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Distance between 2 circles

ccorrell
So I'm dimensioning the distance between 2 cylinders. The cylinders are in the same workplane, ZPLUS. The cylinders are constructed by 2 circles, 1 at top of bore, 1 at bottom. What is the proper way of dimensioning distance between the 2? From Z-0, the first Cylinder has 2 depths of 18.75MM and 4.75MM, the second Cylinder has depths of 21.05MM and 10.7MM. Would the proper way be to use points and dimension 3D distance? I've dimensioned it a few different ways. I have a tolerance of +-0.0505MM

a) 2d distance from 2 cylinders = 0.0899MM short of nominal
b) 3d distance from 2 cylinders = same result (0.0899MM short of nominal)

c) 2d distance from circle from each bore = same result (0.0899MM short of nominal)
d) 3d distance from circle from each bore = same result (0.0899MM short of nominal)

e) 2d distance from a point constructed in each cylinder = (0.0377MM short of nominal)
f) 3d distance from a point constructed in each cylinder = same result (0.0377MM short of nominal)
  • Why would the cylinders have different depths? I presume there's stepped variations in diameter, maybe for receiving some type of AN style fitting or port?
    --If your print calls out one dimensional control for multiple features of size (multiple cylinder diameters) then your print has errors in it.
    --If your print is for an actual AN fitting, there's AN spec's for each step, you have to dig through some specs to find them, but they exist.

    Per GD&T, any point between centroids of either axis, for each feature of size, with distance measured at the same depth... should meet the distance requirement.
    Top circle, bottom circle, mid-axis point (like a cast point). etc, they all should meet the dimensional controls of the drawing.

    In my personal opinion, for situations like this where there's no FCF's demanding form or location control, I measure where the end of the dimension's extension line resides (at the top of the bore generally)
  • Why would the cylinders have different depths? I presume there's stepped variations in diameter, maybe for receiving some type of AN style fitting or port?
    --If your print calls out one dimensional control for multiple features of size (multiple cylinder diameters) then your print has errors in it.
    --If your print is for an actual AN fitting, there's AN spec's for each step, you have to dig through some specs to find them, but they exist.

    Per GD&T, any point between centroids of either axis, for each feature of size, with distance measured at the same depth... should meet the distance requirement.
    Top circle, bottom circle, mid-axis point (like a cast point). etc, they all should meet the dimensional controls of the drawing.

    In my personal opinion, for situations like this where there's no FCF's demanding form or location control, I measure where the end of the dimension's extension line resides (at the top of the bore generally)

    Actually it's for a Con Rod. The Crank side of the Con Rod I am measuring near the top and bottom of the bore. The Pin side of the Con Rod has an angled portion on top, and also a bushing inside, so I'm basically going off of the top and bottom portion of the bushing, since there is a groove right in the middle. Should I match the depths from the Pin side to the Crank side?

    Edit: When I say the Cylinder has 2 seperate depths, I mean depth from Z0, each depth where I measured a circle. The bore itself is all the same diameter. Sorry.
  • 2D distance centre to centre is the way to go.
  • If cylinders are not parallel, the distance between them is along the line which is perp to both axes, so its :
    ASSIGN/DISTANCE=ABS(DOT(CYL2.XYZ-CYL1.XYZ,CROSS(CYL1.IJK,CROSS(CYL2.IJK,CYL1.IJK))))
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