advice needed on revision control

[hobbs101]

Hi All

I'm a freelance engineer working on small design projects (typically <100 designed parts). Projects are generally industrial machines that sell in small numbers. With each sale of a machine, design improvements are made.

I'm looking to devise a simple revision control system. I use Autodesk Inventor. No PLM/MRP system.

I understand from other posts on this forum the rules on form/function/fit. For me that will generally mean that whenever I modify a part, it's part number will change. I'm happy with that.

I'm keen to have the part number the same as the (root) drawing number, i.e. if the part is P-100-12301, then the first released revision of the drawing will be P-100-12301-A. (I'm happy to reconsider this if it makes life a lot easier!).

I won't state drawing revision levels on sub-assy and GA drawings, as I understand this is not necessary as revision levels should be interchangeable.

So, when I modify a part that changes form/function/fit I change the part/drawing number. Does this then mean I need to update the BOM's on the sub-assy drawing and the GA? I guess if the part change changes the FFF of the sub-assy then that also needs to change assembly/drawing number, and so on.

Thanks.



Hobbs101
Mechanical Design Engineer

 

[hobbs101]

I've just seen post thread781-380214 which asks a similar question.

Seems like a lot of work. If I have one small change at the part level that affects interoperability at the top level, then all sub-assy drawings have to be modified up the chain. But, I guess there's no way round this from the control point of view! In practice, I guess a number of changes might be included in an update, thereby reducing the number of times the top level number is changed.

Btw, why do you go from -1 to -3, missing out -2?

My intended scheme is

- part number P-100-123-01 (P = part, 100 = project code, 123 = part no. prefix, 01 = part no. suffix)
- drawing number P-100-123-01-A (note, drawings that are at draft for checking/approval will be P-100-123-01-A-01, -02 ...)
- if FFF is changed, then part number will change to P-100-123-02, and drawing to P-100-123-02-A

Is this workable?

A small point, but is the -A referred to as a 'revision' or an 'issue', or indeed a 'version'?!! Is an alphabetic character ok rather than a numeric one?

Hobbs101
Mechanical Design Engineer

 

[sammcc]

why do you feel you have to change your part numbers each time you make a change to them?
Is it not more simple just to up them in issue.
That way your bom structure never changes.
Each time a part chamges up issue the drawing and write a suitable ECN with a unique number and put this beside the drawing issue field on the drawing, that way you will be easily able to tell what the change was.

 

[hobbs101]

Well, that's how I used to do it. But, I now want to do it according to the form/function/fit rules. In my work, most part changes will change the FFF, and therefore require a change in part number because the parts won't be interchangeable. Isn't that the 'correct' way of doing it??

Hobbs101
Mechanical Design Engineer

 

[swertel]

When changing part numbers, there are actually two things to consider.
The first, as you mentioned, is form/fit/function.
The second, which is often overlooked, is two-way traceability.

If there is a problem in the field, can my customer give me the part or model number (the item they actually purchased) and can I tell exactly which part at which revision went into the item?
If there is a problem with a part, can I tell which items that part was included in?

Feel free to use the attached, so long as proper credit is given.

--Scott
www.wertel.pro

 

[hobbs101]

Swertel, I think what you're saying is that it's even more important to change the part number if traceability is required.

For my work, traceability is absolutely required. I need to know exactly what parts make up an assembly.

What do you think to my intended numbering scheme?

Hobbs101
Mechanical Design Engineer

 

[KENAT]

The real important thing is interchangeability - to me this covers the traceability issue swertel brings up but the traceability does often get overlooked. If you can put parts of any revision in a big 'bucket' and pick any of them and it will work ok in your assembly then it's a revision.

While in your situation smart numbering scheme may have some advantages, general consensus seems to be dumb numbering schemes end up being better long term. e.g. start with 000-000-001 and work your way up or similar.

Swertel & I are basing this on what the ASME stds e.g. Y14.100 say about it. Some places do use significant revisions but that's not the preferred way of doing it per my understanding of ASME.

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[hobbs101]

Yes, interchangeability is key.

I see no reason not to use 'smart numbering', although I also understand that it's not essential.

Is someone able to comment/answer the queries from my previous post -

Btw, why do you go from -1 to -3, missing out -2?

My intended scheme is

- part number P-100-123-01 (P = part, 100 = project code, 123 = part no. prefix, 01 = part no. suffix)
- drawing number P-100-123-01-A (note, drawings that are at draft for checking/approval will be P-100-123-01-A-01, -02 ...)
- if FFF is changed, then part number will change to P-100-123-02, and drawing to P-100-123-02-A

Is this workable?

A small point, but is the -A referred to as a 'revision' or an 'issue', or indeed a 'version'?!! Is an alphabetic character ok rather than a numeric one?

Hobbs101
Mechanical Design Engineer

 

[KENAT]

I think Swertel was using -01 & -03 just as examples to illustrate 'dash numbers' where you have multiple 'part numbers' covered by single drawing.

So in his case -02 may have been 'Saxe Blue' - he just didn't use it as part of his example.

What you're suggesting may not be a typical application of 'dash' numbers.

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[swertel]

Odd-number and even-number dash numbers (configurations) are a legacy military standard.

The original part is a -1. The mirror of a -1 is a -2.
If I need to make a completely new, non-interchangeable configuration (aka dash number), it's a -3.

I can't quote from memory the exact specification, but it reads along the lines of
"even number dash configurations are the opposite hand of the preceding odd number dash configurations."


--Scott
www.wertel.pro

 

[swertel]

Documents have revisions; physical items do not.
If you apply a revision status to a physical item, you essentially created a "new" unique identifier for that physical item. Adding an alpha code at the end of a base number is no different than adding a numeric dash number.

@hobbs101
Changing the part number is the easiest way to guarantee traceability, but not the only way. As my flowchart shows, if you assign serial numbers or lot numbers to your physical items, then your as-built records provide the necessary traceability. That is, if you have as-built records and properly manage effectivity of change. (A can of worms not worth exploring in this thread.)

Numeric or Alpha Revision Characters
It doesn't matter. But, historically, numeric revision identifiers are used to designate pre-production documentation. In other words, when the design is in a prototype or development phase. Alpha characters are used to designate production level drawings. I have even seen a third designation, revisions preceeded by "X" example: X1, X2, X3, or XA, XB, XC.
[ul]
[li]Level I - Conceptual (napkin sketches, brainstorming ideas, etc) | Rev 1, 2, 3[/li]
[li]Level II - Development (formal drawings but not all material data or dimensions included, used for first run, test, prototype manufacturing) | Rev XA, XB, XC[/li]
[li]Level III - Production (complete technical data package, all i's dotted, all t's crossed) | Rev A, B, C.[/li]
Some people like to start out initial revisions at "Rev -" or "Rev N/C" (no change). I hate it, computer systems don't like it either.[/li]
[/ul]

Significant (aka Smart) or Insignificant Part Numbers
It's totally up to you. But you definitely need to have an insignificant portion to any part numbering system or it will soon fail.
My favorite part numbering scheme is to have an intelligent prefix followed by an insignificant sequential number followed by a dash configuration, although the prefix can also be insignificant and sequential.

Example:
Part Number AAA-100000-1 where:
AAA = prefix designating a certain model of a machine, product, tool, or other end-item deliverable.
100000 = the insignificant sequential number.
-1 = the unique configuration identification.

Part number AAA-100000-1 would be defined on drawing AAA-100000^A (I use the caret symbol to delineate the revision).
If I need to make an interchangeable change to AAA-100000-1, I would revise drawing to AAA-100000^B.
If I need to make a noninterchangeable change to AAA-100000-1, I would revise drawing to AAA-100000^C and create AAA-100000-3, still defined on the same drawing. I may have to add another sheet to fully define it. I may have to deal with some pretty labor intensive drafting standards to avoid confusion, but it works. If I AAA-100000 is an assembly drawing with an integral parts list, I may have to play around with how I want to show and balloon the components of AAA-1000000-1 and AAA-100000-3.

By the way, my next prefix for a new machine would be AAB. Thus, insignificant and sequential. But you could make the prefix "smart" by abbreviating the product name, as one example. Just make sure you have a log of prefixes so you don't re-use one.

--Scott
www.wertel.pro

 

[hobbs101]

Hi Wertel

Now I'm confused! I don't understand your favorite part numbering system. I can see that the part number would change from AAA-100000-1 to AAA-100000-3, but I don't understand why the drawing number doesn't go from AAA-100000-1^B to AAA-100000-3^A. The -3 is a new part, so why not create a new drawing?

On your drawing AAA-100000^C, how is part AAA-100000-3 referenced?

Hobbs101
Mechanical Design Engineer

 

[swertel]

All the dash numbers are shown on the same base drawing.

It's completely optional to have a 1:1 relationship between parts and drawings, or a many:1 relationship to show multiple configurations on the same drawing. Whatever works better for you.

Our standard is to show multiple configurations, those with the same base number, on the same drawing. This is very similar to the tabulated drawing technique.

--Scott
www.wertel.pro

 

[hobbs101]

Thanks swertel. It's all becoming clearer. Thanks for your help.

Hobbs101
Mechanical Design Engineer

 

[KENAT]

A word against having 'project' or 'machine' designator as part of the intelligent part number.

What happens when you want to use the same part on another project/product?

People used to strict adherence to 'all the parts for this machine start with XXX' may be confused by apparantly random 'YYY' & 'RRR' parts showing up in it.

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[hobbs101]

Kenat, I agree with that. In fact that's likely to happen in my current project. Parts will definitely be used on the next one. Something to think about ...

Hobbs101
Mechanical Design Engineer

 

[MikeHalloran]

You could maintain a set of 'standard' parts prefixed 'SSS' or similar, at least for the parts you re-use in serious quantities.



Mike Halloran
Pembroke Pines, FL, USA

 

[KENAT]

Mike, that idea works ok when you know in advance it's going to become a 'standard' part but sometimes you don't know in advance.

I'm currently working on projects re-using a whole bunch of legacy parts in new ways - people get confused just by the descriptions let alone if they were tracking intelligent part numbers too.

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[swertel]

Kenat and Mike,

There is a prefix for Standard Parts (I always joke that I should make it "STD" because they are shared among many partners).
{Who says engineers don't have a sense of humor.}

1) Create a part that I think is unique to a project, customer, machine, etc. It's assigned the specific prefix.
2) Find out I want to use that part on another project.
3) Re-create the part, but with the standard parts prefix. It's a new part number.
4) Cancel the specific drawing and in the cancellation notice state that it is superseded by the standard part. This creates your breadcrumb trail so I don't have to revise the next level assembly to point to the new standard part. Revising the next level assembly is still a good idea, though.

[ul]
[li]Having a prefix for standard parts provides the human readable information to know that this part is used on multiple project, even when managed in a PDM/PLM system.[/li]
[li]This also helps with supply chain management. A standard part should have better economies of scale.[/li]
[li]This also helps with revision control and configuration management. If I'm using a standard part but want to tweak it, I know that it is used on multiple projects so I have to perform the impact analysis to make sure the change doesn't have a negative effect on other systems.[/li]
[li]This also helps with project-unique requirements. Because sometimes a customer gets a little too involved in the design and you don't want them to have control over your standard parts or other designs. While you lose economies of scale, you can have the same physical item defined by different part numbers. Warehousing, ordering, etc. will all be affected.[/li]
[/ul]

--Scott
www.wertel.pro

 

[KENAT]

I don't know, sounds like some doc control overhead to me, I'd have thought this should be able to be handled by some other data base be it ERP, the drawing log, PLM...

However, maybe I'm missing something.

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