Good drafting practices, GD &T, and culture shock 12

[mmakm]

Hi all, I'm a lead engineer for a medical device manufacture that has a long history in the automotive and consumer products industry. I have a good background and understanding of GD&T and have been through many coarses. With that being said, the company I'm currently with does not practice GD&T and does not have good drafting standards & many untrained designers (Untrained in good drafting proactices). I'm making an attempt to create standards based on ANSI Y14.5.1 and also instill good drafitng practices in the designers. The questions and issues I have are these:

1. I'm trying to make a good arguement for complete manufacturing drawings because I'm constantly getting resistance to this because we supply 3d cad data and the parts are typically produced from this data. Other than incoming inspection, if the parts fits, the drawing rarely gets looked at. What are other arguements?

2. Does anyone have a good approach to driving GD&T and good drafting practices into a culture?

I was going to add more but if I could get some resolution to these issues, we've taken a huge step. Any input is appreciated, & based on what I've read in these forums we have a great knowledge base.

Thanks,

 

[ewh]

I didn't say it would be easy.

 

[ajack1]

Not difficult at all, all you need to be is one of the top three or four automotive manufactures in the world and say if you want my work, you play by my rules.

I am sure the same applies to airbus and Boeing.

 

[ctopher]

ajack1,
Not necessarily. I've worked with/for Boeing, not always the case. Don't know about Airbus.

Chris
Systems Analyst, I.S.
SolidWorks/PDMWorks 05
AutoCAD 06
ctopher's home site (updated 06-21-05)
FAQ559-1100
FAQ559-716

 

[wes616]

I work for a t1 interiors manufacturer for AB, and guess what... most of our engineers are to scared to switch to 3D... airbus doesn't care, because the accept our drawings, and we manufacture install and inspect our own components with AB oversite. (we are the last stop before the a/c is delivered to the buyer.

Here is a horrible example... another program group here, will model parts in 3D then dump them out as 2D line entities so they can dim and annotate in autocad... it's a little scary.

Unfortunately with no MANDATE to switch, this place will not... that god i'm a contractor! and in the product team that is working (almost) exclusivly in 3D.



Wes C.
------------------------------
When they broke open molecules, they found they were only stuffed with atoms. But when they broke open atoms, they found them stuffed with explosions...

 

[MadMango]

I worked in the medical device field, and that company used the 3D model as the master document. Model files were sent to the suppliers of our injection molded components. Incomming parts were inspected on a CMM, and used a Quality Control drawing that listed inspection dimensions, criteria, and what inspection tools were to be used.

Its kind of comical but sad. We can call out all the dims we want, all day long, but other than a set of calipers, mics and a height gage, we don't have any inspection equipment.

As long as your tolerance requirements do not exceed the capability of the inspection tools, you should be alright.

[green]"Art without engineering is dreaming; Engineering without art is calculating."[/green]
Steven K. Roberts, Technomad
Have you read faq731-376 to make the best use of Eng-Tips Forums?

 

[Heckler]

Here is a horrible example... another program group here, will model parts in 3D then dump them out as 2D line entities so they can dim and annotate in autocad... it's a little scary.

We have a designer that likes to do this. I can't tell you how many times I've made him redoe drawings in the 3D program. I'm constantly telling him that SolidWorks is our primary design tool and A-CAD is used for legacy data.

Best Regards,

Heckler
Sr. Mechanical Engineer
SW2005 SP 5.0 & Pro/E 2001
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o
_`\(,_
(_)/ (_)

Never argue with an idiot. They'll bring you down to their level and beat you with experience every time.

 

[Tunalover]

I use GD&T to make tolerances as loose as possible while insuring the functional requirements. This normally means more symbols on the drawing.

As a rough estimate, I'd say that 1% to 6% of shop people who read drawings actually understand what those symbols mean. I've had times when vendors charged me more for parts that had MUCH looser tolerances only because the drawing had more "fancy symbols" on it.

It's been a hard sell over the years. I eventually learned to clam up on the subject and just use the method whenever I can get away with it.


Tunalover

 

[aardvarkdw]

One thing I am curious about after reading the posts in the this thread is, what about doc control? How do companies that only produce 3d models keep track of revs?

We have a few parts that make up the outer enclosures for some of our machines that have complex shapes and our "drawings" essentially consist of top and side veiw of the part and a note saying build from .sat file. Our problem has been that the file has gotten corrupted, a change has been made, or what happens most of the time, an engineer gets ahold of the model and breaks constraints and sketches. Now we have no idea how to rebuild what we had.

Do people just make a copy of the model everytime a rev change is made? I would like to see our company do away with drawings but I just don't see how we could with our current doc control.

 

[ctopher]

aardvarkdw,
For SolidWorks and ACAD, I use PDMWorks. It shows the rev's for all parts, assy's and dwgs. Then each dwg is saved as PDF for each discipline and vendors to work from.

Chris
Systems Analyst, I.S.
SolidWorks/PDMWorks 05
AutoCAD 06
ctopher's home site (updated 06-21-05)
FAQ559-1100
FAQ559-716

 

[ewh]

We place released files in a protected directory in which no one has any write access to them, with the revision as part of the file name. When they are revised, they have to be renamed.

 

[wgchere]

or what happens most of the time, an engineer gets ahold of the model and breaks constraints and sketches. Now we have no idea how to rebuild what we had.

We've had that problem... A public execution of one offender put a stop to that practice. Sometimes you just have to draw a line in the concrete. Before it sets and you toss the guy in the river!

 

[plariviere]

Save yourself a lot of discussion. This subject is old to me. I have been a dimensionless drawing supporter for over 10 years. I have seen nothing but success, when aligned with good vendors. ASME Y14.5 is also available in a very useful specification detailed for model space application or model space with limited drawing format. Look for ASME Y14.41-2003. It is an excellant reference for this debate.
My experience is you can have both, a detailed quality model that reflects best practice GTols...Phil

 

[ewh]

See my post of 8Apr06. Y14.41 is a good reference. Y14.5 should be used in conjunction with Y14.41. The key is having everyone involved buy in to both standards.

 

[ctopher]

ewh,
I agree 100% +/- 1%.
Another star for you.

Chris
Systems Analyst, I.S.
SolidWorks/PDMWorks 05
AutoCAD 06
ctopher's home site (updated 06-21-05)
FAQ559-1100
FAQ559-716

 

[drawoh]

aardvarkdw,

"... Our problem has been that the file has gotten corrupted, a change has been made, or what happens most of the time, an engineer gets ahold of the model and breaks constraints and sketches. Now we have no idea how to rebuild what we had."

I see two issues here, neither of which have anything to do with GD&T. The first is that you do not change form, fit or function of existing production parts. The only difference between old fashioned paper drawings and 3D models is that 3D CAD will model the screw-up you have caused if you do change something.

A lot of people have told me that 3D CAD is easy and user friendly. Maybe the software is. The 3D models require good practise by the designer. Sloppy, disorganized designers can create far more havoc now than they could back the days of drafting boards.

If you are in an organization that is determined to hire low-cost, marginally compentent people, you are going to have problems with 3D models, and problems with clear communications to fabricators, GD&T or no GD&T.

JHG

 

[ktlasers]

Work from the top down. And you know what people at the top think about...money. Here's the website for a Honeywell guy who could tell you about saving money with GD&T:

http://www.gdtpcertification.com.

Seriously, if your top guys/customers know how much incomplete drawings are costing them, they'll enforce education and certification.

 

[wgchere]

A star for the link. What a great resource--I'll have to get to studying this.

 

[ktlasers]

Thank you. Tom is an awesome teacher!

 

[JohnNabors]

Mmakim-

I don't know how much variety you have in the parts you are manufacturing, but I did something in my last job where we had parts that tended to have a limited variety of geometric features and applicatons of those features. I wrote a manual that was maybe 22 pages long covering each of the symbols and applications that we used in that plant and absolutely nothing else. I named it Common Sense GD&T. I used practical examples (for instance: some folks were confusing flatness with levelness, so the manual explained, 'When thinking of the difference between flatness and levelness, think of a pool table - when you saw the legs off one end, it's not level any more but it is still flat'). That made GD&T much less intimidating for CNC operators that had come to the company from places like Wal Mart and Circle K and helped tremendously in getting buy-in.

At the end of the manual I wrote, "Anyone wishing to learn more about GD&T may obtain a copy of the standard" from myself or their supervisor. A surprising number of them took me up on it.

-John

 

[KENAT]

mmkam,

I'm in a similar situation to you (can't believe I didn't notice this thread before) but my group has actually been tasked with introducing standards for commonality and to improve the quality of design documentation (primarily drawngs).

We're introducing company standards which reference the ASME/ANSI standards but also amplify certain points or where there is scope for variation in the standard we will spell out our preffered option. We're trying to get people to buy into this and the benefits it will provide but some people are a hard sell.

Our main plan for enforcement is that eventually we want all drawings to go through forma checking by dedicated checkers. We're not there yet but give us time!

Although we do provide the vendors with models when requested we continue to use 2D drawings as the primary part definition. There are a number of reasons for this a major one is that as I understand it (haven't managed to get the spec yet) for MBD per 14.41 to work you'd have to be able to supply the vendor with annotated models. This requires a file format your vendor can read. We don't have high enough turnover to force any vendors to obtain compatible software (including something like JT). So we stick with 2D which we can print out hard copy or PDF.