Symmetry and DRF

November 6, 2021

I have to check symmetry w.r.t datum A_B. When I check symmetry w.r.t datum AB( stepped cylinder), I got 0.04. I created a secondary alignment by spatial datum AB and planer top plane, a completely constrained DRF. Using this alignment I got symmetry 0.314. I know according to drawing I should use datum AB only.But this is a correct method?. Symmetry control location and orientation, using datum AB we can control only location , can't control the orientation of the cylinder. My question is for symmetry rotational degrees of freedom is to be completely constrained??. Which one is correct results 0.04 or 0.314.

IMG_20211106_220644.jpg

November 6, 2021

First of all - A-B is not stepped cylinder.

For symmetry i don't know if you can select another alignment. But seem like they don't care about perpendicularity with that plane as long as 20+/- 0,1 is good.

For full alignment i would cut cylinder 8 J6 in center to get rotational point.

November 8, 2021

I have a symmetry query similar to this one. I'm using a cylindrical step and it's very successful. (A-B)
0.04 should be correct according to this picture.

November 8, 2021

Recalling points from cylinders into 1 cylinder is probably how I would approach this. A step cylinder would be used if cylinders were different sizes.

I'm not 100% sure but I believe when you apply the symmetry to the cross cylinder, it may be doing a best fit rotation about the A-B axis until cross cylinder axis is straight, i.e. parallel to Z axis per view shown. When you add the planar, it is restricting the rotation and improving the result.

November 8, 2021