[Ri...] Posted March 8, 2021 Share Posted March 8, 2021 I remember a thread on this topic sometime ago, but I am unable to locate it. The post basically contained a chart that illustrated that as arc length decreases uncertainty increases. I have some extremely thin and relatively small punched diaphragms with some tiny radii segments (R .0075" ±.0025") that present only 23°-29° of arc radius for measurement at best. The parts themselves exhibit poor form due to the manufacturing process and its proving extremely difficult to get a size/position that I can feel comfortable reporting. Even with a 3D optical profilometer I don't think there's enough meat to work with. Anyone know where I can find a similar chart to the one I described so I can demonstrate to my handlers that the inspection method with such a small feature size is perhaps dubious at best? Feature https://ibb.co/MCW7hvm Arc Radii Segments https://ibb.co/0G0qD4V Link to comment Share on other sites More sharing options...
[Ch...] Posted March 8, 2021 Share Posted March 8, 2021 in characteristic, right click ... Constrain XYZ of feature eval to find best size (provided nominals are correct, from CAD model, etc.) Constrain Rad to find accurate XYZ location. Try single points vs scanning for your best result. Either should work well, but just for your own comparison. Good luck. Link to comment Share on other sites More sharing options...
[Jo...] Posted March 8, 2021 Share Posted March 8, 2021 You could make Profile of a line with segment tolerances . That would provide a reasonable graphic representation. Link to comment Share on other sites More sharing options...
[Ri...] Posted March 8, 2021 Author Share Posted March 8, 2021 I found this which is pretty close to what I was looking for. Illustrates uncertainty and small angle of arc/point density https://ibb.co/fv0BPnb Link to comment Share on other sites More sharing options...
[Cl...] Posted March 9, 2021 Share Posted March 9, 2021 Yes, constraints and single points! Link to comment Share on other sites More sharing options...
[Ke...] Posted March 9, 2021 Share Posted March 9, 2021 Please sign in to view this quote. Can you provide a link to the source material for this image? Given that the form is poor, as you mentioned; I wonder if there may be a benefit to comparing the profile (with no datum controls), to show the part-to-part variation, on a set of samples (in conjunction with actual results, using a couple of different methods). Link to comment Share on other sites More sharing options...
[Ri...] Posted March 9, 2021 Author Share Posted March 9, 2021 Please sign in to view this quote. National Physics Laboratory Good Practice Guide No. 41 CMM Measurement Strategies By David Flack Pg. 60 https://www.npl.co.uk/special-pages/gui ... m.pdf?ext=. Link to comment Share on other sites More sharing options...
[Ri...] Posted March 9, 2021 Share Posted March 9, 2021 Please sign in to view this quote. Profile of a Line is a much better control of the radius. I've also had good luck measuring the feature as a Curve, creating a Best-Fit alignment from the Curve, and measuring the Circle with single points constrained to the location of the Curve. The biggest problem with constraints is that you are assuming that the feature is where you think it is, most likely it isn't. If it's a corner wall radius, you can also construct a simple alignment from a point on either side. Small arc radii are a pain in the butt, even on machines designed to measure them like Contour Tracers. Link to comment Share on other sites More sharing options...
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