem, because they are always closely connected to the straight sections of the tube shape.

See What are Centerline Tangent Points and Why Are They Important in VTube-LASER? for more information about tangent point deviations.

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.

The two tangents show 0.054 and 0.046 inches in deviation. However, the intersection points are separated by 0.322 inches.

The intersection deviation is 6 times larger than the profile deviation of the tube. However, it is easy to see that the part falls well within the envelopes (the transparent blue cylinders) that are formed by the tangent deviations. Intersection deviations do not act as a good representative of the actual profile deviation.

Why Include Intersection Deviations in the VTube Interface?

The only reason we include intersection point deviations in reports because some customers require them for part qualification.

How the XYZ Intersection Deviation Tolerances Work

The XYZ intersection deviation tolerances allow you to quickly qualify a part using +/- tolerances to the intersection points. The intersection tolerances are based on values are that follow the three axes in a coordinate system. Since the tolerances measure along the axes, these tolerances can be positive or negative to also indicate a direction.

XYZ Intersection Deviations

The XYZ intersection deviation tolerances are are compared to the XYZ deviations as shown in the model in this screen image. In this case, most of the error is in the Y axis. It can be verified by seeing that the intersection point of the derived data is visually above the master point. (You can click on the image to make it larger.) The deviation data indicates that it is exactly 0.012" above the master point in the Y axis. The reason the grid is entirely green is because the tolerance values are higher than the deviation values (in this case the tolerances are 0.039"). 3D Deviation The 0.013" value is the straight-line distance measured directly from the master to the corresponding measured points. This is different than the deviation broken down into one of the major axes (X,Y,Z). Unless the 3D deviation line also lays on one of the major axes, it is usually larger than any of the intersection deviation values - because it combines the deviation of all three axes. Most customers do not rely on this distance to qualify the part shape. Like XYZ intersection deviations, these values almost always exaggerate the true deviation to the outside of the straights in the tube.

Set the Default Tolerance in Part Setup Menu

You can set the default tolerance in the Part Setup menu. Scroll down to row 34.

Set the Default Tolerance in General Setup Menu

You can set the default tolerance in the Inspection Data General Setup menu. (This is for version 2.5 and newer.)

Set the Default Tolerance in Inspection Data Menu

You can set the default tolerance in the Inspection Data menu by entering a Default Tolerance at the top and pressing the Set button.

Set the Tolerances in Inspection Data Grids

Click on the Change Grid Setup button until you see the tolerances in the grid like we show in the image on the right. Then select and change any tolerance value. The grid will allow you to edit only the tolerances.

Set the Tolerances in Expanded Windows

The second place to edit the value is in the VTube-LASER Expanded Window. Click on the Expanded Window button to display the Expanded Window, and then make changes to the tolerances there. The benefit of the Expanded Window is that you can view all the tolerances at the same time.

(You can click on the image to see it larger.)

Setting All The Tolerances At The Same Time

The intersection deviation grids allow you to set the default tolerance to every value in a row, column, or even the entire grid using a popup menu To use this feature, single click on a tolerance value, then right click and choose the action in the popup menu.

The screen images on the right show an example of before and after changes made to an entire column:

Before After

XYZ Intersection +/- Tolerance Values in Printed Reports

The XYZ Intersection deviation values can be included in reports: plus tolerance values minus tolerance values out of tolerance values The first Inspection Report in the reports menu is good for showing this data.

Other Pages

• About VTube-LASER End Point Deviations
• What are Centerline Tangent Points and Why Are They Important in VTube-LASER?
• About VTube End Length Offsets
• The Limitations of Qualifying Tube Shapes using Bender Data
• Back to VTube-LASER