Correct Tolerance callout

[mromano1988]

I work for a company that makes these parts that were designed in the early 50's. So when looking at the prints There is not a datum structure defined nor any GD&T established. I have attached a picture of a mock part that we make. Its a casting that gets the I.D. turned on that lathe and then the part is taken to the mill where its sat on a fixture that locates the part on the I.D. then two holes are drilled and bored through the center of the part. Now in a perfect world the centerline of the two holes drilled and bored would intersect the centerline of the I.D. of the part. What kind of GD&T callout would that be. In my opinion its a true position call out(centerline of the two holes in relation with the centerline of the I.D. I work with a guy that keeps telling me its TIR. Well in my opinion TIR would be is you installed a shaft through the holes and checked the runout on that shaft. That would be TIR. But centerline position should be called out by a true position. Please let me know what you think. Thanksexample small.jpg

[Kelly_Bramble]

Specify the turned ID as Datum A, identify to one of the holes 2X size +/- tol. then a feature control frame | position | dia. tol_h | A |

This will control the axis of the two holes to tol_h accuracy. tol_h is equal to a diameter thus tol_h /2 = +/- some specified tolerance.

TIR is a surface displacement to axis control

[mromano1988]

Kelly, Thanks for the reply! Ok so TIR has nothing to do with the centerline of the two holes intersecting the centerline of the i.d. of the part?

[Kelly_Bramble]

Kelly, Thanks for the reply! Ok so TIR has nothing to do with the centerline of the two holes intersecting the centerline of the i.d. of the part?

For clarity - not useful for hole center lines perpendicular to each other.

[mromano1988]

Thanks!

[terry_williams]

I have a question and I hope someone can help me. I have around part that has a hole drilled in the center line of the "applied" centerline of the part. I have a "Y" dim of 2.50 +/- .030. I do not have a "Y" dim specified other that it shows it to be on centerline of the part.
What would my tolerance be for the hole location in "Y"?

[Kelly_Bramble]

I have a question and I hope someone can help me. I have around part that has a hole drilled in the center line of the "applied" centerline of the part. I have a "Y" dim of 2.50 +/- .030. I do not have a "Y" dim specified other that it shows it to be on centerline of the part.
What would my tolerance be for the hole location in "Y"?

Is there a default tolerance specified? +/- XXX, etc.