Checking Dimensions of a Half disk

Hi,

I am machining cylinders into disks and then cutting these disks in half to create half disks. Unfortunately it appears that some of the bottoms of the half disks are not parallel to the tangent of the arc of the disk which is crucial to what I am doing. I have little experience with checking dimensions and would like to know if anyone has any input on how to check and see if the tangent to the arc is parallel to the bottom and if it isn't how much it is off by and then how to mark the sample so that I can fix it in a surface grinder. I appreciate any help. Thanks.

I am having a bit of a problem understanding your issue; but, any absolutly straight cut that passes through the true center of the disc should produce a geometrically accurate semicircular disc.

As a result, measuring the height from the bottom to the top of the half disc to verify that the bottom face passes through the true center of the disc and verifying the strightness of the bottom is all that should be required to verify a geometrically and dimentionally accurate finished part.

I assume you are not trying to get two "half" discs from each full disc because only one geometrically correct half disc with the bottom face passing through the true disc centerline can be attained from each machined full disc.