Hello all,
Measuring true position of a line is irrelevant. True position in simple term is used to only define location positioning for "feature of sizes". Most likely used referenced off of datums.
If you are trying to measure a position of a line, there are other GD&T that will offer as a great replacement. Sometimes Mechanical Engineers don't know how to apply GD&T to drawings...
Just gotta correct them.
Hello all,
Measuring true position of a line is irrelevant. True position in simple term is used to only define location positioning for "feature of sizes". Most likely used referenced off of datums.
If you are trying to measure a position of a line, there are other GD&T that will offer as a great replacement. Sometimes Mechanical Engineers don't know how to apply GD&T to drawings...
Just gotta correct them.
Thank you Billy very much for prompt response ! But, sorry, even in this case, we report the slot's center position ? its looks like I have to tolerance both arcs (measured 180 deeg) for orientation control as well? ..and.. Im just wondering, what is this replacement , you are mentioned, about position of a line ? thanks Yuri
Hey Yura,
There are other GD&T used to best define the quality control the engineers are aiming for. Usually these are chosen for best fit and function with the mating parts altogether. The basics Flatness, straightness, cylindricity, circularity are used to control form non related to other features. Perpendicularity, parallelism, and angularity are used to indicate orientation non related to other features. True position, profile of surface, and profile of a line is used to control location. Position controls based off center points, for location. It can control orientation depending on datum structure/alignment. Profile is used to control size, surface and form. Profile may be used to measure distance of line, form of that line, etc. There are a few more GD&T that may be addressed but as long as you read the ASME Y14.5 guide for GD&T you'll get a good whiff of it.
In order to control the rotation of the slot, either TP on the two radiis, TP on the width or have the slot controlled with profile. If the TP is evaluated to the center of the line (and not the entire length of the line) it is not being controlled it the way it is intended (rotation around it's center point). One-axis TP on the length and another on the width are common ways.
