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Auto plane vs Constructed plane





Hello. I'm trying to inspecthe true position of the 3.16mm hole per drawing requirement. I leveled the cyl B to Zplus and rotated the mid plane of datum A to X. Z0 is the plane at the end of culinder B, X0 is the midplane A and Y0 is the Axis of Cylinder B. After the alignment, i measured the datum C plane using Auto plane(6 points spread out) by picking it off the CAD with the A=90B0 probe angle. And 3.16mm hole is measured as a cylinder(4 levels, 5 hits per level, probe angle A90B90). When i build the FCF per drawing and output the result, i'm getting a result thats really out(about 2.2). All the basic dimensions listed on the drawing are close to nominal(7.7 is 7.706, 18.36 is 18.41, the angle 55 is 55.005) and the angulatity is like 0.011).

But when i meaure 6 vector points (again using A90B0 probe angle) and used those points to construct a plane(best fit, least sq) and assign that as datum C, my results are way better and close to what the supplier has listed(0.097).

And whe i changed my hit targets on the auto plane to differnt spots on the plane, i get a different reading but still out of tol. Why is the program giving a different result when a auto plane is used as a datum vs a constructed plane is used as the same datum? what could cause this issue? Any help or advise/tip is really appriciated.

Thank you in advance.

i'm using 2019R2 version
Parents
  • {"alt":"Click image for larger version Name:\tplane C_auto.jpg Views:\t52 Size:\t47.8 KB ID:\t537512","data-align":"none","data-attachmentid":"537512","data-size":"full","title":"plane C_auto.jpg"} {"alt":"Click image for larger version Name:\tvector points.jpg Views:\t50 Size:\t66.9 KB ID:\t537514","data-align":"none","data-attachmentid":"537514","data-size":"full","title":"vector points.jpg"}{"alt":"Click image for larger version Name:\tplane C_constuction.jpg Views:\t50 Size:\t14.1 KB ID:\t537513","data-align":"none","data-attachmentid":"537513","data-size":"full","title":"plane C_constuction.jpg"}

    @ Rider: Here are the codes ​​for teh auto plane, vector ponts and the constructed plane. Void detection is not activated when the Auto plane was done.
    @Jefman: both the flatnesses are similar(.002, 0.003) and the angularities are similar as well.

    Really need some help as this is puzzling me a lot.

    Thank you Slight smile




    Firstly, your auto-plane needs to be re-executed because all of the hit values have been reset to nominal. This can happen if you edit the auto-feature after measuring because any change in the dialog (even just opening it and clicking "create" instead of "cancel" will cause the hits to be reset).
    Second, you have less hits for your constructed plane (4 hits) than for your auto-plane (6 hits) and they are in different locations.
    Third, you should be using BFRE for the constructed plane rather than BF.

    If (as others have already suggested) you measure 6 vector points at exactly the same locations as the auto-plane hits and then construct a least squares BFRE plane from them, they should yield exactly the same result as the auto-plane when used in a Geometric Tolerance command with least squared datum math selected.
Reply
  • {"alt":"Click image for larger version Name:\tplane C_auto.jpg Views:\t52 Size:\t47.8 KB ID:\t537512","data-align":"none","data-attachmentid":"537512","data-size":"full","title":"plane C_auto.jpg"} {"alt":"Click image for larger version Name:\tvector points.jpg Views:\t50 Size:\t66.9 KB ID:\t537514","data-align":"none","data-attachmentid":"537514","data-size":"full","title":"vector points.jpg"}{"alt":"Click image for larger version Name:\tplane C_constuction.jpg Views:\t50 Size:\t14.1 KB ID:\t537513","data-align":"none","data-attachmentid":"537513","data-size":"full","title":"plane C_constuction.jpg"}

    @ Rider: Here are the codes ​​for teh auto plane, vector ponts and the constructed plane. Void detection is not activated when the Auto plane was done.
    @Jefman: both the flatnesses are similar(.002, 0.003) and the angularities are similar as well.

    Really need some help as this is puzzling me a lot.

    Thank you Slight smile




    Firstly, your auto-plane needs to be re-executed because all of the hit values have been reset to nominal. This can happen if you edit the auto-feature after measuring because any change in the dialog (even just opening it and clicking "create" instead of "cancel" will cause the hits to be reset).
    Second, you have less hits for your constructed plane (4 hits) than for your auto-plane (6 hits) and they are in different locations.
    Third, you should be using BFRE for the constructed plane rather than BF.

    If (as others have already suggested) you measure 6 vector points at exactly the same locations as the auto-plane hits and then construct a least squares BFRE plane from them, they should yield exactly the same result as the auto-plane when used in a Geometric Tolerance command with least squared datum math selected.
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