Dimensioning a bolt circle as a radius

[310toumad]

Let's say you have a cylindrical part. When looking down the axis of the part, along the circumference picture several round "ears" protruding. At the center of each ear is a hole (imagine this part as being a casting).

The problem is I'm not sure how to dimension the bolt circle of the holes because their centers lie on a B.C. with a diameter that is very close to the O.D. of the cylindrical part itself. So when you draw the B.C., its hard to distinguish between it and the physical, solid line that represents the part surface. I cannot change the part or location of the holes to further 'offset' these two diameters to solve this problem.

One way I thought of to make it more clear was to have a small arc pass through the center of each hole, but this arc does not extend past the ears. Then I dimension one of the arcs as a radius, with the leader extending back to the center of the diameter. The radius is listed as basic. This makes it easier to distinguish the B.C. diameter line from the part O.D. line, since they don't overlap. I wanted to get some opinions on whether or not this method leaves the location of the other holes ambiguous, because without the arcs of the other holes also being dimensioned, you would essentially have to assume that they are co-radial with one another. Do I need to include an 'X' before the one basic dimension? Is there a better way to do this? Thanks.

 

[chez311]

That sounds like an acceptable solution to me. "nX" before the radial basic dimension might be wise to show that it applies to "nX" features.

 

[pmarc]

Another option could be to use basic linear dimension between the axis of the part and the center of the hole with 'nX' before the dimension value.

 

[TheTick]

Why not just put "OD" on the OD and "BOLT CIRCLE" on the bolt circle.

 

[Burunduk]

You could show a large scale detail view, indicated nX before the view designation (for example "10X Detail D") of one of the ears and the hole inside it but without the OD, an arc through the center of the hole, dimensioned with basic diameter (forshotened diameter dimension line displayed with just one arrow).