Good drafting practices, GD &T, and culture shock
Good drafting practices, GD &T, and culture shock
(OP)
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,
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,





RE: Good drafting practices, GD &T, and culture shock
This model versus drawing discussion is driving me nuts too.
A lot of this depends on what kind of fabrication you do and what kind of tolerances you need to achieve. If you are 100% confident that ALL of your tolerances can be achived by an NC machine or by a casting or molding, you can rely completely on the CAD model.
Until then, I want my stuff to go out as a drawing, with tolerances. I want it to go out on paper or on PDF so that there is an exact image of what I saw on my computer screen. I am not 100% confident in DXF.
There is an ASME standard on 3D models, but I do not know how many shops and inspectors understand it, and have the tools to support it. I am also curious about how you would mark up your dimensioned 3D models with a highlighter as your check them or inspect the parts.
JHG
RE: Good drafting practices, GD &T, and culture shock
Obviously you need some drawings to specify material, datum points, revision level, tolerance and the like but complete manufacturing drawings?
As someone who also works in the automotive industry for many years now all we get are solid models and the very bare minimum of information, it works fine.
Unless this information is needed for manufacturing or inspection why create it? As far as I can see all you are doing is creating extra work, making the company less profitable and putting peoples jobs at risk, I know I would resist the changes you are trying to make.
I am sure other will see things differently.
RE: Good drafting practices, GD &T, and culture shock
Chris
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RE: Good drafting practices, GD &T, and culture shock
Sorry I can't help your argument on this point.
2) The most effective way to instill this discipline that I am familiar with is to have a knowledgeable, dedicated checker who is given the authority to reject poorly drawn drawings. Checking against applicable standards is his only function, and his word is law. While there will be much grumbling that the changes he requires may be unnecessary, in the long run the drafters (and designers) will thank him, as creating a proper drawing becomes second nature to them.
RE: Good drafting practices, GD &T, and culture shock
Chris
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RE: Good drafting practices, GD &T, and culture shock
I don't know mmakm's whole situation, so I wanted to give him a heads up on what's out there. Given that they don't yet follow Y14.5, I agree that they should start with the drawings.
RE: Good drafting practices, GD &T, and culture shock
This subject hits a nerve with me.
CAD and 3D modeling is a power tool. I wish it were used to it's full capacity. Unforunately its not in most cases.
Chris
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RE: Good drafting practices, GD &T, and culture shock
1. All though brought up and trained a certain way, I'm not at all interested imposing my beliefs, just influencing so that the solution makes sense. I'm not at all interested in creating extra work that doesn't provide value to the product.
2. 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.
3. We produce in relatively small volumes. Typical EAU is less than 1000 at most and typically in 100 to 300 range.
We had a checker at one point and just due to lack of incoming drawings to check, he was pulled in another direction.
I almost need to look at each part on case by case basis and take into account who the vendor is and thier capabilities. I think being a relatively small company with all business function ocurring in one location, that we have a tendency of taking standard practices forgranted.
RE: Good drafting practices, GD &T, and culture shock
While being in the opportunity you have to make policy for your company.
1. I would first investigate the successes and failures toward was going 3-D
2. I would look at the cost benifits of not producing paper. This alone can be enough of a saving to keep your company going to the overseas world for cad and design work
3. I would set up a pool of people (former checkers/draftsmen) to become model auditors. These people would be proficient in the use of the cad system to be able to know how to instruct the proper application of the required GD&T and tolerencing requirements. These people would have disciplinary power that if after a set amount of time some one was habbitually not following modeling best practices that these vio;ators would be disciplined after a gracious training/implementation period.
4. I would set up by a small group of software guru's and company product lead people as to what best modeling practices should be. Make a formal company standard of this that has pictorial examples and definitions of what is expected.
I worked for a company that was headed in this direction in most of the multiple facilities they have. It worked very well. It weeded the more unproffesional slugs out of the system as well. I am trying to emulate this type of phylosophy in my new one horse company that will soon be hiring others.
P. S. These points of thought may grow as I ponder what is being spoken about here
RE: Good drafting practices, GD &T, and culture shock
http://www.mattel.com/index.asp?f=true
Chris
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RE: Good drafting practices, GD &T, and culture shock
I agree with you, I feel like I've taken a step back in time. The questions is getting up with the times and how to drive that change. Training is definetly the answer but is not always feasible (for a number of reasons). First, to train I need funds. To get funds I need an argument. To support my argument, I need information on how this will impact the company. I'm sure its the same in alot of places... I've taken, as well as yourselves, the initiative to learn more about the topics that affect my career and industry, but I'm sorry to say, I've seen a large number that haven't or aren't interested. (Just a little ranting & raving, sorry) That becomes the hurdle.
RE: Good drafting practices, GD &T, and culture shock
Chris
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RE: Good drafting practices, GD &T, and culture shock
Many of our customers send us models and "reduced dimension" drawings that only specify tolerancing and other critical information. The model is regarded as the master definition. We do the same when outsourcing tooling. It has worked fine, so far.
Whichever path you decide on, good luck!
RE: Good drafting practices, GD &T, and culture shock
To imply that the technology will be in place some time in the near future is wrong, it is there now. For any body panels, facia or complex 3D formed parts the likes of BMW, Audi and Ford simply give a model and a very basic drawing. Everything can and is machined and measured to this, if you do not have the CAD software or the CMM and know how you do not become a first tier supplier, that is how they work now.
That does not mean that this is the best way for everything, if you want a 10mm steel bar saw cut to a length of +/- 5mm then a fag packet sketch and a steel tape is probably all you need, to spend ten of thousands on computer software and a CMM would be a waste and probably see you out of business.
In the same way a shaft with many diameters and shoulders that are highly toleranced is probably best drawn in 2D.
A highly complex 3D form is best modelled and in fact probably cannot be dimensioned or measured using 2D prints.
It all boils down to what you are trying to achieve.
RE: Good drafting practices, GD &T, and culture shock
Chris
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RE: Good drafting practices, GD &T, and culture shock
If it was one of my posts that you were refering to, I wasn't trying to imply that the technology isn't yet here, just that industry is very slow to accept it. I agree that if you want to be a prime supplier, you stay on the cutting edge.
It IS the practice with some of the aerospace giants, and we have recived packages where the only paper involved was the instructions on how to interpret the model. The only reason that was required was because the CAD software isn't yet fully complient.
I fully agree that there are some parts that just can't be fully defined on paper, short of having hundreds of cross sections. I work with these type parts everyday.
As you said, "It all boils down to what you are trying to achieve".
RE: Good drafting practices, GD &T, and culture shock
Someone here on eng-tips once wrote something along the lines of:
To do away with a proper drawing is to do away with source or incomming inspection. This is not a bad thing, if you know that all of the parts are good.
Step 1 is that you really have to know what you can accept.
Step 2 is that you really have to know the manufacturing process. Speciffically its limits of variation and repeatability, and that the process is, and will remain in control.
Step 3 is to inspect the hell out of a statistically significant number of "first articles", and calculate the distributions of all the dimensions.
Step 4 is to assess steps 1 through 3, and decide if the vendor has the ability to consistently produce parts that you will accept.
If you can get through steps 1 - 4 then you can have some degree of confidence that most of the parts will be good parts.
Repeat for all vendors.
RE: Good drafting practices, GD &T, and culture shock
Not necessarily. If your operation is set up with the correct software and training, you CAN inspect incoming parts relative to the model ONLY. ASME Y14.41 defines the standards for documenting the features and tolerances of the part sans any drawing.
RE: Good drafting practices, GD &T, and culture shock
Chris
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RE: Good drafting practices, GD &T, and culture shock
RE: Good drafting practices, GD &T, and culture shock
I am sure the same applies to airbus and Boeing.
RE: Good drafting practices, GD &T, and culture shock
Not necessarily. I've worked with/for Boeing, not always the case. Don't know about Airbus.
Chris
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RE: Good drafting practices, GD &T, and culture shock
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...
RE: Good drafting practices, GD &T, and culture shock
As long as your tolerance requirements do not exceed the capability of the inspection tools, you should be alright.
"Art without engineering is dreaming; Engineering without art is calculating."
Steven K. Roberts, Technomad
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RE: Good drafting practices, GD &T, and culture shock
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
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RE: Good drafting practices, GD &T, and culture shock
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
RE: Good drafting practices, GD &T, and culture shock
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.
RE: Good drafting practices, GD &T, and culture shock
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
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RE: Good drafting practices, GD &T, and culture shock
RE: Good drafting practices, GD &T, and culture shock
We've had that problem... A public execution of one offender put a stop to that practice.
RE: Good drafting practices, GD &T, and culture shock
My experience is you can have both, a detailed quality model that reflects best practice GTols...Phil
RE: Good drafting practices, GD &T, and culture shock
RE: Good drafting practices, GD &T, and culture shock
I agree 100% +/- 1%.
Another star for you.
Chris
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RE: Good drafting practices, GD &T, and culture shock
"... 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
RE: Good drafting practices, GD &T, and culture shock
RE: Good drafting practices, GD &T, and culture shock
RE: Good drafting practices, GD &T, and culture shock
RE: Good drafting practices, GD &T, and culture shock
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
RE: Good drafting practices, GD &T, and culture shock
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.
RE: Good drafting practices, GD &T, and culture shock
First I want to give a big 'heck yeah' to Kenat's comments. I also want to say that implementation of ISO 14.41 would be absolutely impossible with my company's suppliers given that several of them could maybe produce about 10 teeth per capita from their workforce but those suppliers give us the best PPM's of all our suppliers because they know what we need. They know how to read our drawings.
Don't forget to cite ANSI/ASME screw thread specifications on your drawings and/or purchase orders!! Does your inspection process measure minor diameter of internal threads or major diameter of external threads? Functional go-no/go pitch gages are relieved beyond maximum material condition and won't tell you if you have a wallowed out internal minor diameter resulting in a weak thread. Also, it's not a bad idea to let your suppliers know which ASME screw thread inspection system you are going to use to inspect their product. We use System 21 (actually the most lenient system) and have communicated that to our internal and external suppliers. Everyone knows precisely how we will inspect so that they can inspect their own work with the same inspection criteria.
Kenat- I'm doing the checking because nobody else will, but I'm pushing for a random 'peer review' system. Pray for me. ;>P
Regards -John
RE: Good drafting practices, GD &T, and culture shock
I threw my 2 denari worth in a thread a while back.
thread1103-151962 (12th June)
For starters I believe in 100% checking. In fact I prefer 300+% checking, ie there are 3 signatories in addition to the drafter/designer, my last place was aerospace/defense, every drawing be it new or an amendment got signed by Checker, Stress Engineer & Chief Engineer/Technical Director. While in theory the Checker was the only one doing a detail drawing check the others would spot things, especially our chief stress engineer.
First preference dedicated checker(s).
Second preference one designer designated as the primary checker (ie everyone else’s work goes through him, this is perhaps most applicable to small companies).
Third preference checking each others work (inexperienced staff should be excused from this duty except as learning experience)
Last, and a poor last is self check.
I don’t count design reviews as drawing check, they are good for the big picture but not much use at detail drawing check from my experience.
Just my opinion for what it’s worth. Drawing check is the best way to enforce standards/good practice that I can think of.
RE: Good drafting practices, GD &T, and culture shock
Good luck John, I'm not sure I agree with random peer checking (by this do you mean only some get checked at random or the checker is picked at random?) but something is better than nothing.
RE: Good drafting practices, GD &T, and culture shock
I 300% agree.
Chris
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RE: Good drafting practices, GD &T, and culture shock
I'm the QAE for a manufacturer of water pumps. There is a simple part we have made by a supplier for which there was never a drawing. It's a radiator cowling spacer for a John Deere diesel engine that powers several of our pumps. All the guy does is cut 7/16" schedule 80 pipe 1-1/4" long on a chop saw.
I mentioned to the design folks about a year and a half ago that there really should be a drawing for this part in case we ever gave it to someone else to make. 500 of these parts came in today and the inspector found the following: a drawing appeared out of nowhere sometime between the last delivery in May and today; the drawing date was 3/3/05; the drawing shows a length, 1.29 ± .01, that is not the length we need and has a tolerance that God couldn't hold on a chop saw; and a .41 ± .01 diameter on the ID that actually is the 7/16 pipe 'as bought'. The drawing has the name of the person who drew it, but no initials for the engineer or the checker.
I called the supplier to find out when he recieved the drawing. His answer was: "Yesterday."
Lord help me.
RE: Good drafting practices, GD &T, and culture shock
One time I created a detailed drawing of a part that fit into another a certain way. Made an assy to show the direction it goes. All were checked and signed off by checker/designer/eng/QA/mngmt.
Later, a new assy person decided the part should go in rotated 180deg. The aay person and the mfr eng marked-up the dwg, then had more parts made, then shipped them to the customer without any checking or approval. All parts and assy's were sent back from the customer. Thousands $$ were wasted.
So, not only do you need a checker, you need a good system in place to track all drawings from drawn to release through change.
Chris
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RE: Good drafting practices, GD &T, and culture shock
Why should the drawings be checked by a specialized checker? What should a design checker know that an experienced, reliable designer or engineer need not know?
I cannot think of a better background for a design checker than extensive design experience.
JHG
RE: Good drafting practices, GD &T, and culture shock
Chris
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RE: Good drafting practices, GD &T, and culture shock
In addition to what ctopher put:
Of course his background should be in design, I can't think of any other decent way to get the skills & knowledge required probably 10+ years preferably to defense/govt requirements. Doesn't mean his current primary role need be design.
Practice makes perfect, the more time spent checking the better you'll get at it. Dedicated checkers spend more time checking so get more practice.
Some people make great designers but not such good checkers. Every checker should be a reasonable designer but not every designer is or need be a particularly good checker. Not just from a technical point of view but from a personality point of view.
Putting all drawings through a single person or small group better ensures consistency in interpretation of standards etc so leading to a common level of drawing quality.
I could probably go on about this for a while. I've worked under all the ways of checking I listed in my previous post except for the self check (I always check my work before submittal to checking but almost always miss something). From my experience and talking to other experienced colleagues independent dedicating checking is best.
If other designers are to do the checking then it should be ensured that they are adequately qualified/experienced. IMHO takes more experience to be a good checker than to be a good designer.
RE: Good drafting practices, GD &T, and culture shock
As for self checking, unless you set the drawing aside for a week or so, most of the mistakes will be invisible to you. Even then, it is much easier to miss your own mistakes than someone else's.
RE: Good drafting practices, GD &T, and culture shock
You can make your argument, but don't lose your job or get in trouble with it. I would be hard pressed to send a 3D model out to a vendor for fabrication instead of a 2d drawing. One of the problems you may be facing is the company's attitude towards drafting as being the last rung on a ladder compared to engineering. I have my drafting, design and engineering degrees and I can tell you countless times where engineers themselves are horrible drafter and refuse to do it all together because its beneath them.
If you feel like you fighting an up hill battle then you might want to call some out side ISO consultate to explain to the managment the improtance of drawing or find a new job.
RE: Good drafting practices, GD &T, and culture shock
so when i send stuff out for vendors i ask them what they want to build off of. cause there is a good chance i already have what they want. so to answer the root question
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?
Tell them "the FDA will come hunt you down, eat you and swallow you whole with out even taking a breath." luckyly i was the new guy and i told them im trying to make things right, and they let me go.
RE: Good drafting practices, GD &T, and culture shock
Take a look at ASME Y14.41 and see where the future is headed. MBD doesn't mean that you have to completely do away with drawings, just that the drawings don't have to contain every bit of information required to make the part when your model already contains that information.