True position to a plane only

[DB not cooper]

Hey all,

I have a part with 1 large center bore and 7 bolt holes around the center bore, one of the Position callouts is the 7 bolt holes to the face only, now I know if it was one hole it would be perpendicularity, but with 7 holes on a bolt circle i'm supposed to position them to themselves. now the best way I can think to do that is use the face for level and Z0 then use one of the bolt holes for rotation but what should I use for a center? would I use the center bore or the center of the bolt circle?

[Schlag]

You would be a best fit alignment to all of the holes. You don't want 1 hole as a zero, that shifts all the error to the other holes. Based on how this would be manufactured that error probably wouldnt make it a bad part but might as well get the most out of the callout. Perp still applies to this.

[Cumofo]

Heck yeah man, Level=datum plane, two holes 180 apart=rotation, bolt circle=center. Measure the features as cylinders so the tolerance is correct per ISO. Give 'em what they want, and don't think about it too much!

[DB not cooper]

I tried it that way and it worked well. thanks!

[NinjaBadger]

Heck yeah man, Level=datum plane, two holes 180 apart=rotation, bolt circle=center. Measure the features as cylinders so the tolerance is correct per ISO. Give 'em what they want, and don't think about it too much!

There are 7 holes so none are 180° apart.

You should level to plane and origin on it, leave origin on centre bore (initially) then best-fit (2d, rotate and translate) then report positions that way.