We have a job on now, it's a housing with an internal cylinder as the only datum on the drawing. I need to check the perpendicularity of all the machined faces to this cylinder, also all the other bores for concentricity.

I measured the cylinder using 8 points, I measured two rows of four with the second row twisted 45 degrees for an even spread. I levelled it in Z, then set it as the origin in X and Y. I measured a plane further up on the part and set this as the origin in Z.

When I check for concentricity, I get completely random dimensions, ranging from 0.35 to 1.45! Also the perpendiculrity od the planes to the cylinder is way out, I have checked it on a height gauge.

Am i doing something wrong here? Is there a better way of measuring the cylinder and setting it as the datum? We took a part over to the customer and they checked it on their zeiss machine, and embarrassingly for me, it came out consistently correct...

I measured the cylinder using 8 points, I measured two rows of four with the second row twisted 45 degrees for an even spread. I levelled it in Z, then set it as the origin in X and Y. I measured a plane further up on the part and set this as the origin in Z.

When I check for concentricity, I get completely random dimensions, ranging from 0.35 to 1.45! Also the perpendiculrity od the planes to the cylinder is way out, I have checked it on a height gauge.

Am i doing something wrong here? Is there a better way of measuring the cylinder and setting it as the datum? We took a part over to the customer and they checked it on their zeiss machine, and embarrassingly for me, it came out consistently correct...

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