Re: Capability study on true position callout. What would be the upper and lower spe
True Position as is all form tolerances are 99.9 % of the time unilateral, so you would only have a upper limit. The only time that I can think of where they may be a bi-lateral tolerance would be for callouts like .00002" - .0001" Flatness, I measure parts with this tolerance and it is bi-lateral. There are probably others but they are not the norm.
Like previoiusly stated, make sure the software or excel form you are using will calculate unilateral tolerances and you enter this information correctly (either enter a zero or leave the lower tolerance blank; on the form I use, you actually have to specify if it is a bilateral or unilateral tolerance and if you indicate unilateral it automatically blanks out the box for the lower limit). What type of gage are you using to check position, a fixture (attribute gage) or something like a CMM (variable gage)? In the positional dimensions that I inspect, I use a CMM. I am able to either enter the calculated position or I can use the X,Y & Z coordinate values it reports. The coordinate values are much more accurate, they tell the exact location, whereas the calculated positional value basically tells you what zone you are in, but because your zone is a circle you do not know exactly where you are at (EXAMPLE: .0002" position could be .0002" anywhere within that zone, whereas X=2.00 , Y= -.999 & Z=1.250 is an exact location.)
Thanks,