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Crazy Diameter (math error)

Edit: reducing the hits to 3 INCREASED the accuracy of my measurements. Special thanks to UKCMM!




So I was measuring a cylinder and I got some pretty crazy results (See the diameter). Trying to figure out why this happened beyond some good ol' fashion PC DMIS math magic: none of the hits seem to be varying a crazy amount (at least not WHOLE INCH level of crazy) so I was wondering if any of the experts out there had some insight into how this could have happened so I can avoid it in the future without having to just remeasure the feature until it works.


Code:

LEFT_CUTOUT =FEAT/CONTACT/CYLINDER/DEFAULT,CARTESIAN,IN,LEAST_SQR
THEO/<-3.6115,0.601,3.8812>,<0.943801,0,0.3305144>,0.2,-0.125
ACTL/<-3.4513,20.3725,4.1557>,<0.9510529,-0.0114305,0.3088165>, 39.6259,-0.125
TARG/<-3.6115,0.601,3.8812>,<0.943801,0,0.3305144>
START ANG=0,END ANG=-180
ANGLE VEC=<-0.3305144,0,0.943801>
DIRECTION=CW
SHOW FEATURE PARAMETERS=YES
VOID DETECTION=NO
REMEASURE=NO,USE THEO=NO
SURFACE=THICKNESS_NONE,0
MEASURE MODE=NOMINALS
RMEAS=LEFT_NOTCH,LEFT_EDGE,LEFT_NOTCH
AUTO WRIST=NO
CIRCULAR MOVES=CIRCULAR
GRAPHICAL ANALYSIS=NO
FEATURE LOCATOR=NO,NO,""
SHOW CONTACT PARAMETERS=YES
NUMHITS=8,NUMLEVELS=4,DEPTH=0.02,END OFFSET=0.02,PITCH=0
SAMPLE METHOD=SAMPLE_HITS
SAMPLE HITS=0,SPACER=0
AVOIDANCE MOVE=NO,DISTANCE=0.3937
FIND HOLE=DISABLED,ONERROR=NO,READ POS=NO
SHOW HITS=YES
HIT/BASIC,<-3.6257,0.6045,3.9821>,<0.330313,-0.0348995,-0.943226>,<-3.615,0.5995,3.9847>
HIT/BASIC,<-3.622,0.6466,3.9718>,<0.2941154,-0.4562107,-0.8398619>,<-3.6114,0.6426,3.9746>
HIT/BASIC,<-3.6128,0.6801,3.9455>,<0.2021837,-0.791071,-0.577346>,<-3.6024,0.6772,3.9482>
HIT/BASIC,<-3.5998,0.6986,3.9084>,<0.0719386,-0.9760254,-0.2054245>,<-3.5888,0.6971,3.9098>
HIT/BASIC,<-3.5854,0.6986,3.8673>,<-0.0719386,-0.9760254,0.2054245>,<-3.5738,0.6981,3.8662>
HIT/BASIC,<-3.5724,0.6801,3.8301>,<-0.2021837,-0.791071,0.577346>,<-3.5599,0.6782,3.828>
HIT/BASIC,<-3.5632,0.6466,3.8038>,<-0.2941154,-0.4562107,0.8398619>,<-3.5507,0.6434,3.8012>
HIT/BASIC,<-3.5596,0.6045,3.7935>,<-0.330313,-0.0348995,0.943226>,<-3.5473,0.5999,3.7912>
HIT/BASIC,<-3.5329,0.6045,3.8029>,<-0.330313,-0.0348995,0.943226>,<-3.5205,0.5999,3.801>
HIT/BASIC,<-3.5365,0.6466,3.8132>,<-0.2941154,-0.4562107,0.8398619>,<-3.524,0.6432,3.811>
HIT/BASIC,<-3.5457,0.6801,3.8394>,<-0.2021837,-0.791071,0.577346>,<-3.5334,0.678,3.8378>
HIT/BASIC,<-3.5587,0.6986,3.8766>,<-0.0719386,-0.9760254,0.2054245>,<-3.547,0.6975,3.8759>
HIT/BASIC,<-3.5731,0.6986,3.9177>,<0.0719386,-0.9760254,-0.2054245>,<-3.5619,0.6968,3.919>
HIT/BASIC,<-3.5861,0.6801,3.9549>,<0.2021837,-0.791071,-0.577346>,<-3.5756,0.6768,3.9571>
HIT/BASIC,<-3.5953,0.6466,3.9812>,<0.2941154,-0.4562107,-0.8398619>,<-3.5844,0.6421,3.9833>
HIT/BASIC,<-3.5989,0.6045,3.9915>,<0.330313,-0.0348995,-0.943226>,<-3.588,0.5995,3.9936>
HIT/BASIC,<-3.5722,0.6045,4.0009>,<0.330313,-0.0348995,-0.943226>,<-3.5608,0.5994,4.0016>
HIT/BASIC,<-3.5686,0.6466,3.9905>,<0.2941154,-0.4562107,-0.8398619>,<-3.5574,0.6417,3.9917>
HIT/BASIC,<-3.5594,0.6801,3.9643>,<0.2021837,-0.791071,-0.577346>,<-3.5485,0.6761,3.9658>
HIT/BASIC,<-3.5463,0.6986,3.9271>,<0.0719386,-0.9760254,-0.2054245>,<-3.5355,0.6962,3.9285>
HIT/BASIC,<-3.5319,0.6986,3.886>,<-0.0719386,-0.9760254,0.2054245>,<-3.5203,0.6964,3.8851>
HIT/BASIC,<-3.5189,0.6801,3.8488>,<-0.2021837,-0.791071,0.577346>,<-3.5067,0.6772,3.8475>
HIT/BASIC,<-3.5097,0.6466,3.8226>,<-0.2941154,-0.4562107,0.8398619>,<-3.4975,0.643,3.821>
HIT/BASIC,<-3.5061,0.6045,3.8122>,<-0.330313,-0.0348995,0.943226>,<-3.4937,0.5997,3.8103>
HIT/BASIC,<-3.4794,0.6045,3.8216>,<-0.330313,-0.0348995,0.943226>,<-3.4683,0.5997,3.8234>
HIT/BASIC,<-3.483,0.6466,3.8319>,<-0.2941154,-0.4562107,0.8398619>,<-3.4716,0.6416,3.8327>
HIT/BASIC,<-3.4922,0.6801,3.8582>,<-0.2021837,-0.791071,0.577346>,<-3.4805,0.6749,3.8589>
HIT/BASIC,<-3.5052,0.6986,3.8954>,<-0.0719386,-0.9760254,0.2054245>,<-3.4936,0.6943,3.8956>
HIT/BASIC,<-3.5196,0.6986,3.9364>,<0.0719386,-0.9760254,-0.2054245>,<-3.5083,0.6942,3.9372>
HIT/BASIC,<-3.5326,0.6801,3.9736>,<0.2021837,-0.791071,-0.577346>,<-3.5215,0.6746,3.9743>
HIT/BASIC,<-3.5418,0.6466,3.9999>,<0.2941154,-0.4562107,-0.8398619>,<-3.5299,0.6405,3.999>
HIT/BASIC,<-3.5454,0.6045,4.0102>,<0.330313,-0.0348995,-0.943226>,<-3.5338,0.5994,4.0107>
ENDMEAS/

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  • It could be that as the length of the measured cylinder is very short ( 0.080" ) compared to diameter, you are only measuring 180 degree of diameter and it is at an angle then the software maybe having problems resolving the hits.

    With this small feature I have found that less hits can yield better sometimes results.

    You could try reducing the number of hits to 3 and levels to 3, if you cam increase the length of the measured cylinder to the max possible. Also are the cylinder vectors correct they just seem a little odd and is the probe at the right angle to prevent shank out.

    lastly Happy new year
  • Yeah its a cutout on an angled surface, so the vectors are correct for that surface. The length is .125" with .02" offsets on both ends, is that the .08" length you're referring to? The material thickness is only .125" unfortunately but I will definitely try reducing the hits
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