Bill of materials pt # verses Assembly drawing pt # 1

[amckenna]

Bill of materials part number verses Assembly drawing part number: should they have the same part number, or different?

At my company, we’ve had some disagreement on the above topic. I would like to get some outside options on how to handle this. Currently, we have a program that helps us structure our bills of materials. We’ve been assigning the same part number to our BOM’s and assembly drawings. Both BOM and assembly drawing have revision control. Using this configuration, should the BOM and assembly drawing always have the same revision letter? Should the BOM have a different number entirely, so that if a purchased component is changed it won’t affect the assembly drawing revision? Any options would be greatly appreciated.

 

[ewh]

The dwg and BOM don't have to have the same rev level. They can share the same basic drawing number, but need to be differentiated somehow, such as "1234-56" for the dwg and "PL1234-56" for the BOM.

 

[amckenna]

Thanks for the reply. You methodolgy is exactly what I was thinking of implimenting.

 

[KENAT]

Agree with ewh.

At my last place we didn't use the BOM to define the build standard of the item.

We had what was called a drawing list for top level assemblies. This was a list of all the drawings with their rev. It was maintained as part of the drawing pack. It had the same number as the drawing it related to but with DL prefix when required. Parts without a drawing were only listed on the relevant part list.

The drawing list did not have to have the same rev as the top level drawing it related to. It had its own rev and it was this rev that controlled what the latest build standard of the item was.

Manufacturing created the BOM based on the Drawing list and all assembly & subassembly drawing parts lists there on.

At my current place the BOM is the controlling document as regards the rev level of all drawings and is kept at the same rev as the drawing, when there is one. Historically here many higher level assemblies are only a BOM - no drawings, it causes problems and we are trying to correct it.

 

[mrMikee]

Drawing numbers and part numbers should be different but in general are similar enough that it is easy to find the drawing/file if you know the part number. Another reason that part numbers and drawing numbers shouldn't be the same is because many times a drawing will show more than one assembly, left hand and right hand, for example. Or maybe it will show two or more very similar assemblies.

In my opinion the drawing and part should have the same rev levels in order to keep track of corresponding parts lists and associated drawings. When a drawing changes sometimes there is no change required to the parts list, but I would still rev the both. It depends on what you require and if everyone understands the rules.

I suggest going back over threads in this forum, I've seen some fairly good discussions on this topic.

Regards,
-Mike

 

[ewh]

Per ASME Y14.35, para 7.1.1(b) - "Revision letters are assigned in an independant sequence against each different type of associated document."

To revise a drawing when a simple change was made to the PL is unnecessary work. To revise a PL when a simple change is made to the drawing is the same. The $$ will quickly add up if you make it a rule to keep the revision levels the same (the time required to write the change order, to make the change, to check the change, to release the change). Change orders can be quite an expense, and I wouldn't want to increase the cost when it is not needed.

 

[amckenna]

Thanks for all your inputs. The only "grey" areas with my companies part numbering system is this shared part number between assembly BOM and assembly drawing. As Ewh stated, adding a "PL" to the BOM part # will hopefully straighten things out.

 

[mrMikee]

amckenna,

I see now that I didn't answer the question you were asking. If you are interested in more information on this subject I suggest the following book..

"Engineering Documentation Control Handbook, Configuration Management in Industry." Frank B. Watts
This is a good book with both practical information and the theories or reasons backing up his recommendations. It covers part numbering, revision control, and configuration management.

-Mike