Number of inspection places for width callout

[lmd31]

I have a fairly simple callout for the width of a glass sheet (319.173 +/- 0.5 mm, one edge parallel to opposite edge within 0.3 mm). I am wondering if there is a minimum number of locations that the width needs to be measured. Are they required to run a probe down the whole edge and report the max and min? Is there a minimum number of locations to measure parallelism? If the edge is curved (i.e. the corners are even, but it bows in at the middle), would it still be called parallel? Is the parallelism "best fit edge" created by finding the high points on the edge (taking a plate and resting it on the edge, essentially) or is it created by some kind of weighted average of a bunch of points?

Whew, lots of questions. Thanks in advance for any responses.

Laura

 

[KENAT]

What drawing standards are you working to, ASME Y14.5M-1994? There've been a few posts about parallelism lately and on one of them I put some information from 14.5.

thread1103-217299 was most recent, there was one a few months ago where I put more from the standard but I haven't been able to relocate it recently, may have got wiped for copyright reasons.

KENAT, probably the least qualified checker you'll ever meet...

 

[ringman]

Typically the final verification of the part will be the responsibility of the inspection department. The standard establishes the parameters for geometry, but does not dictate the inspection methods to be applied.

This should apply to any/most drawing standards.

 

[axym]

Here are some quick answers and then a bit of explanation:

I have a fairly simple callout for the width of a glass sheet (319.173 +/- 0.5 mm, one edge parallel to opposite edge within 0.3 mm).
I am wondering if there is a minimum number of locations that the width needs to be measured. No

Are they required to run a probe down the whole edge and report the max and min? No

Is there a minimum number of locations to measure parallelism? No

If the edge is curved (i.e. the corners are even, but it bows in at the middle), would it still be called parallel? Possibly

Is the parallelism "best fit edge" created by finding the high points on the edge (taking a plate and resting it on the edge, essentially) or is it created by some kind of weighted average of a bunch of points? Neither

The parallelism requirement is that all points on the toleranced edge must lie within a zone 0.3 mm thick. That zone is defined to be parallel to the "true geometric counterpart" of the datum edge, physically represented by a surface plate resting on the datum edge.

Strictly speaking, the requirement is that all points lie within the tolerance zone. The method used to verify this, and the number of points sampled, is up to the inspector.

Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca

 

[lmd31]

So if I want to require them to measure more than one location for width and parallelism, I need to create a note to say so?

Thanks a lot for the quick answers, it helps.

 

[KENAT]

You don't normally put dimensional inspection requirements on the drawing. (Reference to statistical tolerancing is a partial exception I suppose.)

This is normally part of the quality plan or something, which may contain an annotated/marked up drawing.

KENAT, probably the least qualified checker you'll ever meet...

 

[fcsuper]

Yeah, it is more along the lines of putting it into work instructions.

Matt Lorono
CAD Engineer/ECN Analyst
Silicon Valley, CA
Lorono's SolidWorks Resources
Co-moderator of Solidworks Yahoo! Group
and Mechnical.Engineering Yahoo! Group

 

[MadMango]

If you add a Straightness callout to one edge in addition to your Parallelism, I would hope the Inspector would at least measure both ends and the middle of the opposite side, but there is no guarantee.

There's always inspection fixtures...

"Art without engineering is dreaming; Engineering without art is calculating."

Have you read faq731-376 to make the best use of Eng-Tips Forums?

 

[ringman]

Just curious, but could you explain a little more about the function of the glass and some info on how it is made.

 

[lmd31]

I can't give you details, but it's a flat, thin piece of float glass that is being die cut to shape. The question was really more theoretical, and could apply to any part though.

 

[KENAT]

To expound on what I put before with the drawing you're defining what you want. You don't generally specify how it's achieved (except when this overlaps with ensuring funcion - see ASME Y14.5 section 1.4e) or how it's verified.

KENAT, probably the least qualified checker you'll ever meet...

 

[vc66]

If you want them to measure at more than one place, then I would suggest a profile of surface callout on your parallel surface.

V

 

[ringman]

After some more thought, and after your feedback, I believe that the best approach would be to specify profile of a surface with the 'flat face' of the glass as primary datum feature.

The reason for that is that a 'narrow edge' as in your case does not lend itsself well to a datum feature. I realize you did nost specify the thickness, but my assumption is 1/8 - 1/4 in. or so.

 

[axym]

vc66,

I'm curious. How does the use of profile of a surface imply that they would measure at more than one place? Or that the original size and parallelism callouts would only be measured at one place?

Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca

 

[vc66]

axym-

It doesn't--directly. But any inspection of profile of surface that I've ever seen has the inspector running an indicator down the surface in question more than once to get a reliable reading. This is common sense--not necessarily standard, however. Parallelism seems to be more of a lax requirement than profile of surface in the eyes of the inspection department, from my experience.

I should've prefaced my initial comment with, "Assuming a flatness callout on the primary datum, and a competent inspector, one may opt for a profile of surface on the parallel surface..."

V

 

[CheckerRon]

Most of us reading this thread are thinking in terms of defining the part by Geometric Dimensioning and Tolerancing, but I get the feeling that our OP may not be.

The edge controlled can't vary more than 0.3, and it's the inspectors job to verify that, assuming your inspection is competent.

If your worried about abrupt changes within the 0.3 boundary or (say) a convex bow in the middle, then you need to control the form (straightness) tighter than 0.3 or modified per unit length

 

[wallyd999]

The last word belongs to checker ron. Good explanation.