I don't know what this true position on the hole is constraining. Bolt circle diameter or orientation of the hole maybe? Trying to determine if I need to measure the hole as a cylinder. Appreciate the help.
Disagreements are fine. Fundamental problem is the disconnect between design & mfg. In our place our team has been inspecting to the mfg for years because more often than not our designers don't have full understanding of machining vagaries & how GD&T plays its role in mfg & assembly.
GD&T is a design standard, not a manufacturing or inspection standard. I do agree that often inspection and manufacturing often have a better understanding of the subject. However, doing an end run around design is often the cause of the bickering. Manufacturing, quality and design have to have a common understanding of the requirements and how they are communicated. It will take a lot of hard work on all parties part to get there.
I did not read the whole thread, but skimmed. I think you want to remove the diameter symbol just before the dimension tolerance. Note that your print does not have that.
Using a cylinder as a primary datum is fine provided it is of sufficient length. Notice the distance between datum cylinder A and the flange is longer than the length of the cylinder. This can lead to projection errors.
Finding the cause can be difficult sometimes. I always start with my probes. Whenever possible use one probe for your alignment and critical features. You may want to check the perpendicularity of the cylinder to the flange plane.
This is the true position for pattern of 6 holes. you have to create all 6 holes. Then, construct a large circle pass through all holes. This is the true position for large circle which connects all holes through their origin. To find the true position of this pattern at once is normally with reference to Datum-A, and it should be better to find in legacy dimension.
After constructing large circle passing through all 6 holes, whatever the diameter is shown of constructed circle should not be changed. Construct immediately after you create all 6 holes that would avoid any problem of work plane changes.
No, that's wrong. The callout controls the relationship of the holes to each other (the pattern) as well as the pattern's relationship to datum A. See
NinjaBadger 's explanation in post number 11 which is almost correct (I'll explain in a full post rather than a comment so that I can include screenshots).
The only slight difference in interpretation to
NinjaBadger 's explanation comes from the fact that there is no Ø symbol preceding the positional tolerance - as was pointed out by
Matthew D. Hoedeman in comment 5.2. With no Ø symbol, the tolerance becomes a planar zone and, since only the 60° angular relationship between each hole is a boxed dimension (the BCD isn't), then you should set the zone orientation control in the Geometric Tolerance command to "right angle to radial" I've simulated this using the Hexagon training block and included a screenshot of the graphics window showing the tolerance zone's.
The Ø4 BCD is controlled separately and can be reported as a circle, constructed through the centroids of the 6 holes as
Jignesh was describing. You would just report it using a location dimension of the diameter to whatever the ± tolerances are (they're not shown on the original poster's screenshot).
However if it were me I'd seek clarification whether this is simply an omission/mistake on the part of the designer. I can't think of a functional reason why they'd want to control bolt hole position (with MMC) in an angular way but not radially.
