×
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!
  • Students Click Here

*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.

Students Click Here

Jobs

True position without diamter

True position without diamter

True position without diamter

(OP)
There is some disagreement among engineers at my work in the calculation of true position without a diameter call-out.  Given an open ended datum notch with the following tolerances:
Width .100 +/-.002
Drop from base of slot to datum surface is 1.267+/-.005
[TRUE POSITION|.006|E|F] (with basic dimensioning to datum points on datums E & F)

When calculating the true position without a diametric symbol is it necessary to double the positional measurement?

ie.  if the position checks .0084 from nominal is this a true position of .0084 (.0024 O/T), or is it a true position of .0168 (.0108 O/T)?

Jeanne

RE: True position without diamter

The diameter symbol or lack of a diameter symbol merely indicates the shape of the tolerance zone: whether it's 360º or not.  Your callout yields a tolerance zone of two parallel planes .006 apart, and centered around the perfect location.

Thus, the feature in question can only be .003 from nominal, in either direction.  That's where the .006 comes from.

If a diameter symbol were included, then it would be allowed .003 from nominal, in any radial direction (.006 total diameter tolerance).  Of course for your situation the diameter wouldn't make sense. But the numbers work the same, only the shape is different.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

RE: True position without diamter

(OP)
Your explanation makes complete sense.  Thank you for your help.  I couldn't quite figure out from ASME GD&T why there was sometimes a diameter call-out and other times not.

Jeanne

RE: True position without diamter

A diametrical tolerance zone should only be used on features of size that are round and not on slots or rectangular notches. How many times have I seen a DTZ on a slot? Quite a few but it is not applicable since one would lose orientation.  

Dave D.
www.qmsi.ca

RE: True position without diamter

Quite right, Dave.  Time to slap the knuckles of those designers.

Jim Sykes, P.Eng, GDTP-S
Profile Services  www.profileservices.ca
TecEase, Inc.  www.tec-ease.com

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