I need to measure a dimension to the centerline of a radius, but the radius is 2" and only covers an arc of about 25 degrees. Measured on the optical comparator, the radius is nearly nominal, but on the CMM it measures 2.117". This throws my centerline over .100" out of position. How can I create a centerline from points on the radius using the nominal radius? Can I force PC-DMIS to best fit a 2" radius to points on the surface?
Are you saying that the dimension is coming out lousy while offline? If so I am not sure how that is happening, but if you are able to repeat your radius (size) by using one of the methods you described, as well as your X and Y then that should be a pretty accurate indicator.
When I want to verify something of this nature, I usually create a generic circle at the specified print coordinates and set my x, y origin to it. I then get the x and y location of the measured feature from the new origin as well as the graphical comparison. It is a good idea to check your individual points to this known feature using polar radius, because what I have noticed in the past especially depending on the size of the feature is that no matter how many vector points you have, if you construct a circle on them it will still use the average rather than all of your point data and if you start out with the radius (size) in an untrue state the locations will be erroneous every time.
In fact I just had to do this same excercise this morning as I had to prove that a feature was 1mm out of position.
BTW, who in the world would put a true position on a radius? Wouldn't a profile be more suitable? As Jim Jewell said, and many of the apps engineers at Brown and Sharpe will tell you that this is a math problem.
Are you saying that the dimension is coming out lousy while offline? If so I am not sure how that is happening, but if you are able to repeat your radius (size) by using one of the methods you described, as well as your X and Y then that should be a pretty accurate indicator.
When I want to verify something of this nature, I usually create a generic circle at the specified print coordinates and set my x, y origin to it. I then get the x and y location of the measured feature from the new origin as well as the graphical comparison. It is a good idea to check your individual points to this known feature using polar radius, because what I have noticed in the past especially depending on the size of the feature is that no matter how many vector points you have, if you construct a circle on them it will still use the average rather than all of your point data and if you start out with the radius (size) in an untrue state the locations will be erroneous every time.
In fact I just had to do this same excercise this morning as I had to prove that a feature was 1mm out of position.
BTW, who in the world would put a true position on a radius? Wouldn't a profile be more suitable? As Jim Jewell said, and many of the apps engineers at Brown and Sharpe will tell you that this is a math problem.
