![]() ![]() The geometry best fit is being used to allow the actual values to be rotated / translated along/around the unconstrained axes to their best position relative to the nominal position of the feature rather than simply taking the default position relative to the base alignment.According to the ISO Geometrical Product Specification (GPS), a primary common datum plane of a part with two parallel offset planes is established by two datum targets on one plane and one datum target on another parallel plane. The degrees of freedom it does not constrain are currently coming from the Base Alignment. So it really depends what your primary datum feature is and what it is constraining. If the DRF only contained the cylinder as primary, then it would be acceptable to allow best fit along Z and around Z, in the case of the cylinder primary and plane secondary then it would only be acceptable to allow best fit of rotation around Z ![]() So lets say you had a Cylinder as your primary datum that controlled translation in X and Y and rotation about the X and Y axis, that would leave translation along Z and rotation around Z unconstrained, now lets say we have a secondary datum that is the plane at the end of the cylinder, it would control translation along the Z axis but leave rotation about Z unconstrained. any 2nd or 3rd opinions on this?Ī geometry best fit may be used even when there are Datum's called out, the only thing you need to remember is you can only best fit the translations or rotations that are NOT controlled by the Datum Reference Frame. Adam's Geometry Best Fit Alignment "feels right". My understanding is that you CANNOT use "Best-Fit" when there is a datum involved?īut. The rest of the part is in tolerance, with similar tolerances. The delta is about 0.0006/0.0007 (inches), which about half my total tolerance. How large (or small) is the Delta value of your results?ĭid you test the repeatability of the measurements with any specific base alignment (without changing)?Ĭan you post pics of just the alignments that you are using? My preferred method of checking something like this is to create an alignment that uses Datum A as the spatial rotation, and Z origin, and create a geometry best fit alignment that references the Datum A alignment, and use that best fit to profile the pocket. When creating a profile characteristic, and entering Datum A as the primary, secondary and tertiary datums, it seems that I can get different findings based on how I set up my base alignment, which shouldn't be impacting anything, but looks to be influencing rotation. Essentially, they want the pocket perpendicular to Datum A. I have a small, shallow rectangular pocket that's profiled to just one datum, it's top face, which we'll call datum A. ![]() Is my best fit alignment strategy the best approach? ![]() How can I keep the base alignment from being a contributor in a single datum FCF?ģ. My preferred method of checking something like this is to create an alignment that uses Datum A as the spatial rotation, and Z origin, and create a geometry best fit alignment that references the Datum A alignment, and use that best fit to profile the pocket.Ģ. I have a small, shallow rectangular pocket that's profiled to just one datum, it's top face, which we'll call datum A. I can't post pictures, so I'll do my best to explain it. I'm sure this has been covered, but as the search function is set to ignore most input, I'll just ask. ![]()
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