GD&T Related but more on Measuring technique question

[brandnew1]

Hi All,

This is a question more on measuring and wanted to get opinions on correct way to evaluate blueprint callout.

A small diameter is placed at the angle of 45° at the end of a diametrically shaped part. i have measured this on a CMM and found that the values to be with the +/-.010 tolerance, however when measured on a comparator the value doesn't come in as good.

My question is whether the comparator is an accurate method to measure as you are only viewing the surface of this hole and just measuring the distance of the hole created and determining the distance from the end compared to the CMM measuring the diameters inside the hole?

Also does anyone know what, "circumferential location optional" means?

thank you

 

[powerhound]

Both techniques have inherent measurement error potential. With the comparator, an accurate measurement is highly dependent on having the part correctly oriented. Other than that I would imagine that you'd get a pretty accurate measurement. The CMM is a whole different story. You can get a variety of different results depending on how you evaluate both the datum features and the toleranced features.

John Acosta, GDTP Senior Level
Manufacturing Engineering Tech

 

[Harpreet13]

Hi, I have seen drawings with circumference location optional but in those cases it was a round part i.e. machined pipe, there was a drain hole at a angle.
if that's the case then I believe it can be anywhere on the pipe circumference.

If I have to inspect this diameter looking at the tolerances, I would be simply checking it on shadow graph by inserting a pin in it. For the protractor & cmm I agree what powerhound said.