Best way to tolerence machined hole to center of boss?

[JoeBlock]

I have a product that is getting seven new holes added. It's more important that the holes be drilled in the center of their bosses (so the self tappers wont bust out the side) then the holes be positioned to [-A-], [-B-], [-C-].

Should I call each boss a datum tolerenced to A/B/C and then toerence the drilled hole to it's datum (boss)?

Or can by tolerencing each boss to A/B/C and then say their holes must be concentric to them?

Thanks

 

[ewh]

Fosters guides are very good, but it always helps to have the actual standard to address areas he doesn't cover in fine detail.

 

[JoeBlock]

Hope this link works. Sent a jpg to ebay picture. Let me know if OK.

http://i10.ebayimg.com/02/i/07/96/07/f1_1_b.JPG

 

[ewh]

You still need to specify "7X INDIVIDUALLY" next to the datum callout.

 

[JoeBlock]

Thanks for checking it out. How about this one or does 7x INDIVIDUALLY need to be in both spots.

http://i4.ebayimg.com/04/i/07/93/f1/03_1_b.JPG

 

[ewh]

Yes, it needs to be in both spots.

 

[JoeBlock]

Special thanks to ewh and aardvarkdw. I submitted with confidence

Thanks to all.

 

[Tunalover]

First locate the bosses using either a single line positional tolerance fcf or a two-line composite pt fcf. It's not necessary to call out the boss size with the pt fcf. The boss size can be shown elsewhere.

Next, to locate each hole coaxial to its boss you need what's called a "repeated datum." Do a section view of the boss and add the multiplier 7X to the view caption or to the section lines in the parent view. Assign a datum to the boss diameter, call it -D-. In the section then call out the hole size with a pt fcf using -A- as your primary datum (assuming -A- is assigned to the perpendicular surface and you want it be your primary datum) and -D- as your secondary. Note that both the hole and the boss are features of size so you can gain bonus tolerances by judiciously using material condition modifers (sometimes needs some soul-searching as to which ones to use). Under the pt fcf for the hole add the note INDIVIDUALLY. To the -D- datum symbol add the note INDIVIDUALLY. The multiplier e.g. 7X is not necessary as it has already been assigned to the section.

Tunalover

 

[ewh]

Adding a section that is typical 7X is cetainly another way to do it. There's always more than one way to skin a cat