×
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

Flatness and parallelism

Flatness and parallelism

Flatness and parallelism

(OP)
Looking some of our old drawings I keep seeing surfaces with a parellel requirement along with a flatnessness requirement of the same magnitude.

I was under the impression that parallelism already requires flatness to within the parallelism requirement, majking an additional flatness requirement (equal or greater to the parallelism) completely meaningless.

I did search for this but I didn't find anything (that I agreed with) that adresses this exact question.


from y14.5 Sec 6.3.3:
"Parallelism is the condition of a surface or feature's
center plane, equidistant at all points from a datum plane;
or a feature's axis, equidistant along its length from one
or more datum planes or datum axis."

A datum plane is perectly flat so I don't see how this doesn't require flatness.

RE: Flatness and parallelism

If the flatness control is not a refinement of other geometric tolerances that control the flatness of the surface then it is an "illegal" specification.  

Perpendicularity, Parallelism, Angularity, Total Runout and Profile of a Surface are all controls which can control the flatness of a surface so if one of those has the same effect as the flatness then the flatness is redundant and should be removed.

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

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.
 

RE: Flatness and parallelism


Out of curiosity - how old are "old" drawings?

Also, are there any additional symbols / requirements ("free state", "per unit"), etc.?
 

RE: Flatness and parallelism

Also the standard question, what standard is invoked on the drawing?  ISO treats things differently than ASME does.   

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

RE: Flatness and parallelism

I think both ISO and ASME see parallelism as controlling flatness.   (The relationship between size and flatness would be different in ISO.)
 

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

RE: Flatness and parallelism

... old, however can be a relative term.

"Good to know you got shoes to wear when you find the floor." - Robert Hunter
 

RE: Flatness and parallelism


I am completely making it up, but imagine this hypothetical situation:
Flexible part;  Flatness is called "per unit" to make sure surface is smooth. However Parallelism can only be achieved in Restrained state, so in a sense Flatness IS refinement.

Also from "never say "never"" department.
Per Y14.5-2009 Parallelism may be called with "tangent" requirement, which allows for surface to "cave-in".  In this case Parallelism DOES NOT control Flatness.
Since somebody asked for this, could it be the 70-s or 60-s version of the standard had similar clause?
 

RE: Flatness and parallelism

(OP)
Well the original drawings are from the 70s, they were updated at some point but no one really put any thought into the GD&T.  These specifically call out Y14.7 (97) and the flatness I am referring to is total.

Thanks for the feedback, it seems I came to the right place.

RE: Flatness and parallelism

(OP)
where in Y14.5 is the discussion of the tangent modifier?

RE: Flatness and parallelism

It's paragraph 6.6.1.3 of the 1994 edition, or paragraph 6.5 of the 2009 edition.

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

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