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Hello! No doubt somebody has posted something similar on this forum at some time or another, but I sure can't find it. I am hoping that I can get a definitive answer here because I seem to find myself stuck between two opinions that both make sense to me.
I have attached a sketch that depicts an assembly of two tubes attached to each other at the end, each with a bracket. the surface of one of the brackets is datum A and the hole in the same bracket is datum B. There is no other datum shown on the drawing, but there is a dotted line going through the center of the attached tubes. There is a true position callout on the hole of the second bracket and a basic dimension showing the distance between the holes, but not the distance from the centerline of the tube to the holes. The hole that is -B- is referenced, but not the hole we are checking(which is also 70). Size and location of both holes are fully drawn out and controlled on sub-assembly drawings.
So, my dilemma: The guys in the met lab say that the dotted line is an assumed datum, so the part is set up on plane -A-, aligned with the tube center line and true position is calculated using data derived from both the X (200) and Y (70). My design engineer says, nope, the Y(70) is controlled at the sub-assembly level, hence no basic dimension for this on the drawing. This is a straight line true position. Set up the part on datum A, call B zero and measure the shortest distance to the hole in the 2nd bracket.
Based on the function of the part, I agree with the design engineers intent, but I am really not sure if he drew it correctly or I need to request a drawing change. Either way, I am going to have to fully understand it myself in order to explain it to one of them. And if I do need a drawing change, what would best fit the intent?
Thank you so much! (boy, I hope the guys in the met lab are not reading this!)
I have attached a sketch that depicts an assembly of two tubes attached to each other at the end, each with a bracket. the surface of one of the brackets is datum A and the hole in the same bracket is datum B. There is no other datum shown on the drawing, but there is a dotted line going through the center of the attached tubes. There is a true position callout on the hole of the second bracket and a basic dimension showing the distance between the holes, but not the distance from the centerline of the tube to the holes. The hole that is -B- is referenced, but not the hole we are checking(which is also 70). Size and location of both holes are fully drawn out and controlled on sub-assembly drawings.
So, my dilemma: The guys in the met lab say that the dotted line is an assumed datum, so the part is set up on plane -A-, aligned with the tube center line and true position is calculated using data derived from both the X (200) and Y (70). My design engineer says, nope, the Y(70) is controlled at the sub-assembly level, hence no basic dimension for this on the drawing. This is a straight line true position. Set up the part on datum A, call B zero and measure the shortest distance to the hole in the 2nd bracket.
Based on the function of the part, I agree with the design engineers intent, but I am really not sure if he drew it correctly or I need to request a drawing change. Either way, I am going to have to fully understand it myself in order to explain it to one of them. And if I do need a drawing change, what would best fit the intent?
Thank you so much! (boy, I hope the guys in the met lab are not reading this!)