It is actually a little bit more than that if you are NOT using SNAP for your vector points or if you are using SURFACE points or EDGE points. If not using SNAP points, the vector values are included in the formula, BUT, the T value will ALWAYS show as if you used SNAP.
If you don't use snap, you COULD see something like this: XNOM 0 XVector 0 YNOM 0 YVector 0 ZNOM 0 ZVector 1 This would be a point, straight up and down. Now, NO MACHINE is perfect, they ALL have some amount of drift, so your touch COULD be this (grossly exaggerated and in METRIC): XACT 0.125 YACT -0.105 ZACT 1.124
No matter SNAP or no, your T deviation in this case will be 1.124, HOWEVER, if you trig it out (as some will do), you would think it would be 1.135, but that would NOT be along the vector of the point SQRT (0.125^2 + -0.105^2 + 1.124^2) = 1.135 When done using the vectors, well, ZERO times anything is zero, so: SQRT ( (0.125*0)^2 + (-0.105*0)^2 + (1.124*1)^2) ) = 1.124 the 1.124 is what the T value will ALWAYS be in this example, BUT, by using SNAP (which put the actual reading back on the perfect vector line), it removes the drift from all 3 axis. Now, some will say this hides a sloppy machine, and yes, it can, BUT, this example is a VERY exaggerated example of how much drift you might see. On my old (OLD! 20+ years old) machine, I get less than 0.002" of drift and that really won't show up unless you are trying to hold micron values.
I was explained in PCDMIS CAD++ class that snap point is to correct machine drift mathematically not hiding machine drift (at least that the impression that I got). Example:Blue print defined a point on a complex surface at XY exact position (basic dimensions) and the third axis (Z) must meet blue print requirement at that position. The snap point does just that by re-calculating the actual Z value at exact position (theoretical position).
I remembered the instructor said he was helping one of his customers measuring a complex curve surface using CAD and the DCC of the machine is very sloppy, the part they were checking is a known good part but the result proved otherwise he then suggested to use snap point and everything fall in.
Your explanation is exactly the same as stated in PCDMIS help file.
I have read many of your postings and I know you are among the very best in the country, I have no doubt of your assessment. I am just confused!!!
It is actually a little bit more than that if you are NOT using SNAP for your vector points or if you are using SURFACE points or EDGE points. If not using SNAP points, the vector values are included in the formula, BUT, the T value will ALWAYS show as if you used SNAP.
If you don't use snap, you COULD see something like this: XNOM 0 XVector 0 YNOM 0 YVector 0 ZNOM 0 ZVector 1 This would be a point, straight up and down. Now, NO MACHINE is perfect, they ALL have some amount of drift, so your touch COULD be this (grossly exaggerated and in METRIC): XACT 0.125 YACT -0.105 ZACT 1.124
No matter SNAP or no, your T deviation in this case will be 1.124, HOWEVER, if you trig it out (as some will do), you would think it would be 1.135, but that would NOT be along the vector of the point SQRT (0.125^2 + -0.105^2 + 1.124^2) = 1.135 When done using the vectors, well, ZERO times anything is zero, so: SQRT ( (0.125*0)^2 + (-0.105*0)^2 + (1.124*1)^2) ) = 1.124 the 1.124 is what the T value will ALWAYS be in this example, BUT, by using SNAP (which put the actual reading back on the perfect vector line), it removes the drift from all 3 axis. Now, some will say this hides a sloppy machine, and yes, it can, BUT, this example is a VERY exaggerated example of how much drift you might see. On my old (OLD! 20+ years old) machine, I get less than 0.002" of drift and that really won't show up unless you are trying to hold micron values.
I was explained in PCDMIS CAD++ class that snap point is to correct machine drift mathematically not hiding machine drift (at least that the impression that I got). Example:Blue print defined a point on a complex surface at XY exact position (basic dimensions) and the third axis (Z) must meet blue print requirement at that position. The snap point does just that by re-calculating the actual Z value at exact position (theoretical position).
I remembered the instructor said he was helping one of his customers measuring a complex curve surface using CAD and the DCC of the machine is very sloppy, the part they were checking is a known good part but the result proved otherwise he then suggested to use snap point and everything fall in.
Your explanation is exactly the same as stated in PCDMIS help file.
I have read many of your postings and I know you are among the very best in the country, I have no doubt of your assessment. I am just confused!!!
