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Circle scan not centered.


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Hello everyone, 

I was wondering if someone could help me out with this. So the part I am inspecting, I have true position call outs for 6 different holes with a 0.002 tolerance. My issue is that all my scans are coming out skewed and throwing the tolerances way off. The results for true position are 0.085-0.090, but dimensionally are correct. I know these parts are not that far out. But why does the scanning area look so skewed or not centered to the hole? And would that be causing my tolerances to be that far out? Thank you for any assistance. 

Lou

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If you right-click on the screen and go to curve magnification, that might be turned up too high. But, what you are describing sounds like the holes are out of position. How is .085-.090 dimensionally correct? If you are confident that the positions not as bad as the results you are getting, it could be a lot of things. It could be the probe calibration or an alignment issue. I would first, extract a new circle from the CAD, measure it, and see if it's still bad, and compare the nominals.

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Couple things here, and I am not picking on you. We all started at the beginning. Your tolerance zone is a set number, in this case 0.002 (inches?). It is difficult to understand when you say the results indicated a position error of 0.085-0.090 (inches) but are the correct dimensions. This can not be the case. Unless you mean the basic dimensions are verified correct nominal?

The position of the holes in relation to what?

A little bit more information is needed here to help point you in the right direction.

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For me it looks like bad base alignment if those parts are not that bad. Or unstable alignment.

Do manual recheck of one of holes - run program ( not in autorun ) and after finish go and take 3-4 points on one of incrimined holes to get it's nominals ( automatic recognition ).

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Are you possibly using additional alignments and are the dimensions perhaps measured in those additional alignments? If so, be aware of the fact that everything you see in the CAD window is transformed to the base alignment. So a basic Calyps basic rule is: whenever additional alignments come into play, don't trust any (graphical) deviations you see in the CAD window without further checks. The CAD display can be very misleading at times.

That does not mean this is the reason for the deviations, it's just a - possible - graphical glitch.

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Something ain't right here. Are you sure you aren't measuring the feature to one set of coordinates and the characteristic to another? Also, is this dimensioned to cylindrical coordinates (often erroneously called 'polar' coordinates)? If so, are you using decimal degrees or deg/min/sec? Are you possibly getting lost in adding angles?

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This looks like a threaded hole for which you should be using at lest 4 lines of scanning vertically. This should give you more coverage on the hole along the threads.

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