Fit, Form and Function

[jwhit]

Every now and then I run across someone using the term Fit,Form and Function, which to me is established in the engineering stage and verified in the inspection stage. The issue I have is when they attempt to extend that terminology to inspection for material discontinuities. To my way of thinking, you have an acceptance criteria established either by the specification or by the customer, therefore, the only people who can make a qualified decision on whether a discontinuity will affect fit, form and function is the customers engineering staff. Before I get into a heated debate over this, I would like some thoughts from those outside of the situation. Thanks for any input you choose to make.

 

[CoryPad]

Everything you wrote seems logical to me.

 

[metengr]

What you have stated is common practice. I as the customer make the final acceptance based on either a standard or internal engineering specification.

 

[jwhit]

I appreciate the responses. The logic that we run into sometimes is incredible,at least in my opinion. Every day, I'm glad that my time dealing with this stuff is dwindling. Retirement or semi-retirement can't come soon enough.

 

[KENAT]

Not sure I entirely agree with you, fit & form should be pretty well defined by the engineering drawing and if a discontinuity impacts this (i.e. cause part not to meet drawing tolerances) then that should be identifiable by inspection.

Function, as impacted by material discontinuities may not always be clearly defined on typical drawing.

Ideally if material discontinuities are likely to impact function then there should be some kind of spec on the drawing but it's probably something that often gets overlooked.

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[dgallup]

Just what sort of "material discontinuities" are we talking about? Are these visible pits or gouges on a surface? If so, then the relevant dimensions including geometric tolerances and surface roughness call outs on the drawing should cover it. If, on the other hand, you are talking about "material discontinuities" such as seams in a piece of bar stock and it is critical to the structural integrity (function) of the end product then you need to add something like eddy current or ultrasonic inspection to the bar stock purchasing requirements. We do this all the time in our material specifications.

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

 

[1gibson]

I'd generally accept deviations that "did not affect fit or function" when working at a pump OEM. Form, to me at least, includes aesthetics. A perfectly functional part might look like crap from the outside.

If (when) a customer came in and said "that's ugly, fix it or get me a new one" then it usually wasn't worth arguing. Just explain that I can weld it and remachine, but it might pull the critical dimensions and affect concentricity, so we might have to repair it again to fix the fit/function that is perfectly fine at the moment.

 

[geesamand]

I agree completely. Even a quality engineer with engineering training will not be able to assess the integrity of a component with a flaw. It has to go back to the engineers and operations personnel who know what will and will not work for them.

Lacking that communication pipeline, I would interpret "Form fit and function" to be an arrogant joke meaning "just reject it".