Thank you all for responding, it seems the concensess are to dimple instead of CS. So, this is what I will plan on doing unless there is a compelling reason offered to do CS
If we specify a specific process in the construction manual it is always for a specific reason
Having said that, it is not always the only way to do something but we specifically choose one method after evaluating the options.
In this case it is for two reasons....
1. - Some builders do not do as good of a job of dimpling as could be done. This usually doesn't have a negative influence on the nesting of parts, but in this instance, it is 3 layers in a highly loaded area of the wing so M. C. was chosen to minimize the influence of that.
We are fully aware that mach. countersinking .032 material causes a knife edge on the hole which is why in Section 5 we specifically state that we recommend doing so for 3/32 rivets only on .040 or thicker material.
This is intended as a general rule of thumb that in very specific circumstances we may choose to deviate from (this case and a portion of the fuel tank skins being the only instances that I can think of at the moment).
As already mentioned, the area is flat enough that dimple countersinking all 3 parts is acceptable if the dimples are well formed.
2. - A slight reduction in dimpling work that needs to be done. The machine countersinking can be done when the skin and doubler are put into place for riveting