CRITICAL on drawings
CRITICAL on drawings
(OP)
Hello all,
I have a question about the addition of "CRITICAL" to a specific dimension on a drawing. Our sales guy wants to add it as a sort of flag to say "Hey guys, if you're going to miss a dimension, don't let it be this one." The tolerance on the dim is sufficient and it's really not any more critical than any of the other dimensions the only difference is if it's out of tolerance, it will show up later in a big way. I'm against putting this note on the drawing as I feel it may cause someone to think that dimensions not indicated as critical, are somehow unimportant. Is there standard out there that addresses the use of CRITICAL on a drawing? I hope I've been clear on the issue.
Thanks
I have a question about the addition of "CRITICAL" to a specific dimension on a drawing. Our sales guy wants to add it as a sort of flag to say "Hey guys, if you're going to miss a dimension, don't let it be this one." The tolerance on the dim is sufficient and it's really not any more critical than any of the other dimensions the only difference is if it's out of tolerance, it will show up later in a big way. I'm against putting this note on the drawing as I feel it may cause someone to think that dimensions not indicated as critical, are somehow unimportant. Is there standard out there that addresses the use of CRITICAL on a drawing? I hope I've been clear on the issue.
Thanks
Powerhound
Production Supervisor
Inventor 11
Mastercam X
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II





RE: CRITICAL on drawings
Now I can't say my heart is really in what's there. To me in essence if the drawing is correctly toleranced then I would expect that any values outside of the tolerance of any dimension may cause problems while any value withing the range is OK. I would also expect all parts to meet said tolerances. In practice though maybe this is an over simplification.
Personally I think of it more as being an indication of a dimension that should be 100% inspected rather than just sampling/statistical but someone more familiar with the concept may be able to shed more light.
We use a diamond symbol which is explained by a note that references the company policy rather than writing critical next to the dim.
Hope this gives you a starter for 10!
Ken
RE: CRITICAL on drawings
If you have dimensions that can be "out of tolerance", but the part is still acceptable, the tolerances are incorrect.
RE: CRITICAL on drawings
if it helps
RE: CRITICAL on drawings
The tolerance is correct as the part will not work if the dimension in question is out of tolerance. The issue is whether or not it really makes sense to add the CRITICAL note to the dimension. To me, it makes no sense except to complicate the issue but I wanted to hear from people in the same discipline to get their opinions.
KENAT,
So you have a company policy governing the use of symbols and such on drawings? Can you elaborate a little? Maybe we need something similar.
Powerhound
Production Supervisor
Inventor 11
Mastercam X
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II
RE: CRITICAL on drawings
I agree, it just complicates things, and used as suggested by the marketing guy, is not consitant with the definition provided by Kenat.
RE: CRITICAL on drawings
Thanks for the input. Based on what I've read, I'm going to leave the drawing as it is. I'm sure I'll hear about it but I think I'll survive.
Thanks again,
Powerhound
Powerhound
Production Supervisor
Inventor 11
Mastercam X
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II
RE: CRITICAL on drawings
I told him that I had saved him the trouble, by removing the non- critical dimensions from my team's drawings entirely.
I suspect his true goal had more to do with adding paperwork and 'reports' to shuffle it, than it did with making the product better.
Mike Halloran
Pembroke Pines, FL, USA
RE: CRITICAL on drawings
Chris
Systems Analyst, I.S.
SolidWorks 06 4.1/PDMWorks 06
AutoCAD 06
ctopher's home (updated 06-21-06)
RE: CRITICAL on drawings
Jim Sykes, P.Eng, GDTP-S
Profile Services
CAD-Documentation-GD&T-Product Development
www.profileservices.ca
RE: CRITICAL on drawings
Looking up the latest set of ASME Y14.X standards, you will also find standardized flags for Critical Safety Items as well as other "critical" callouts.
--Scott
http://wertel.eng.pro
RE: CRITICAL on drawings
Boottmills![[soapbox] soapbox](https://www.tipmaster.com/images/soapbox.gif)
SW2006 SP3.0
RE: CRITICAL on drawings
Automotive OEM place a symbol for critical to reflect SPC applications and most of those are not really critical or are on inappropriate features such as positional tolerances. Some companies were overusing this and it just increased the costs with little benefit.
It is up to your Quality department and the Supplier's Quality department to control important characteristics. The "Control Plan" or in non-automotive companies, the "Inspection Plan" would show the controls - methods of measuring, frequencies, sample size, etc. for confirming the important features are within specifications. That is the way to go.
RE: CRITICAL on drawings
As well as the above the main parts of relevance are:
Like I said in my first post my heart isn't in it and actually I think the definition of minor characteristic could lead to problems.
If the 'reasonable variation' is within tolerance then why bring it up. If it is outside of tolerance but doesn't cause a problem then the drawing tolerance should be relaxed but maybe that's just me.
RE: CRITICAL on drawings
Chris
Systems Analyst, I.S.
SolidWorks 06 4.1/PDMWorks 06
AutoCAD 06
ctopher's home (updated 06-21-06)
RE: CRITICAL on drawings
RE: CRITICAL on drawings
--Scott
http://wertel.eng.pro
RE: CRITICAL on drawings
For example at my last place I designed a folding lug for a US program. This lug was the main suspension for the store. Accordingly the area around the pivot was critical, I think class B, so had to have a heavy inspection criteria. The rest of the lug had much higher safety factors and different failure modes so was only class D or something like that requiring much lower sampling.
Like I said this is all from memory and I may be confusing with another spec but I think this is it.
RE: CRITICAL on drawings
A critical characteristic is something that would cause personal harm or death (safety issue) at the system level.
A major characteristic is one that would cause of failure at the system level (resulting in a mission failure) but not so extreme as to injure anyone.
A minor characteristic is everything else, but a listed minor is a characteristic that has a significant quality impact or requires special inspection techniques.
So basically, what this thread has described as a "Critical" is really just a listed minor if following the spec.
--Scott
http://wertel.eng.pro
RE: CRITICAL on drawings
The way the sales guy is proposing to use the term 'critical' or the way our company spec defines it is more along the lines of at most a major characteristic. Furthermore I'd expect this failure to normally be apparant during assembly, ie parts don't fit or it doesn't pass system test, than in service.
However, from what I remember the spec is more about invoking NDT etc rather than about dimensional inspection although sometimes dimensional variation could directly lead to failure.
RE: CRITICAL on drawings
A "critical" dimension would make them aware that it had to be in spec period, or that it may affect end item buy off.
Also could affect the interchangeability of components forward and backward
I will say that it is used less and less over the years since I started with the John Glen flight in 63.
Now that we are in MBD (model base definition) we rely on interchangeable requirements and assy level tolerance with no defined detail level tolerance
Cheers
I don't know anything but the people that do.
RE: CRITICAL on drawings
The trick with DOD-STD-2101 is to not let the tolerance of a dimension drive the decision as to a critical, major, or listed minor characteristic. Also, 2101 is not meant to be the driver for additional inspection (AQL) criteria. It is merely a flag to say that "This characteristic is important" and therefore whatever inspection level I define (either following ANSI AQLs or MIL-STD-1916) needs to be clearly documented because the customer is going to ask for inspection records of those characteristics.
Many people fall into the trap of wanting to inspect a dimension 100% and therefore call it "Critical" even when it is only critical in terms of scrap rate or assembly fits. Likewise, many designers/engineers/management insist that a tightly toleranced dimension must be a major or it would have a looser tolerance; but the tolerancing is determined based on fit, function, and part interchangeability and not on system failure.
It is true, though, that many dimensions that are critical, majors, or listed minors won't fit together if they are out of tolerance. If that's the case, then your inspection criteria can be "did it fit together." Talk about an easy and verifiable 100% inspection method.
--Scott
http://wertel.eng.pro
RE: CRITICAL on drawings
See last paragraph at bottom.
Chris
Systems Analyst, I.S.
SolidWorks 06 4.1/PDMWorks 06
AutoCAD 06
ctopher's home (updated 06-21-06)
RE: CRITICAL on drawings
It was to do with safety/system failure and that then led us to more tightly define NDT inspection requirements than normal.
As regards the use of critical as my companies procedure defines it or powerhounds sales guy wants to use it I'm still inclined to think that this is probably better put in a QA plan rather than the drawing.
RE: CRITICAL on drawings
Based on that website, it appears that the standard uses a model-based design approach. In other words, the only dimensional data they put on the drawing are dimensions "critical" to the application. Any other manufacturing dimensions need to be interrogated from the model.
I just can't see that a corner fillet dimensioned to .25 MAX (to allow for any end mill to be used) is a critical dimension in a non-stress concentration application.
--Scott
http://wertel.eng.pro
RE: CRITICAL on drawings
RE: CRITICAL on drawings
--Scott
http://wertel.eng.pro
RE: CRITICAL on drawings
Chris
Systems Analyst, I.S.
SolidWorks 06 4.1/PDMWorks 06
AutoCAD 06
ctopher's home (updated 06-21-06)