Completeness of a drawing

[Wunderbear]

Hello,

How complete does a drawing have to be and what is the general practice in the age of CAD? In many cases, I end up sending CAD files to the manufacturer and maybe just mark critical tolerances on the drawing with a general tolerance for unspecified dimensions. However, when this part comes in for inspection, the inspector might want to inspect even the dimensions left unspecified on the drawing - at least for the first time to qualify a new vendor for example.

Should I always strive to make the drawing complete to appease both sides and just highlight/mark critical dimensions? This might become unfeasible for complex parts. If I dont, the process of putting dimensions on the drawing becomes highly subjective - like one might want to put dimensions not not obviously critical on there to inspect to in the off chance that the vendor doesnt hit his general tolerance number.

 

[MintJulep]

It has to be complete enough to let everyone do their jobs.

Inspection is a job.

One of the things that a drawing must do is define how to perform an inspection.

 

[KENAT]

This question has been discussed multiple times - look at terms like Model Based Dimensioning and MBD to see previous threads.

I also urge you to reconsider what you mean by 'critical dimensions' - again this has been discussed before with varying view points given.

Suggest you use the search button in the silver ribbon bar, not the google search.

thread1103-420134 was a recent example.

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[drawoh]

Wunderbear,

Here is another interesting discussion: thread1103-322065.

I don't want to mark critical dimensions on my drawings. There are two conditions that require close attention from inspectors...
[ol]
[li]The feature is critical for the functioning of the component.[/li]
[li]The feature is difficult to fabricate accurately enough. We expect production to fail frequently, and we need a lot of inspection, and we expect to scrap or re-work components.[/li]
[/ol]

The fun starts when both conditions are true.

--
JHG

 

[MikeHalloran]

IMHO, the most critical function of a drawing is to specify exactly what you will NOT accept.


Mike Halloran
Pembroke Pines, FL, USA

 

[dgallup]

If you leave dimensions off or do MBD then you need to either be prepared to accept absolutely anything in the undefined areas or do some form of model based inspection. We have no way to do model based inspection so I put every dimension on the drawings. We are a TS 16949 certified company so we use the concept of critical characteristics defined by the standard. EVERYTHING that has a critical characteristic symbol HAS to be measured on a control plan but it is also assumed that EVERYTHING will be measured during a PPAP.

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