Form vs Profile vs Cloud 2 CAD

Setup

A planar surface was created in CAD, normal to the Z axis, with an X width of 50mm and a Y length of 100mm.  This is used as the Nominal surface in all cases.  6 points were "measured" and the same 6 points were used for all examples.  The point numbers and locations are included for reference.

Two alignments are used for the example reports.

1. Normal to the Nominal surface
   
2. Normal to the Actual surface

Examples are 2D "Edge View" to better show the error calculation.

3D View

Note that the Nominal plane is 50mm x 100 as defined.  The Actual plane is 39.4769mm x 79.5163mm as bounded by the actual points, and is tilted around both X and Y as well as a slight rotation around Z compared to the nominal.

Top view

For all cases below -

If measured as a feature, Compensation should be On.

If measured as individual points and constructing the feature later, or doing Cloud 2 CAD, the Compensation should always be Off to avoid cosine compensation error where the points/cloud were compensated normal to the nominal feature instead of correctly compensated along the normal of the actual feature.

Form

Form is calculated as the difference between the highest and lowest point normal to the actual feature.  I this case, point #2 was at +0.9872mm and point #5 was at -0.7407mm.  The difference is 1.7279mm which is the reported value for form.

Since Form is always relative to the actual feature, and independent of the current reference frame, the report of Form will always be the same no matter what the current active reference frame is.

Profile

Profile is calculated as 2x the absolute (whether + or -) worst point deviation from the nominal feature.  The range of data was from +6.5790 to -4.7988.  The worst case is +6.5790.  So the report value is 2x the worst case (Per ASME, the total zone used), so 13.1579.  The value is always an absolute (positive) reported value.

Beginning with CMM-Manager 2024, Profile would be the preferred method of reporting Cloud to CAD.  Profile allows the option of using Total Tolerance Zone (ASME - 2x the worst deviation) or, if unchecked, the simple worst deviation will be reported.

Alignment normal to Nominal

Alignment normal to Actual

Cloud to CAD

Cloud to CAD is reported as the worst point deviation from the nearest CAD surface.  The range of data was from +6.5790 to -4.7988.  The worst case is +6.5790.  So the report value is the worst case , so 6.5790.  The value is always an absolute (positive) reported value.  This will be the value reported in the Cloud 2 CAD report in the header section of the report.

If the Profile checkbox is also selected, it will be reported (per ASME) as 2x the worst case deviation as it's own report item.  The value in the Profile report item will not match the value in the Cloud 2 CAD header.  To report Profile as just the worst case, see options in Profile above.

If using any Best Fit options, you must use the points include in the best fit output.  If points which are reported outside the best fit report are used, the values will not corelate.

Alignment normal to CAD surface

Alignment normal to Actual

What went wrong?

Some of the more common reasons that you do not get the expected results are:

1. The feature nominal is incorrect.  If the feature was taught via joystick instead of CAD, it will be necessary to edit the feature nominal to match the print values.
   
2. The correct alignment has not been selected.
   
1. If using the Current Ref. Frame option, make sure the current alignment is the same as the alignment required for the reported item.
   
2. If using New Ref. Frame, verify that the correct features have been selected, and as above, make sure that the ref. frame feature nominals are correct.
   
3. If constructing features from points/cloud or doing Cloud 2 CAD, the points should always be non-compensated.  Otherwise a small of cosine error will be introduced.
4. If using Best Fit / Datum Locks with partial datums, make sure that the locks are unchecked for the items that are not part of the tolerance requirement.
   
5. Other possibilities include incorrectly constructed ref. frames, feature/ref. frame sync issues.

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