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1-Newbie

## difference between circularity and circular runout

what is the difference between circularity and circular runout? and cylindrecity and total runout in tolerance?

do they use only axis as refence or any other reference?

shankar

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1 ACCEPTED SOLUTION

Accepted Solutions
1-Newbie
(To:ptc-4328935)

Hi

When you check circularity you are checking the variation in the circle with out considering any datum

But when you are checking the variation with reference to a datum then it is Circular runout

(Circular runout is the combination of Circularity and Coaxiality)

In simpler words when we fix the job axis and check the variation with dial gauge you check-Circular runout

But when you do not consider any datum then it is circularity

Let suppose a part at a section is having less deviation in circularity may have higher circular runout value if it is axially shifted from the datum

Regards

K.Mahanta

Message was edited by: kshetrabasi mahanta (image added)

10 REPLIES 10
1-Newbie
(To:ptc-4328935)

I would define it thus....

1. Take a cylinder / cone
2. Divide the cylinder / cone into number of sections

Circularity

At each section you would get a circle. Circularity is the VARIANCE of this circle from the THEORETICAL circle. Generally, 4 points are taken for measurement. These 4 points would give you 4C3 circles or 4 circles. An average of these FOUR circles is taken to define the deviation.

Cylindricity

1. While circularity is applicable for both Cone and Cylinder, Cylindricity is the VARIANCE of EACH of these circles obtained accross the length of the cylinder.

Runout

1. Runout is the measure of the deviation with respect to the AXIS. While runout is to ONE side, Total Runout or TIR is the TOTAL Runout as the part rotates by 360 deg or the total VARIATION seen on the Dial Gauge.
1-Newbie
(To:s.iyer)

Thanks.

understood to some extent. can anybody explain in more easier way to understand. i am a beginner, so i need little more explanation.

shankar

1-Newbie
(To:ptc-4328935)

Do a search for geometric tolerancing then go and do a course on it.

http://www.tec-ease.com

Its fundametal to mechanical engineering and is usually not taught at engineering schools. Some would say its a black art.

1-Newbie
(To:ptc-4328935)

Please study IS:8000 (parts I, II and III). You may also refer to CMTI handbook.

1-Newbie
(To:ptc-4328935)

Hi

When you check circularity you are checking the variation in the circle with out considering any datum

But when you are checking the variation with reference to a datum then it is Circular runout

(Circular runout is the combination of Circularity and Coaxiality)

In simpler words when we fix the job axis and check the variation with dial gauge you check-Circular runout

But when you do not consider any datum then it is circularity

Let suppose a part at a section is having less deviation in circularity may have higher circular runout value if it is axially shifted from the datum

Regards

K.Mahanta

Message was edited by: kshetrabasi mahanta (image added)

Hi Shankar,

If one of the responses helped resolve your issue, would you please mark it as the Correct Answer?  That way other users visiting the discussion will know; as the correct answer gets copied right below the question.

Thanks,

Amit

23-Emerald III
(To:AmitDeshpande)

Why are you reviving an almost 4 year old thread? Just curious.

Just doing some clean up to close out older discussions.

23-Emerald III
(To:AmitDeshpande)

If you look at Shankar's profile, he hasn't logged in since Dec of 2011. Do you think he is going answer?

shankar k

Emeritus
(To:Dale_Rosema)

Hi Dale,

As Amit wrote, we are clearing up some older discussions and you are right, Shankar may not respond; best practice is the Original Poster marking an answer correct - I am sure Amit simply did not note his log in

Best,

Toby

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