Drafting Standard??

[drewcon18]

I have a basic mechanical rod consisting of several parts that is manufactured at a machine shop. My techincal drawing is about 15 years old, but covers everything I need (GD&T is fine). The quality assurance director at my office wants me to highlight or bold certain dimensions and tolerances so that the machine shop knows that these are "key" dimensions. Is it common practice to specify a technical drawing in this manner? I argued that every dimension is critical and should be verified within tolerances. If I highlight certain dimensions, wouldnt the machine shop focus on those and not others to save time? Im a young engineer, so any help would be appreciated.

 

[KENAT]

Oh dear what have you started. thread1103-165581

This comes up every now and again, to the best of my knowledge and general consensus of those on this site no it's not normal practice. If the dimension isn't required to manufacture the part it shouldn't be on the drawing (except maybe as reference). If the dimension isn't 'critical' it should have a relatively loose tolerance which is easy to meet and measure.

If they want to reduce inspection from 100% of all inspections they should use a technique such as statistical.

Now if they want guidance in what are more critical areas for them to tune their statistical inspection I'd have a little more sympathy but still shouldn't be on the drawing.

 

[dingy2]

The Quality Assurance Director is incorrect here. What he really wants to know is the function and relationship of the part and how it is used during the assembly.

QA will require a Control Plan for this part and one does not want to spend time and $$ checking on a regular basis features (characteristics) that are not important to its function.

Do not highlight this information on the drawing but give the QA department a "feel" of the product.

I remember when I was a Quality Manager and we had a new stamping from a GM division. I phoned the Designer and asked THE question (what's important). Of course, I received "everything is important". I really wanted to know the function and relationship of the features. I eventually received the information from the GM Quality department and it was helpful.

Ask the QA Director if the information required is the function & relationship of the part.



Dave D.

http://www.qmsi.ca

 

[ctopher]

The thread Kenat ref is good.

Chris
SolidWorks 06 5.1/PDMWorks 06
AutoCAD 06
ctopher's home (updated 10-27-06)

 

[KENAT]

If they want to reduce inspection from 100% of all inspections they should use a technique such as statistical.

Sorry, should be:

If they want to reduce inspection from 100% of all dimension on all items they should use a technique such as statistical.

 

[JohnNabors]

When I worked in the automotive industry they used a symbol to designate critical features as 'Key Product Characteristics' (example: DaimlerChrysler used a diamond symbol adjacent to the dimension on the drawing). Any feature designated as a KPC was required to be statistically controlled with a minimum Cpk of 1.33.

That said, I always felt it was a bad practice to designate criticals.