Revision of drawing document of sub-assemblies and assemblies 1

[jassco]

Hi, Guys:

I have a question about revision of assembly (or sub-assembly) drawing documents. Since this is a drafting standard forum, I assume my question below is an appropriate one.

When you make a minor revision to a component, do you revise drawings of all sub-assemblies and assemblies where this component is used? I am familiar with ASME Y14.35M - 1997. But that is a legacy standard before 3D modelling. I do know there is a new standard ASME Y14.35-2014 released in August 29, 2014. I do not have a copy and I am wondering if the new standard says anything about assembly revisions.

Say, for example, you have a simple part. You add a hole to it or add some marking which does not affect form, fit, and function. So, you revise this component through revision. But what about all assembly and sub-assembly drawings? Do you revise them too as views of models on those assembly drawings are changed? We also use derived parts. So, this nesting can go very deep.

What's your thought on revision of assembly drawings?

Best regards,

Alex

 

[jassco]

Maybe, I try to do a survey below:

A component "A" is used in sub-assembly "B" which is used in sub-assembly "C" which is used in assembly "D", and etc. When you make a minor change to component "A", do you:

1. Ignore changes of assembly drawing documents;
Note: This is our current practice at my place.
2. Revise assembly drawings with revisions;
3. Revise assembly drawings without assigning new revisions.

Best regards,

Alex

 

[LynnB1]

For our company, all our prints and models are controlled in Teamcenter. Regardless of any drafting standard, we need to revise the assembly (with a new revision letter) in order to update the BOM and pull in the latest revision of the modified component. Otherwise the production released BOM would show a revision of the subcomponent that is superseded and out of date. So even if the change is just updating a tolerance or a note on the component print, assembly must be revised as well.

 

[looslib]

TeamCenter and Windchill will both require you to revise at a minimum the next higher assembly. Revising further up the BOM structure is optional, unless the change is visible in any upper level drawings.

Component A is revised and its drawing is revised to document the change.
Sub-Assembly B is revised to get the latest revised version of component A saved into its structure. Sub-Assembly B drawing is revised because the model was and the model and drawing are always at the same revision level.
Sub-Assembly C might be revised if the change to A is visible. The drawing would be revised to reflect the visible change.
Further up the BOM structure will depend on company policies and visibility of the change. Also the use of a PLM system will negate any higher level changes for the sake of a lower level change from this point on. Loading the highest level assembly with your options set to load-latest will bring in that component A change.


"Wildfires are dangerous, hard to control, and economically catastrophic."

Ben Loosli

 

[drawoh]

jassco,

Standard design change rules are that for any item with a given part number, you do not change form, fit or function. If such a change is required, you create a new part number.

In the context of your question, any modification to a part that does not affect the part number, does not affect the assemblies the part or sub-assembly is used on. You should not need to modify the assembly. If the changes are functional, you have new part numbers, and you are updating the BOM at the very least.

If the modifications do not affect form fit or function of the assembly, then there is effect on whatever that assembly is used on and no need for a new part number.

You need your manufacturing to trust you on this.

The alternative is to update revisions all the way down the assembly tree. You do not want that.

--
JHG

 

[jassco]

Hi, LynnB:

I think we used to use TeamCenter. But we switched to Solidworks ePDM 6 or 7 years ago.

When we make minor changes to a component, we retain its part number as the changes do not affect form, fit, and function. So, this means BOM of its parent assembly remains the same. So, if that is a case, how do you state your revision? Also, showing components' revision on its parent's assembly is a No-No based on my understanding. To revise all associated assemblies of a component, it can be a massive task. That is a reason why we don't do anything.

Hi, looslib:

What you mentioned seems a good compromise. But my problem is the change is visible to all associated documents. For example, if you change marking on an automobile tire, it will visually affect all associated documents, the number of which can be a dozen or two.

Hi, drawoh:

My thinking is inline with yours. But my concern is that how can we change affected assembly documents without going to revision process. Doesn't that violate principal of ASME Y14.35?

Best regards,

Alex

 

[drawoh]

jassco,

Your part number 123-456 NUTATING THINGAMABOOBER contains part 234-567 NUTATOR BRACKET, defined by drawing 234-567 revision[ ]C. Someone reports that the word DISCOMBOOBERATE is mis-spelled on sheet[ ]3 of the drawing. You write an ECO and update the drawing to revision[ ]D. Since the revision has no effect on the form, fit and function of the part, it has no effect on part 123-456. The BOM for 123-456 does not track the revision numbers of the fabrication drawings, thus, there is no need to update the assembly.

If manufacturing does not trust you to do revisions properly, they will insist on revision numbers on the BOMs. You will have to update the BOMs downstream of each and every revision. This is why you methodically follow design change rules.

--
JHG

 

[Nescius]

drawoh has it right.

I believe jassco is wondering if it's a problem that assembly drawing depictions might not be 100% representative. I submit that you just have to live with it. By definition, such superficial inaccuracies in a depiction on a downstream assembly drawing cannot matter.

Either the change to the part warrants a new part number, or it doesn't. There is no compromise. I have seen where some of our suppliers have an insane sliding scale of minor/major changes...and it is an illogical nightmare.

Parts and assemblies are never revised. They do not have rev. levels.
Never put part drawing rev. levels in the BOM or anywhere on an assembly drawing.

 

[jassco]

Hi, drawoh:

Thanks for your comment! But you did not answer my question. Let me use your example to better rephrase my question below:

Your part number 123-456 (an assembly) NUTATING THINGAMABOOBER contains part 234-567 NUTATOR BRACKET, defined by drawing 234-567 revision C. Say, you add a hole (a lifting hole) or change a chamfer to a fillet to your part 234-567. So, you write an ECO and update both 3D model and print of 234-567 NUTATOR BRACKET. No, what happens to 123-456 (an assembly) NUTATING THINGAMABOOBER? What about other parent and grandparent assemblies where 123-456 (an assembly) NUTATING THINGAMABOOBER is used?

Best regards,

Alex

 

[3DDave]

Just to kick in - if the function of the part in the assembly doesn't change, it doesn't matter what the revision is on the assembly it is used on. If you like, keep an as-built list to know exactly what revision is used. If the function of the part does change, then it gets a new part number and the assemblies that depend on that change get revised through the level the change matters. On rare occasions it is possible to withdraw all of a previous version of a part and replace the design with an incompatible one and not change the part number, but that requires careful tracking to remove all the old parts from the field, from stock, and from outstanding orders and is only recommended when changing the assembly part number to reflect the difference in function would be very costly - as in, the customer has already set up their supply chain management and won't change anything to cope with a supplier failure.

 

[jassco]

Hi, 3DDave:

Thanks for kicking in! Always like your inputs. But doesn't this statement "if the function of the part in the assembly doesn't change, it doesn't matter what the revision is on the assembly it is used on." violate principle of ASME Y14.35?

Best regards,

Alex

 

[3DDave]

What principle is that?

 

[jassco]

ASME Y14.35 requires that one documents changes with or without revision. Is it allowed to change a mis-spelled word on an assembly document without a revision process? My answer is no. Likewise, is it allowed to change views on assembly drawing without revision process? I don't know. But I do have a dilemma. Maybe I am thinking too much.

Best regards,

Alex

 

[drawoh]

jassco,

A nutator bracket with an extra hole in it is not form, fit and functionally identical to one without. You must assign a new number to it. It becomes 234-678 NUTATING BRACKET. If the modification does not affect the form, fit and function of 123-456, you revise the drawing and update the BOM.

If the NUTATING THINGAMABOOBER with the bracket with a hole in it is not form, fit and functionally identical to the one without, you need a new part number for the new assembly, perhaps 123-567! If the next assembly down the tree is functionally affected, it needs a new part number. Functional changes cascade down your assembly tree.

When the modified part or assembly is form, fit and functionally identical to its predecessor, there is no need to document a revision downstream. You want to contain minor, non-functional revisions.

If I am building your 112-543 HANDY DANDY COFFEE MACHINE and the BOM calls up 123-456 NUTATING THINGAMABOOBER, I need to go to the warehouse and get the part that works. There cannot be a part 123-456 that works, and a part 123-456 that does not work.

--
JHG

 

[3DDave]

jassco,

When someone has a functional need to alter the assembly drawing then a notation might be made, but there is no reason to make non-functional revisions.

 

[Nescius]

Likewise, is it allowed to change views on assembly drawing without revision process? I don't know. But I do have a dilemma. Maybe I am thinking too much.

If the part is interchangeable, don't update the assembly drawing views. Don't do anything to the assembly drawings. That's the goal. If the part number didn't change, there cannot be any consequences of leaving all the assembly drawings as showing (visually) the part made to the previous drawing revision.

 

[jassco]

Ok. Interesting! I just picked adding a hole as an example. If you change or add markings to a part, is that a "form, fit and function" change? If you change a chamfer of a part to a fillet, is that a "form, fit and function" change?

Best regards,
Alex

 

[jassco]

Hi, Nescius:

I agree with your comment. I always use backward compatibility as a criteria to assign new part number or not.

Best regards,

Alex

 

[drawoh]

(Mechanical)

... If you change a chamfer of a part to a fillet, is that a "form, fit and function" change?

This is a judgement call. If your chamfer closely matches a diagonal mating feature, it is a functional change. If the chamfer and fillet are non-sharp edges, you are reducing the cost, and the parts are form, fit and functionally identical. Does the modified drawing result in a part that works in all possible applications of it?

--
JHG