Parallelism

[Maxim87]

Hello all,

Please help understanding a parallelism of a hole. For example, we have a drawing as below:

In 3D view it can be represent like this:

https://files.engineering.com/getfile.aspx?folder=08d1e288-b109-4ed0-be32-fe3e69d0ede9&file=1.JPG

How I understand that if the axis of a hole is in the cylinder with diameter of 0.02, the piece is acceptable how it is represented in Picture 1.
But a question appear in my mind, how the zone the tolerance is oriented?. In my mind, it can be like Picture 2 (the axis of zone of tolerance is parallel with datum A), please correct if I am wrong.
Thanks a lot in advance for future answers

 

[3DDave]

Parallelism requires a reference to be parallel to. This doesn't have the required reference. This appears to be a mistaken use of the symbol and most likely should have been straightness. Whatever the intended control, the one that is there is not interpretable.

 

[ewh]

3DDave is correct; you need to reference the datum that the axis is supposed to be constrained to.
You are correct that it only controls parallelism of the axis relative to datum A.

"Know the rules well, so you can break them effectively."
-Dalai Lama XIV

 

[dgallup]

Parallelism, if properly applied, would only control relative to the planar datum, it could move all over the place in the other direction as you have shown. Normally you would use the position control if you want to control a hole relative to two datums.

----------------------------------------

The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.