I have been putting a hole/circular cut to define the slot centers, then
coming in and cutting the slot as the next feature, referencing the hole
to control size.
This gives me all the centerlines on the drawing at the correct position
and direct access to dimensions for the location of the slots and their
centers.
Maybe overkill, but it works.
You could be lazy and bypass trying to show centerlines, and create a
dimension referencing centers or mid points of the flat geometry.
Sheet metal has a bug (in my opinion) in that it can not properly
position created axes in a flat view, whether model or drawing, as long
as I have used it.
It does not handle the bend allowance or the change in location due to
being on different surfaces/planes properly.
Seems like a basic math error, but I guess it has not been a priority,
so be careful and don't reference created axes in sheet metal for
dimensions.
Maybe someone has a better idea?
Regards,
Walt Weiss