[PCB_FORUM] Re: Tooling holes

re: At our internal assembly, these are _only_ used in assembly on an "old" stencil screener. 
At our internal assembly these board-level tooling holes are used
a) to jig the press operation for inserting press-fit connectors and
b) to jig the in-circuit test clamshell

-Gary Carter

Mark Salberg wrote:

Hello Group,
This is regarding tooling holes.

We are required add 2, 3 or 4 .125 NP "tooling" holes.
NP normally used for tighter hole size tol (+/-.002")
Also tooling hole to tooling hole location tol =+/- .003".
At our internal assembly, these are _only_ used in assembly on an "old" stencil screener. 

Questions:
*1.* Do fab vendors use these for fab tooling or do they use their own from the fab panel. 
(i.e.) stack-up, registration, test during fab, etc...

*2. *Is it _necessary_ to have a NP hole as a dimension datum?
We normally do, but if I have a board (ex) all PTH with plated mounting holes...should I _add_ a NP hole just for a dimension datum?
I believe that the center of a plated hole is as close in tol location as a NP hole. but the finished hole size is tighter on a NP hole. 

Regards,
Mark

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