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# perpendicularity question

## perpendicularity question

(OP)
hello - I was told today that I did not understand the use of perpendicularity - I have a piece that has 2 90 degree surfaces - the top surface is 10" long which is perpendicular to the front surface which is 36" long = the front surface is datum a the top surface is perpendicular to a within .001" - I was told that in this configuration that surface a could be out by at least .036" (.001"x36) - this does not seem right to me - I thought that surface b must lie between 2 planes within .001" perpendicular to surface a - I would think that if a straightness tolerance of say .001"per inch on datum a then that might apply - I just need to clarify it for myself - any help would be greatly appreciated - thank you

### RE: perpendicularity question

Certified Sr. GD&T Professional

### RE: perpendicularity question

(OP)
hello again |& thank you -

### RE: perpendicularity question

File cannot be opened. Try again with no special characters in file name.

Certified Sr. GD&T Professional

### RE: perpendicularity question

duk748,

As per ASME Y14.5, perpendicularity is a linear measurement, as you have described. Perhaps your co-worker thinks it is an angle.

--
JHG

### RE: perpendicularity question

duk748

Your interpretation is correct. There is no ratio "multiplier" based on the length of the datum feature or the feature under control. See Figure 6-3 on page 100 in Y14,5-2009. Note too, when applied to a planar surface, there is implied flatness equal to the perpendicularity tolerance.

Certified Sr. GD&T Professional

### RE: perpendicularity question

(OP)
hello again & thank you very much - i was sure i was right but considering his position i have to make it wrong - if you understand my meaning - thank you again for the vote of confidence - have a great day

### RE: perpendicularity question

Certified Sr. GD&T Professional

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