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Perpendicularity Length measurement

Perpendicularity Length measurement

Perpendicularity Length measurement

(OP)
Hi guys, I am using a Mitutoyo QM-Data200 2D data processing unit on a horizontal projector to measure parts. When I go to measure perpendicularity between two features, the machine requires me to input a length value. I assume this length is the length of the feature I am checking the perpendicularity of, but it seems odd to me that they would ask something that the machine should be able to easily calculate.  I have gone through the user manual, and it does not address perpendicularity measurement. From what I can find in the ASME Y14.5-1994 spec, no length is required when measuring perpendicularity, so why does the machine want a length value here?   

RE: Perpendicularity Length measurement

When checking perpendicularity, the tolerance value is always given in linear units.  At first it might sound funny to be measuring an angle to a tolerance in mm or inches, but think of that tolerance as a bandwidth.  Over the length of that surface, the surface may not tilt outside of that bandwidth.

So that's probably why it needs to know the length.  I don't know enough about the inspection machine to say why it can't figure it out for itself if that feature has already been measured for length.

John-Paul Belanger
Certified Sr. GD&T Professional
http://www.gdtseminars.com

RE: Perpendicularity Length measurement

(OP)
So then would you say I should put in the length of the feature I am checking the perpendicularity on?  That seems like a fair assumption to me, but I was hoping somebody else might be familiar with this type of machine.

RE: Perpendicularity Length measurement

Well, a bit of a week answer but some tolerances can be specified over a unit length if memory serves, maybe it's to allow that?  I can't recall if perpendicularity is one of them though.

However I'd have thought even if that's the reason, it's default should be the feature length.

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RE: Perpendicularity Length measurement

Flatness & straightness are allowed on a per unit length basis to ensure that there are no sudden transitions.  There's no support for per-unit-length specification of orientation controls in the standards ('94 or '09), and you could still use flatness or straightness per unit length as a refinement of other controls.

Jim Sykes, P.Eng, GDTP-S
Profile Services  www.profileservices.ca
TecEase, Inc.  www.tec-ease.com

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