INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Jobs

End Bell ( End Shield ) with shaft extension....GTOL callout

End Bell ( End Shield ) with shaft extension....GTOL callout

(OP)
to all,

I have an motor assembly with and End Shield machining customer rabbet with a shaft extension thru the end shield.
The A datum in the shaft extension diameter, and datum B is the customer machined diameter bottom surface.

Someone put a GTOL of | position | .006 | A | B |

I want to change it to | concentricity | .006 | A |

Is this an accurate GTOL to change to ?

Thanks
Mark

RE: End Bell ( End Shield ) with shaft extension....GTOL callout

I don't know why you'd want to change it at all, honestly. It's effectively identical unless I'm mistaken.

I've seen comments on this forum from "people who would know" that concentricity may be going away in future ASME Y14.5 revisions (assuming that's what's in play here) because it's, iirc, considered redundant.

It's quite difficult for me to make out some of the details of your screenshot due to it being shrunk down, so I apologize if I've missed something key.

Edit-to-add - if I would change anything, I'd remove Datum A from the 1/2-20 feature and put it on the precision diameter of the shaft's more-critical centerline.

RE: End Bell ( End Shield ) with shaft extension....GTOL callout

Concentricity is the axis related equivalent to planar related symmetry, so it is not the same as position.

In the A|B reference frame, B controls no additional frame of reference refinement as A has already taken the same degrees of freedom. The B|A Reference frame would typically make more sense.

RE: End Bell ( End Shield ) with shaft extension....GTOL callout

I see a significant difference in the datums.

The first method is wrong, because B adds no refinement to A when A is primary.

The second method is weak because you've cut away more than half of -A-. For the machinist this is not a big deal but for an inspection now A has become short in length and a weak datum.

The best method IMHO is to fix the first method. Put B as primary and A as secondary. This makes B drive the vector direction and lets A contribute only a point.

One last point of note: B is probably not the mating surface. The mating surface on this kind of motor is surface surrounding the bolt holes. B surface usually does not touch anything.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close