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Automotive industry standard for numbering mirror image parts? 1

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STLinjunear

Mechanical
Jun 10, 2011
1
I did search the Forums and FAQs but did not find a definitive answer for my question.

I work for a small engineering consulting firm that does highly specialized part design work for manufacturers and other engineering design firms, primarily in the automotive and related industries.

My most recent prior CAD experience was with an Aerospace parts manufacturer, where the common practice when producing identical, but mirror image (true left-hand, right-hand versions), part designs was to assign one base part number followed by -1 or -2 (for LH, RH versions), and produce one drawing of usually the LH part (-1) and specifiying the RH part as -2. Part numbers on orders would then reflect the complete number including the dash number. This is fairly common in the tooling industry as well.

This works well in SolidWorks (and other CAD systems I am sure) when using configurations to produce separate, but linked, CAD model files for CNC, STL, RP, etc. production. We are working with another engineering firm (the client) on design of some of his parts which fit into others he is designing to produce an engine. In a recent design review meeting, the client balked at our use of the dash numbers, even though the numbers are for our internal use only, and he reassigns new numbers to the completed designs.

I personally prefer the use of the dash numbers for easier file maintenance by using only a single part file containing mirror image configurations (named with complete part-dash number) and a single associated 2D drawing file. In deference to the client, I am maintaining fully dimensioned drawings of both versions, but as separate drawing sheets within the same drawing file.

While the client was pushing this, suggesting we maintain separate but linked files, and doing away with the dash numbers, my boss, not wanting to offend/disagree with the client, agreed we would look into what was the automotive industy standard practice.

So which is it? Dash numbers (RH-LH configurations) or not for mirror image parts in the automotive industry? Also, is it "legal" ("kosher", QA-blessed ,etc.) to have a "drawing number" (the base filename number) which is different (without dashes) than the actual "part number", which would be the drawing number with the addition of the respective dash number. I know this works in aerospace, but is it used in automotive? Are there any standards that call this out?

Similarly, what is the soundness of using tabulated drawings (again, single CAD file) with dash number designating part variations (with or w/o holes, holes sizes, locations, dimensional differences, etc.). I know that we did that a lot in the tooling industry, especially with part size variations. However, does automotive industry frown on this practice, or is it perfectly acceptable? As above, are there any standards that call this out?
 
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I am most familiar with GM drawings, and they use separate part numbers for mirror image parts.
 

The Rule of thumb in automotive industry is “never assume LH and RH parts are mirror images”.

Think of LH and HR fenders having features for mounting aerial antenna or fuel tank door.

So not only they are usually given separate part numbers, it is not uncommon for them to undergo different number of revisions, etc., so essentially LH and RH parts are “living completely separate lives”.

The exact rules will change from company to company.

The drawing standards for suppliers usually published on company’s website (At least I remember Ford doing that). You have to be registered and have a login.

I hope this helped.
 
The Rule of thumb in automotive industry is "never assume LH and RH parts are mirror images".

The same is true in aerospace. If the part numbers indicate that it is so (-1, -2), it is not an assumption but a statement of fact. If parts are opposite but not mirror, then the part no.s would not be structured the same (-1, -3 instead of -1, -2; or a new p/n).

"Good to know you got shoes to wear when you find the floor." - [small]Robert Hunter[/small]
 
STLinjunear it all depends on your customers configuration control.

We looked into this a few years back, most of the folks in my dept were from US defense/aerospace/automotive backgrounds and had used - numbers.

However, our employer did not readily allow for - numbers in their configuration control system, also trying to do it with the CAD system - especially as we were looking to tie it in with PDM - was challenging.

As far as we could tell, - numbers are perfectly valid per ASME stds, but so is not using them.

Posting guidelines faq731-376 (probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484
 

Car companies are big enough to write their own standards, especially when it comes to configuration management.

Some use dash numbers for revision control. So -021 could be 21st version of the part.

You have to be REALLY open-minded to switch between industries.
 
True that.

"Good to know you got shoes to wear when you find the floor." - [small]Robert Hunter[/small]
 
There are two good books that defend two different approaches to drawing numbers and part numbers:

1- "Engineering Documentation Control Handbook", by Frank Watts
2 - Bills of Material for a Lean Enterprise" by Dave Garwood

They are 'deep' and current. They would help identify the logic (or lack of it) in various methods and help design a system for you that would best accommodate customer's numbers under yours.

Peter Truitt
Minnesota
 
More to the point of the question, I strongly agree with checkerhater's comment: "Never assume LH and RH parts are mirror images". Be careful trying to link configuration control to CAD configurations. Designs and/or parts change. CAD systems change. What might be a perfectly mirrored part today, might not be tomorrow, unless you have a perfect design configuration system under bulletproof audit control.

Peter Truitt
Minnesota
 
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