Design and Engineering Forum Forum Moderators: randykimball, Administrator | POSTING POLICY / RULES | How to post an Image
 Geometric tolerance: Circularity and Circular runout Post Reply Engineering Forum
 Posted by: Harsimran ® 02/04/2009, 07:31:40 Author Profile eMail author Edit Hi GDT expertsHow do I measure Circularity and Circular runout tolerances in my tool room , I dont have a CMM, but I have a Granite surface and blocks and nearly all measuring instruments. The part in question is a simple one . Its a shaft with one step in diameter. Larger dia is 50mm and 100mm long, smaller dia is 25mm and 25mm long. Circularity on smaller dia is .13 and circular runout on smaller dia wrt to larger (as datum) is also say .13 This is a hypothetical part.Thanks Harsimran

 Replies to this message

 : Geometric tolerance: Circularity and Circular runout : Geometric tolerance: Circularity and Circular runout -- Harsimran Post Reply Top of thread Engineering Forum
 Posted by: traingdt ® 02/04/2009, 09:15:47 Author Profile eMail author Edit Circularity is one of the hardest geometric tolerances to check, because it is tolerancing the shape of the part separated from all other qualities like size, position, etc. Therefore, using traditional gage tools always comes up short. (For instance, if you use a micrometer, that only gives you the distance across two points; the part could be an octagon and the micrometer won't know that.)The best way to check circularity is with a CMM or with a special machine dedicated to circularity called a roundness machine. You're limited to traditional tools, so I suppose you could implement a couple of methods simultaneously, and using a composite of the different results, it can be determined to some degree if the circularity is correct.But, here's the easy answer: since your hypothetical example has circular runout and circularity on the same feature (both to .13), you can easily check the circular runout, and the circularity is automatically verified!To check circular runout, mount the part on datum feature A -- use a chuck or collet to hold the large diameter. Then rotate the part. As it rotates, have a dial indicator mounted such that it rides the surface of the small diameter, at any randomly selected cross-section, over one revolution. The needle shall not deflect more than 0.13 from its highest to lowest reading during that revolution. Then move the dial indicator over a little, and repeat the check. (How many cross-sections to verify is not prescribed -- it's a judgement call depending on the material of the part and its length; but do as many as practical).Hope that helps! Modified by traingdt at Wed, Feb 04, 2009, 09:18:02

 : : Geometric tolerance: Circularity and Circular runout : : Geometric tolerance: Circularity and Circular runout -- traingdt Post Reply Top of thread Engineering Forum

 : : Geometric tolerance: Circularity and Circular runout : : Geometric tolerance: Circularity and Circular runout -- traingdt Post Reply Top of thread Engineering Forum
 Posted by: Harsimran ® 02/05/2009, 09:05:05 Author Profile eMail author Edit Thanks a lot, I never came across en engineering forum so quick and exact on the answers. Kelly, your team is doing a great job !!!!!and u too.......I am sure to bombard you with more questions........

 : : : Geometric tolerance: Circularity and Circular runout : : : Geometric tolerance: Circularity and Circular runout -- Harsimran Post Reply Top of thread Engineering Forum
 Posted by: randykimball ® 02/10/2009, 09:44:45 Author Profile eMail author Edit Rotate the part in VEE blocks with indicators at the horizontal and vertical positions. This will show run out and out of round. The worst suggestion of your lifetime may be the catalyst to the grandest idea of the century, never let suggestions go unsaid nor fail to listen to them.