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Cylinder Min Value compared to Max Inscribed

mgroll77
I was asked if the measured max inscribed value of a circle/cylinder should be the same as the minimum value measured for that same circle/cylinder.

As far as I understand it, a max inscribed value of a hole is based off of the 3 inner most points to a circular axis. It's the largest virtual or actual pin that will fit in the ID. The minimum value is the point closest to the circular axis, (radius*2). Sometimes max inscribed and min value are the same, sometimes not.

What am I missing.
  • Sometimes max inscribed and min value are the same, sometimes not.



    If you measure a circle with 3 hits, you will have the same result !!!!!
    I don't know about measured circles, but for auto circles or constructed circles, the values are different (for more than 3 hits).
    If it doesn't work for measured feature, you can create circles from hits and look at the result (CIR1.HIT[1..CIR1.NUMHITS])
  • What is your definition of "minimum value" of a circle?

    When PC-DMIS gives me a report, it includes: MEAS, NOM, +TOL, -TOL, MAX, MIN, DEV.
  • If you measure a circle with 3 hits, you will have the same result !!!!!
    I don't know about measured circles, but for auto circles or constructed circles, the values are different (for more than 3 hits).
    If it doesn't work for measured feature, you can create circles from hits and look at the result (CIR1.HIT[1..CIR1.NUMHITS])

    I am measuring a cylinder with 12 hits, 2 levels.
  • Is the cylinder you are measuring an inside (hole) or outside (post) feature?
  • Maximum Inscribed – This calculation type generates an empty circle with the largest possible diameter that lies within the data. PC-DMIS first computes a Minimum Circumscribed circle and requires that the center of the Maximum Inscribed circle lies within it. This option could be used for a circular feature that requires a mating stud. For example, if the input data represents a hole, then this calculation returns a circle with the diameter of the largest stud that will fit inside the hole.

    This is right out of the pcdmis help file. It also has a explanation for the other 4 types of circle measurments. If your measuring with 24 hits as I understood in posts above. Try a odd number of hits this may give you some different results hth
  • I am measuring a cylinder with 12 hits, 2 levels.

    Cylinders should always (circumstances allowing) be measured with 3 levels to generate a proper vector for the centre axis.
    You should also use an odd number of hits per level (total number depends on size of hole and tolerancing requirements).
  • I was asked if the measured max inscribed value of a circle/cylinder should be the same as the minimum value measured for that same circle/cylinder.

    As far as I understand it, a max inscribed value of a hole is based off of the 3 inner most points to a circular axis. It's the largest virtual or actual pin that will fit in the ID. The minimum value is the point closest to the circular axis, (radius*2). Sometimes max inscribed and min value are the same, sometimes not.

    What am I missing.

    Nothing. You are correct. If they happen to give the same value then it is coincidental.
  • Cylinders should always (circumstances allowing) be measured with 3 levels to generate a proper vector for the centre axis.
    You should also use an odd number of hits per level (total number depends on size of hole and tolerancing requirements).

    Thanks for the suggestion. I'll start practicing this when developing cylinders.
  • Nothing. You are correct. If they happen to give the same value then it is coincidental.

    Thanks for the confirmation Rondog.
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