×
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

Profile of a surface

Profile of a surface

Profile of a surface

(OP)
Hi all... I'm a GD&T newbie & here I have a simple yet silly question...

Suppose I have a block & let's say one of its sides says that it has a Profile of Surface tolerance as "1 mm"

In another case, having the datums conventionally defined (in both cases), it says it has a Profile of Surface tolerance as "1 mm" w.r.t (let's say) A|B|C

I wanna know this : 1. What is the difference in the profile tol. with & without DATUMS?
2. When to give datum reference & when not to?



RE: Profile of a surface

Quote (pratyu)

1. What is the difference in the profile tol. with & without DATUMS?
Have a look at attached picture:
http://files.engineering.com/getfile.aspx?folder=d...

This should help you to grasp the key difference. In general, profile without datum feature references does not control any relationship between controlled surface and datum(s). For simple surfaces, like shown in case #2 in the attachment, this means the profile is capable to control form of the surface only (flatness error in this particular case). The controlled surface can be at any angle relative to datum plane A and at any distance from A. For irregular features of size, like irregular holes or pins, if the true contour of the feature is defined with basic dimensions, profile will control size of the feature in addition to its form.

If profile feature control frame contains at least single datum feature reference, it controls more than just size and/or form. In case #1 in the attachment it controls location of the surface relative to datum plane A and in the same time parallelism of the surface to A (the profile tolerance zone is located from and oriented to datum plane A).


Quote (pratyu)

2. When to give datum reference & when not to?
If you are interested in controlling form and/or size of the feature without controlling its relationship to any datum(s), profile without datum feature references can be used. If more than that is needed, that is orientation and location control, datum feature references shall be specified.

RE: Profile of a surface

In that attachment, pmarc, I think you meant to remove the basic dim box around the height of 10 :)

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

RE: Profile of a surface

Well, actually I did not, J-P. I rather wanted to show that the basic dimension would have certain meaning in case #1, and would be meaningless in case #2.

RE: Profile of a surface

(OP)
pmarc,

Why don't we require basic dimension in the second case?

RE: Profile of a surface

Basic dimension is meaningless in case #2 because profile feature control frame is not controlling any relation between controlled surface and datum plane A (due to lack of datum feature A reference).

RE: Profile of a surface

(OP)
Okay!
In case 1, suppose I remove the basic dimension, and give the tolerance 10 +/- 1 mm, and the datum is referenced, & the actual height value is 10.05 mm, we have a profile tolerance zone of 1 mm at the height of 10.05 mm. Am I correct?

RE: Profile of a surface

Quote (pratyu)

In case 1, suppose I remove the basic dimension, and give the tolerance 10 +/- 1 mm, and the datum is referenced, & the actual height value is 10.05 mm, we have a profile tolerance zone of 1 mm at the height of 10.05 mm. Am I correct?

Well, not exactly. If dimension is directly toleranced, say 10 +/- 1 mm, profile tolerance 1 wrt A is free to float within 9 - 11 bandwidth, but it is not centered/located at any value.
If the actual height value (measured from datum plane A) is 10.05 everywhere, that means the actual profile of surface error is 0.

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