×
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

# Flatness call-out

 Forum Search FAQs Links MVPs

## Flatness call-out

(OP)
I have a question about a  Flatness feature control frame on a part drawing.
The surface machined surface is approx 300MM x 700MM
Profile 0.75 X
Profile 0.5 - freestate
Flatness 0.1/ 75 x75
Max overlap 3MM
Min overlap 1MM

I'm good with most of it but Ive never seen the 75 x75 called out .....Does it mean I only measure flatness in section 75 x 75 (using the max/min overlap as my tolerance)and not the entire surface. This would seem to make sense  otherwise the profile 0.5 freestate  call out would be pointless. Am I right????

Thanks for any help, Randy

### RE: Flatness call-out

Tizbass,

Flatness 0.1/75x75 means that every 75x75 square portion of the surface has to be inside tolerance zone, that is two parallel planes 0.1 apart.
I think profile in free state condition has nothing to do with the flatness, unless flatness is also specified in free state.

### RE: Flatness call-out

The 75 x 75 is a per-unit area requirement.  It's in '94 in 6.4.2.1.1

It means that in any and every area of 75x75mm, the local flatness cannot exceed 0.1, with the workpiece restrained as specified.  The min & max overlap is an interesting twist that I've not seen before; it means that there are discrete regions to be checked.  Typically, the entire surface would be checked and any area where there is a sudden transition would be marked off & rechecked within a floating 75x75 area (i.e. a mylar cutout that you move around).  The indicated overlap would actually allow a restrained flatness of 0.97 overall, which exceeds the freestate flatness.  That isn't good.

As shown in the cited section, there's usually a composite feature control frame with an overall flatness callout on the top and a per-unit refinement underneath.

The profile 0.5 - freestate, without any datum reference, gives you freestate flatness on the feature.  Not sure what the Profile 0.75X is about.  A graphic would help.

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

### RE: Flatness call-out

The profile is overall on the feature and is relative to at least one datum while the flatness cannot be over 0.1 mm in each 75X75 mm zone and is independent of the profile.

Flatness shown in this manner controls rapid change in the surface. If one had a flatness of 0.3, as an example, we could have it all in one area so the 75X75 zone controls rapid changes in the surface.

Hope this helps.

Dave D.
www.qmsi.ca

### RE: Flatness call-out

(OP)
Yes it does help...Thanks. We were trying to hold a flatness of 0.1 over the entire surface which I don't think we needed to do.

#### 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!

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:

• Talk To Other Members
• Notification Of Responses To Questions
• Favorite Forums One Click Access
• Keyword Search Of All Posts, And More...

Register now while it's still free!

Already a member? Close this window and log in.