Perpendicularity Length measurement

[rayhawk]

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?

 

[Belanger]

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

 

[rayhawk]

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.

 

[MechNorth]

Good explanation, JP.

Jim Sykes, P.Eng, GDTP-S
Profile Services

http://www.profileservices.ca

TecEase, Inc.

http://www.tec-ease.com

 

[KENAT]

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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(probably not aimed specifically at you)
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[MechNorth]

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

http://www.profileservices.ca

TecEase, Inc.

http://www.tec-ease.com