×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Are you an
Engineering professional?
Join Eng-Tips Forums!
• Talk With Other Members
• Be Notified Of Responses
• Keyword Search
Favorite Forums
• Automated Signatures
• Best Of All, It's Free!

*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.

# Definition of Ovality?

## Definition of Ovality?

(OP)
How would you define ovality?

One definition is 2*(D-d)/(D+d).  Another example I came upon is D=18.74, d=18.53, Ovality=0.19, which does not correspond to the above formula.

Thank-you.

### RE: Definition of Ovality?

You might also search for "eccentricity".  I'm not sure how it's calculated (maybe like your second example?), but it measures how "elliptical" a round figure is.  I believe the method behind it is that all circles look like ellipses when viewed from an angle.  Therefore looking directly down on a true circle would give an eccentricity of 1, and looking at the side of a circle would give an eccentricity of 0 (a straight line segment).

### RE: Definition of Ovality?

(OP)
Thanks for your insight, however I don't know how the second example was calculated. The diameter difference is 0.21, not 0.19.

### RE: Definition of Ovality?

(OP)
I believe my first definition is a weighted average whereas the second description was an attempt at expressing ovality as the difference between major and minor diameters.  I have not come across ovality expressed as a geometric tolerance and was wondering why runout would not do.  For instance pistons are machined using ovality tolerances:   major diameter minus (somethingA) +/- (somethingB).  To my surprise pistons are machined as ovals, (how this is done, I would appreciate if someone could comment). This is so that differing thermal expansions of the piston mass can assist in sealing. In general a piston's cross-section is different at right angles due to the wrist-pin. And, an oval is basically an ellipse, or a circle with all the runout at 90 degrees.  Any comments would be appreciated.

### RE: Definition of Ovality?

What I was thinking is something more along the lines of: (D-d)/D

The result would be between (0,1).  My last post reversed the numbers, so 0 would be a perfect circle and 1 would be a line segment.

#### 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.

#### Resources

Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a partâ€™s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now

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!