part drawing revision and assembly drawing revision

[bxbzq]

Hi there,

When you revise a part or sub-assembly drawing, do you revise also all upper level assembly drawings?
Do you include part/sub-assembly drawing revisions in parts list in an assembly drawing?

 

[jassco]

Hi, bxbzq:

A drawing for a part (or component) or a sub-assembly has nothing to do with their parent assembly drawings. When you make a revision to a component or sub-assembly drawing, no revision is needed to its parent drawing(s) unless the parent drawings get changed due to the changes of components. You only need to change parent assembly drawings when they get changes. You can't revise an assembly drawing if it has no change(s).

Best regards,

Alex

 

[KENAT]

If you truly revise a part or sub assembly drawing then you are stating it is fully backward and forward interchangeable and so as such the next level assy drawing does not need to change (drawing list if your system has one would change).

If the part of sub assembly is not fully interchangeable then it should be a new part number. In this case the change will ripple up through the drawing structure until the level interchangeability is restored.

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[bxbzq]

Can you shoot me some examples of change that don't affect the interchangeability? I can't list many, to be honest.
Also about interchangeability, is it only about functionality or can be something else?
If a component has M6 - 6.6 grade screws(I'm living in metric world). Now for some reason (purchasing for example) it will use M6 - 8.8 grade screws. It has functionality upgrade even it is not needed. In this case do you revise the component drawing or do you create a new part number?

 

[jassco]

Hi, bxbzq:

First of all, if your print calls for M6 - 6.6 grade screw, then it is technically wrong for your purchasing to purchase M6 - 8.8 grade screws.

You could revise it to M6 - 8.8 if this change is acceptable for all assemblies where this screw is used. But according to form, fit, and function, it is better to assign a new part no.

Alternatively, you can revise the print to allow use of either M6 - 6.6 or M6 - 8.8.

It is a good idea to say what you do, and do what you say. But it is not easy.

Best regards,

Alex

 

[looslib]

Changing the grade of material on a purchased part would be a new part number. However, the only reason to change the assembly drawing would be if you had a BOM on the face of the drawing and you needed to inorporate the new number.

We had a policy that the change was to be done to the next higher assembly up to the point where the change was not 'visible'. This could be changes to the BOM or geometry. If the changed component was put into a sub-assembly and then the sub-assembly was placed inside an enclosed structure, then you would only have to change the 3 levels, since in higher levels the changed component is not visible. Our assemblies had between 3 and 8 levels of sub-assemblies.

Never put drawing revision levels in a BOM for an assembly. If you do, you will always have to change every drawing up to the top level with each change. Keeping track of that would be nightmare if you have a lot of engineers working on different aspects of the same machine.


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

Ben Loosli

 

[dgallup]

There are many changes to a part drawing that do not require updating assembly drawings. There could be simple 2D drawing changes such as notes, symbols, etc. There could be changes to the model such as tolerances or the addition of a radius or chamfer that doesn't affect interchangeability. In the latter case the assembly drawing may be pictorially incorrect but it doesn't matter. Those changes can catch up when the assembly drawing needs some other change. In the bad old days of board drawings (or AutoMAD), sometimes those assembly views NEVER got updated because it would involve acres of erasing and redrawing.

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[drawoh]

bxbzq,

A general rule of thumb in design and drafting is that you do not change form fit and function. This is why. If you violate this rule, each drawing change, even if trivial, percolates down through your document tree.

--
JHG

 

[drawoh]

Can you shoot me some examples of change that don't affect the interchangeability? I can't list many, to be honest.

You corrected the spelling of "DISCOMBOOBERATE" on sheet[ ]4 of your drawing. You added missing dimensions. You clarified a note that was confusing people.

--
JHG

 

[KENAT]

Sadly the old form fit & function line that gets trotted out may not cover all eventualities.

Interchangeability may be physical form/fit/functional interchangeability but may also capture other factors.

For instance, say you change a part to be ROHS compliant. You may need to be able to track this fact. This would require new PN even though the part may be fully interchangeable with the non ROHS version.

Likewise say you add some extra testing or similar to a part to improve quality. This may be physically form fit function interchangeable with the old part but if you need to be able to track that you are using the new tested version a part number change is probably required.

ASME Y14.100 has the basic rules for when Part Number change is required, if you work to that family of standards I suggest you take a look.

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[bxbzq]

Thanks for all replies. They help.

 

[drawoh]

KENAT,

If your part must be ROHS compliant, then any part not ROHS compliant is not that part and must have a different part number. I see no difference between ROHS compliance and perhaps the colour blue versus smoke mauve.

--
JHG

 

[KENAT]

Some would argue that the ROHS version is physically form, fit, function interchangeable.

However, needs to be given different PN for traceability for regulatory compliance.

ASME Y14.100 alludes to this type of thing in it's explanation of when a new PN is needed.

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