Symmetri on internal slot - best practice

[[To...]]

I am not very familiar with doing this kind of inspection, and I do not trust my results, so I thought I would ask in here instead.

I have made a very bad 2D drawing, but I think you get the idea. It is a cylinder wit a length of 150mm and the slot has the same length.
The height of the slot is about 5 mm.

My base alignment is as the red letters show, A is a cylinder, B is a plane and C is a line.

I measure the side of the slot as to planes, but the planes are both only having a width of 1mm and I believe this could be the problem.

How would you do this task?

example.png

[[Lo...]]

Check the planes as lines then recall a 3D line from those measured lines. Then check the line back to -A- datum. You may not be able to report it as a symmetry but you can report where the 3D line is to your Datum -A-'s centerline. I've done that in the past. Hope that helps.

[[Mi...]]

Sometimes you can slip some gauge blocks into the slot and measure those instead to get more area. It doesn't always repeat that well, though, depending on the form of the slot, but it's a start at least.

[[Re...]]

If by chance you are not looping your base alignment, I would suggest doing so. It was many years ago measuring a part with a similar callout and no fixturing that I learned the value of looping to fine tune the vectors.

[[Ün...]]

I'm using a point of symmetry for "C" in a similar piece. With one point each for the right and left plane. And I add loop.

[[Aa...]]

Seeing as how the Symmetry FCF does not reference any datums that would put any constraint on the clocking about the axis of A, an alignment that best fits in that DoF is in order.