[Am...] Posted August 21, 2020 Share Posted August 21, 2020 Hi everyone, im getting a profile that is reading way out and there is just no way its correct. The left edge there is Datum C, long side is Datum B and the curved surface is datum A. Ive tried this a couple different ways using curve for A and I still get around .500". The profile is to ABC, the C datum has a profile callout to AB and i get that in but the right side to abc keeps coming in way out. My form on all datums is about .0001". What is going on here? Link to comment Share on other sites More sharing options...
[Am...] Posted August 21, 2020 Author Share Posted August 21, 2020 I know datum a is ridiculous the diameter of the curve is over 45 inches, but seems to be working ok everywhere else ive used it. Link to comment Share on other sites More sharing options...
[Cl...] Posted August 21, 2020 Share Posted August 21, 2020 In your Base Alignment, I wonder if you might need to "balance" the part about the Y axis? E.g., two points at the same (X+/X-) coordinates to planar rotate? As the alignment stands currently, you could test that out by just probing a point at X+ & X- and comparing the Z values. Link to comment Share on other sites More sharing options...
[Da...] Posted August 22, 2020 Share Posted August 22, 2020 Why not scan A as a surface and use the surface as a datum? No need to calculate a cylinder from insufficient data. You’ve had the right intuition there, A as a cylinder is ridiculous. Besides: A as a cylinder and primary datum takes away four degrees of freedom, which is mighty powerful for an element based on such a small section. It would only leave two DOF for B and C, which would only be a translation and a rotation around the cylinder‘s axis (pretty much useless in this setup). A as a surface would only constrain three degrees of freedom and would be much more stable. B would provide a rotation and translation and I’d say that might be the designer's intention. Link to comment Share on other sites More sharing options...
[Ro...] Posted August 24, 2020 Share Posted August 24, 2020 Show a screenshot of the results, the arrows that show the form err. Link to comment Share on other sites More sharing options...
[Jo...] Posted August 25, 2020 Share Posted August 25, 2020 Very likely the result is correct. The origin of measurement is from the axis of datum feature A and since you have such a tiny piece of the overall cylinder, the axis is just not calculating well. There's a TON of uncertainty in this measurement. Link to comment Share on other sites More sharing options...
[Am...] Posted August 26, 2020 Author Share Posted August 26, 2020 Please sign in to view this quote. oh I know, thats why i've tried a bunch of secondary alignments doing doing a best fit of several curves for Datum A has actually worked really well, the other side comes in within .010" while the other side is coming in at .500". This was a second program that I made to check Datum A in a free state and i threw these on there too, Its a lot better in the fixture with simulated Datums to constrain the part to but im covering like half the side so I wanted to do those in the free state. Link to comment Share on other sites More sharing options...
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