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Width vs Midplane and positional tolerance

I'm trying to understand this width vs midplane non-sense.

From what I understand midplane is simple, you collapse two parallel planes until they hit the highs of the opposing planar surfaces and bingo you have a center plane from this perfect datum simulator.

I would think width feature is the same methodology except you get an additional width measurement from it....so then I think....why have two separate tools for this. Just let midplane kick out the width....so I tend to believe there is some 'centroid' craziness going on with the width feature...if I'm correct does it then matter how dispersed your hit points are? If you collect them too much on one side have you pushed the centroid to one side?

I was abused by pcdmis as a metrology child b/c I just never really understood this love affair with the centroid. So if someone could slap me around a little that would be appreciated.

Secondly, then how do you properly do a positional MMC callout of a centerplane(from a feature of size). You need the width to get the bonus and b/c you need a feature of size, but you need to create a centerplane at the same time? So I'm confused here as well. I also see the width reported back an X,Y,Z location.....is this simply reporting a single point in space b/w the centroids?

Thank you.
  • I would say mid-plane is only the plane that averages the position and the angle between two planes, whatever the number of hits of each one, and whatever the algoritthm used for each one.
    If yo have a datum on a width, then using a mid plane is a bad solution because the plane that represent correctly the datum is the mid plane of 2 parallel planes that fit the width, on the external side of the material (so you have to use minsep for the width).
    IMO.
  • If you take 100 hits on one side's plane and 10 on the other, the centroids will still be laying on each plane and not be 'pushed to one side' when you make the midplane.

    You can use the width feature created to do your position on, so no need for a midplane. You can apply MMC to it when dimensioning, as well.

    A width will only use one basic for its position.

  • post the code, too many variables for us to make a solid answer.