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Compound Angles 101 (#281)

(In accordance with the ASME Y14.5-2009 standard)

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Often the placement of dimensions can cause folks down stream to make a lot of unnecessary calculations.  It is very common to use linear dimensions to locate a point at one end of a hole.  This point is where the theoretical axis of the hole pierces the perfect plane at one end of the hole.  The problem is that on the actual part, you will not know where the theoretical point is.  On this first drawing, three coordinate dimensions locate a point in space.  From that point the axis of the hole goes off at a compound angle.  Good luck finding that point on the actual part.

A better technique is to dimension from the 0,0,0 origin of the datum reference frame to the axis of the hole.  The position tolerance applies to the hole axis.  Inspection needs to measure deviation of the actual hole axis from the basic location.

On this second drawing two auxiliary views have been drawn in order to view the true size of the two holes.  In the second auxiliary view you are looking down the axis of the two holes.  Dimensions start from the 0,0,0 origin of the datum reference frame to the axis of each hole.  The deviations of the actual axis of each hole may be measured in order to determine if the holes are within the stated position tolerance.

The drawings are intentionally incomplete.

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Back to Tips Tip added Jun 2013