Smart questions
Smart answers
Smart people
Join Eng-Tips Forums

Member Login

Remember Me
Forgot Password?
Join Us!

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips now!
  • 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!

Join Eng-Tips
*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 from Indeed

Link To This Forum!

Partner Button
Add Stickiness To Your Site By Linking To This Professionally Managed Technical Forum.
Just copy and paste the
code below into your site.

BiPolarMoment (Mechanical) (OP)
21 Dec 11 10:25
This is a simple question that I'm embarrassed I can't find an answer for. Given a simple hole in a part where I'm interested in more tightly controlling deviation in the 'x' direction than the 'y' direction can I simply do a single segment position tolerance where the first segment one establishes overall deviation in the x-y plane and then a tighter tolerance while omitting the datum corresponding to y?

e.g. ( Datum corresponds to a normal plane of the same direction)
| Pos | Dia .010 | X | Y | Z |
| Pos | .004 | X | Z |

Alternatively, is it permissible to establish the X and Y seperately (effectively creating a linear X/Y tolerance) e.g.
| Pos | .010 | Y | Z |
| Pos | .004 | X | Z |

I can't seem to find references to single segment or composite tolerancing when it relates to a single feature. Linear tolerancing isn't desired as the location is on two centerlines.

KENAT (Mechanical)
21 Dec 11 10:55
You could look at bidirectional positional tolerancing of features (section 5.9 of ASME Y14.5M-1994 7 fig 5-41 if that's the standard you work to).

This will give you a rectangular zone when arguably function by justify an obround zone but I'll leave that up to you to consider.

Posting guidelines FAQ731-376: Forum Policies (probably not aimed specifically at you)
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?

Belanger (Automotive)
21 Dec 11 11:13
Yeah... bidirectional is what you want (I can provide a picture if you don't have a GD&T reference book handy).  The two-single-segment examples you give aren't the best because the datums are being jumbled around. Think of a physical gaging scenario: the inspector would then have to jiggle the part against different edges for each positional check.  That's not what you want; you want him to set the part in a fixture only once, but then measure it in two directions to two tolerances.

IOW, the datum references given in the positional tolerance don't have to correspond on a one-to-one basis with the tolerance you are after.  They merely tell everyone how to hold the part.

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

BiPolarMoment (Mechanical) (OP)
21 Dec 11 14:18
Thanks John, I completely let that portion of the meaning slip my mind.  

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!

Back To Forum

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