Radius Accuracy

[[Da...]]

I am looking for ways to improve the measurement of Radii. The parts I have were cut on a wire EDM machine and are typically 2-5" " wide with a radius 10-15" +/- .002" radius cut on one side. I have tried changes to the speed as well as the number of points etc. without much consistency or accuracy. Obviously, the smaller the segment of the circle, the harder to check. I know it isn't just me because other vendors we have used have mentioned similar problems. Could it be the finish or am I missing something in terms of parameters?

[[Jo...]]

There will be loads of suggestions on methods, but this is a math problem really. You are extrapolating answers from little data.

Here is a tool I use. Measure the surface and recall into freeform. Use profile of surface with no datum to evaluate. This will give you a heat map of form based on cad geometry. There are various methods to extract radius dimensions, but profile really communicates the form.

[[SH...]]

Hope you are working with cad model and do scanning.
Constrain the co ordinate value in the evaluation tab.
If you have contour tracer , you will get a better results.

[[Cl...]]

I like using single probing points with coordinate constraints.

An old but reliable trick is to find the center of the radius, probe a point there. Make that your XYZ origin. Then translate back the nominal radius and create a second alignment there. Now change to polar coordinates and probe single points on the radius surface. This will give the most accurate information. There might be a better/faster way within Calypso. I used to do this years ago in Virtual DMIS.

[[An...]]

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[[No...]]

Decades old (originally) and still only available in German, but nevertheless worth reading:

http://www.dr-hernla.de/Hernla%20Info%2 ... chnitt.pdf

[[SH...]]

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Creating a small curve, and recall it to a circle would not be better??

[[Ro...]]

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I agree with Clarke.
When dealing with very small segments of radii or spheres or cones or cylinders, i have used single points in the past and got good results. but if you have a couple degree slice of a 15 inch Radius and are trying to hold +/-.002 tolerance, then the deck is already stacked against you. You're fighting city hall.
Try converting your scan segment to 10 touch points and see if that helps at all.