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Hole perpendicularity

Hole perpendicularity

Hole perpendicularity

Hi All,

I got a file generated from a CMM machine for measuring some par maters of drilled holes such as circularity and hole size, I also found that it measured perpendicularity (it shows PERP) so I assumed it is perpendicularity. my question is what is the unit usually used for measuring hole perpendicularity. is it mm or degrees. I am just not sure which one is used for drilled holes. also is there a book or a video where it shows how perpendicularity is measured using a CMM machine.


RE: Hole perpendicularity

Perpendicularity is defined in degrees and is the angle of the hole axis relative to the part surface; in most cases it should be 90 degrees. The drawing or hole drilling specification should define the acceptable tolerance from perpendicular. An excessive hole angle from perpendicular will result in improper fastener installation, clamp-up, seating, etc and reduced joint strength.

RE: Hole perpendicularity

As the name implies, a CMM records the coordinates of discrete points on the part surface being inspected. The CMM only measures surface point coordinates. Software is used to calculate every other geometric condition based on these surface point coordinate data measurements. With conventional GD&T practice such as ASME Y14.5, the perpendicularity tolerance defines a theoretical boundary the controlled feature must lie within, and the tolerance limits are linear values (mm or inches) rather than angular values (degrees or radians).

Check with your inspector to determine what units were used in the report and what standard the inspection was performed to. Then get a copy of the GD&T standard and give it a read.

Good luck to you.

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