What, if any, is today's "Industry standard" and/or "best practice" for creating
What, if any, is today's "Industry standard" and/or "best practice" for creating
(OP)
Hello Colleagues ~ I work for a fairly large and diverse International company and have been “tasked” with implementing a “GLOBAL” 3D NX design standard to include the logic that “ALL parts are to be modeled to mid-range of tolerance”. Not a problem here in the USA, that’s how I was taught. However, it seems my European colleagues are NOT in agreement with this at all. Please help me to better understand their “rational” behind this. Thank you.





RE: What, if any, is today's "Industry standard" and/or "best practice" for creating
.2500 +.0000/-.0004 would be modeled at .2500 if you were to model it to the nominal. Not .2498.
Some machine operators/programmers prefer drawing/programming to the MEDIAN of the tolerance, which would be .2498. This allows for equal deviation from the 'starting point' of manufacturing operations.
Just wanted to clarify your starting point since you seemed to equate nominal with mid-range of tolerance.
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NX8.0, Solidworks 2014, AutoCAD, Enovia V5
RE: What, if any, is today's "Industry standard" and/or "best practice" for creating
Instead they'll start with the nominal hole/shaft size and may have double negative or double positive tolerances e.g 12 mm nominal +.1 +.5 or some such meaning the part could be between 12.1 & 12.5 mm.
Also from a tolerancing point of view 'min' and 'max' are valid - how do you model that at nominal?
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: What, if any, is today's "Industry standard" and/or "best practice" for creating
RE: What, if any, is today's "Industry standard" and/or "best practice" for creating
"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future
RE: What, if any, is today's "Industry standard" and/or "best practice" for creating
Then I do not believe you are as standard as you believe. Design/Engineering models, in my experience, model to the "nominal" even if it is an unacceptable value in manufacturing. For example 1.5000" g5 (-.0003/-.0007)(ANSI B4.1 limits and fits). This is pretty common in the manufacturing world in the USA. It will be modeled at 1.5000" but woe on the programmer/machinist that cuts it to that size without reading the print. Which brings me to my next point:
I've only been in environments that push for the MEDIAN when they were machinists actually making parts. That, to them, is the "safe" place to start. It's also a lazy approach. I would say it's also a somewhat inexperienced approach, since you can change tool offsets if you're afraid of going too far past LMC/LMB on the first run.
So why do /you/ model to the MEDIAN? To me, that's extra work and more prone to human error as opposed to simply modeling to the nominal.
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NX8.0, Solidworks 2014, AutoCAD, Enovia V5
RE: What, if any, is today's "Industry standard" and/or "best practice" for creating
If dim is .2500 +.0000/-.0004, then model at .2500.
If dim is .2496/.2500, then model at .2498.
Chris, CSWA
SolidWorks '15
SolidWorks Legion
RE: What, if any, is today's "Industry standard" and/or "best practice" for creating
However, even if you ignore the 'standard limits & fits' aspect, there are other things. For instance drill sizes and resultant hole tolerances are often toleranced per the old Navy spec that ends up with +.005-.001 inch or similar. Also as I said, Min & Max are valid dimension schemes that are tricky to truly capture just with model geometry.
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: What, if any, is today's "Industry standard" and/or "best practice" for creating
I model my parts in SolidWorks to nominal size. This suits machined and sheet metal parts, which is what I do. I like to use the ANSI/ISO fits and tolerances. This is easy when I model to nominal. Median size makes complete sense when your parts are being cast, forged, rapid prototyped, or otherwise fabricated directly from the model.
How does your company document and fabricate stuff?
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JHG
RE: What, if any, is today's "Industry standard" and/or "best practice" for creating
Shrinkage in castings and material expansion from heat treatment (due to shift in crystal structure) pose opposing requirements.
It seems like hiring some manufacturing engineers to customize derived models to be in line with specific manufacturing technology would be the best option and let the drawings and models do what they do best, communicate between engineers and Quality Assurance.
Kenat - I'm not sure where the Navy got their values (AND10387?), but the Machinery's Handbook stated the sizes of resulting holes in their tables was determined by drilling 1000 holes in either cast iron or steel with fresh drills and that actual performance will be different. Having see people try to drill room-temp rubber, I can certainly agree.
RE: What, if any, is today's "Industry standard" and/or "best practice" for creating
Ask your CAD vendor when/how they'll come up to speed on tolerances.
Mike Halloran
Pembroke Pines, FL, USA
RE: What, if any, is today's "Industry standard" and/or "best practice" for creating
RE: What, if any, is today's "Industry standard" and/or "best practice" for creating
PTC parametrics does capture most of the tolerances. Actually, when it was paired with VSA it did even more.
It is possible to go through the model and select dimensions to be nominal, minimum, or maximum for those dimensions with direct tolerances and regenerating the model will produce representative geometry, but it falls short for tolerances applied by FCFs. At least in the VSA arena those tolerances were accessible and the VSA software could make alterations to a mathematical representation of the varied geometry.
However, none of this helps because manufacturing methods require further alterations. For example, the model that is required for injection molding needs to be scaled up by varying ratios based on the plastic characteristics; a similar requirement exists for making patterns for sand casting. I cannot imagine any universal system addressing this, though I've had over 30 years of making CAD 3D models, many of which were taken for manufacturing use.
Then one runs into parts that have extra material for processing that must be removed afterwards, like formed tubes where the bend ends too close to the nominal end. Extra material to support the bending can be trimmed after, but it would not be a normal part of the model.
RE: What, if any, is today's "Industry standard" and/or "best practice" for creating
However, for those of us outside of that environment there are still more questions than answers.
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: What, if any, is today's "Industry standard" and/or "best practice" for creating
I believe someone in your company does not have a clue what he is asking you to do. The world wide standard for manufacturing is laid out by ISO. ANSI is part of it. Get to know ISO 286. If you are a world wide company than that is the ONLY standard that is accepted world wide.
RE: What, if any, is today's "Industry standard" and/or "best practice" for creating
I don't recall 14.41 specifying a distinct CAD data format from which one could create a translator of all 14.41 compliant models and I don't recall them specifying a single interface for 'interrogating' the model so that everyone approaching the CAD data would have the same steps to get the same information.
Basically it translates what people used to do with 2D CAD drawing and adds some things that they thing would make it easier, but as it is all things to all users, it is nothing to anyone in particular. The only other thing it does is support oblique projections of text and notations.
MIL-STD-31000 is probably better, but only by a fraction. If I had to guess, I think 14.41 was driven more by Seimens and 31000 by PTC, but it's been a while so it's worth checking. For example, in 31000 is "The TDP format will be clearly stated in the SOW with an understanding of how lifecycle maintenance of the TDP will be performed. When specifying the TDP format, it is important to provide sufficient technical detail—for example, Creo 1.0 (native CAD with version number), STEP AP 203 E2, 3D PDF with PRC (ISO 14739), or other unambiguous electronic format specifications. Other format details should be provided as required in A.3.2.8 Block 8. Applicability of Standards—for example, specifying ASME Y14.5 and ASME Y14.41 for fully annotated 3D models."
**
An annotation is metadata (e.g. a comment, explanation, presentational markup) attached to text, image, or other data. Often annotations refer to a specific part of the original data. https://en.wikipedia.org/wiki/Annotation
1. a critical or explanatory note or body of notes added to a text. http://dictionary.reference.com/browse/annotation
RE: What, if any, is today's "Industry standard" and/or "best practice" for creating
Manufacturing Systems"
RE: What, if any, is today's "Industry standard" and/or "best practice" for creating
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: What, if any, is today's "Industry standard" and/or "best practice" for creating
The only reason not to model to the NOMINAL dimension is, as we have all discussed, for manufacturing purposes.
To me, (call it JN 101.1 ;) ), the solution to this is that there is an Engineering/Design Model separate from a Manufacturing/Programming Model. Or if it must be in the same model in-house, put some modeling features on a separate layer compliant with a company standard. Have the nominal model as the base of things. Have your "additional thickness for machining" and "scaled by .99965 to account for growth in oven" type modifiers on a separate layer. Leave the modified manufacturing models to the manufacturers. Ensure proper revision control and have a separate model for programming/machining than you do for the engineering model which needs the nominals to drive the proper dimensions, tolerances, annotation, etc.
If you decide to have separate models, then it's completely appropriate to ask which standard you adhere to for the Engineering Models/Documents, and then most likely you would use company standards for the manufacturing methods/models/modifications.
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NX8.0, Solidworks 2014, AutoCAD, Enovia V5
RE: What, if any, is today's "Industry standard" and/or "best practice" for creating
Imagine that we have "GLOBAL" design standard to keep our clearance holes to H14.
We model all the holes to the median.
Then some overzealous engineer decides to change it to H12.
Now we have to go back and re-model every hole to another median.
I don't see it happening. The only sane way I see is to model everything to BASIC.
Because when you have your nominal and your tolerance you can do anything you want, including creating separate model for manufacturing purpose.
And when all you have is model where everything is modeled to some bastard "median" - good luck! Especially after you convert this model to STEP and send to China.
"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future
RE: What, if any, is today's "Industry standard" and/or "best practice" for creating
RTFD, people!
RE: What, if any, is today's "Industry standard" and/or "best practice" for creating
RE: What, if any, is today's "Industry standard" and/or "best practice" for creating
Things like this indicate to me that the cradle-to-grave concept is not yet a general purpose solution. The only people I've barely gotten to discuss their no-drawing operations seem to depend on previously negotiated expectations for results based on information that is usually depicted on the drawing, such as tolerances. This seems to happen between companies that have done similar work before, such as for mold suppliers.
I expect that unless it is a high volume exchange of very similar designs, the process has a lot of e-mails and group phone calls.
RE: What, if any, is today's "Industry standard" and/or "best practice" for creating
Stinkin' PHD's....
Proud Member of the Reality-Based Community..
To the Toolmaker, your nice little cartoon drawing of your glass looks cool, but your solid model sucks. Do you want me to fix it, or are you going to take all week to get it back to me so I can get some work done?
RE: What, if any, is today's "Industry standard" and/or "best practice" for creating
If there isn't already, there should be a law stating: "The longer a discussion continues, the probability of an xkcd comic becoming relevant approaches 1"
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NX8.0, Solidworks 2014, AutoCAD, Enovia V5
RE: What, if any, is today's "Industry standard" and/or "best practice" for creating
The model-based-enterprise group wasn't even working on a new standard; just trying to put other standards into practice - That's how bad the situation seems to be. It's as if, in general, MBE is toxic even to motivated people who are just trying to eliminate drawings, much less automate conversions based on context.
Ever see how an ant-lion works>? MBE is like that, and engineers are the ants. Management looks and sees that drawings cost money and so to save money says - let's get rid of drawings. Then they see that downstream users struggle with models and say - let's make engineers create universal models. Then costs go up, so they get rid of engineers to trim costs and bring in cheaper (newgrad or contactors) engineers who aren't as good, but may seem fast. Then no one can use the models. Meanwhile, although these models are the core of operation for the company, none of the managers can be bothered to learn the software to examine the models nor are they interested in taking several hours every week to review the models because that costs money.
RE: What, if any, is today's "Industry standard" and/or "best practice" for creating
A quick search of 'Model Based Definition' in just this forum shows up numerous posts that may touch on this e.g.
thread1103-316370: Goal R.002 *Pulls hair out!*
thread1103-239768: Current state of Model Based Definition
thread1103-262305: Contolling Electronic Cad Data
thread1103-182500: Detailing Complex Geometry
http://www.eng-tips.com/search.cfm?pid=1103&ac...
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: What, if any, is today's "Industry standard" and/or "best practice" for creating
On "Current State of Model Based Definition," how did it turn out? It was sadly expected to see management inserting themselves in to a technical decision with little technical background. At this point it seems like a murder mystery with the last pages torn out.
The "Pulls hair out" is also interesting. If anyone wishes to follow this spark, please start a new thread, but whenever I gave a nominal value it was for the purpose of easiy comparison between features on other parts and not having to do with producing some 'target.' Essentially, the expected distribution was not Gaussian with the peak sitting on the nominal, but constant; every value in the range had the same probability of occurring.
So the +/+ and -/- make sense when it is more important to quickly realize the relationship between features on mating parts and not as a guide to a desired size distribution. For the purposes of MBD that would continue to be the case. While I didn't take it to an extreme, one might put dia 0.375 +.030/+.015 and make it clear that this is a clearance value of a dia 0.375 fastener rather than depending on knowing what the next larger nominal fractional drill size that was typically chosen to clear a 0.375 fastener. However in MBD that could be a problem as the acceptable range for the hole would not encompass the size of the surface representing that hole in the CAD model.
RE: What, if any, is today's "Industry standard" and/or "best practice" for creating
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NX8.0, Solidworks 2014, AutoCAD, Enovia V5
RE: What, if any, is today's "Industry standard" and/or "best practice" for creating
I think I whined about this in another recent thread but maybe didn't accentuate the MBD portion. http://www.eng-tips.com/viewthread.cfm?qid=385291
JNieman, I'm sorry but in some circumstances not having the model suite going straight into CAD/CAM can be perceived as a problem. For those of us in sectors where management is focused on chasing this quarters $ and maximizing share value....
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: What, if any, is today's "Industry standard" and/or "best practice" for creating
However, there at least 3 places off the top of my head where a programmer or machinist can compensate/offset the cutting tool or path to account for a modeled feature outside the acceptable range. This isn't even an exceptional situation. This is just every day stuff for CAM software and machine programming. There's a reason "offsets" are a pretty bog-standard thing.
Even if your model is 100% to "median" you will still use offsets in your day-to-day programming when you have situations where you have a different toolpath for 'roughing' than 'finishing' as your roughing pass will want to stop short of the modeled position.
If someone is really looking into changing the whole way /intelligent/ models are being made, to try and make them idiot proof, then they need to stop hiring idiots. There is no gain I can think of in requiring models to be made to the -median-. The "problem" that policy "solves" is more elegantly, efficiently, and intelligently handled using settings in the CAM software. Whether or not the model is outside acceptable range or to the media, the programmer still has to go through the same number of steps to generate their outputs. The tolerance can dictate operation settings: tool selection, tool settings, cutting strategy, number of finishing passes, etc.
I don't know - I've been on every side of it. Design, Drafting, Programming, Quality... it's just never been a problem or a hurdle that caused preventable labor. I'm not saying it's a topic immune to "seagull manager input" but it's not a /real/ problem in my mind.
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NX8.0, Solidworks 2014, AutoCAD, Enovia V5
RE: What, if any, is today's "Industry standard" and/or "best practice" for creating
A star for you.
Chris, CSWA
SolidWorks '15
SolidWorks Legion
RE: What, if any, is today's "Industry standard" and/or "best practice" for creating
John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
Digital Factory
Cypress, CA
Siemens PLM:
UG/NX Museum:
To an Engineer, the glass is twice as big as it needs to be.
RE: What, if any, is today's "Industry standard" and/or "best practice" for creating
As an inspector, no number is any better than any other number. There is good and bad, go or no-go, black and white.
As a button-pusher, they may shoot for the median to make their life easier, or shoot toward LMC so they don't have to change their tools as they wear, as often, so they can boost their production numbers.
As a machinist worth their salt, they will look at the purpose of the part and do their best to make the best part they can, including consideration for fits, datums, and other functional surfaces/components/holes.
Depends on what seat you're in.
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NX8.0, Solidworks 2014, AutoCAD, Enovia V5
RE: What, if any, is today's "Industry standard" and/or "best practice" for creating
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NX8.0, Solidworks 2014, AutoCAD, Enovia V5
RE: What, if any, is today's "Industry standard" and/or "best practice" for creating
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: What, if any, is today's "Industry standard" and/or "best practice" for creating
Your tolerance range is the range of dimensions you will accept from the fabricator. The shop's job is to do this as cheaply as possible. They will exploit your tolerances to accomplish this.
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JHG
RE: What, if any, is today's "Industry standard" and/or "best practice" for creating
There are a bunch of scenarios here.
Possibly, the fabricator's process is marginally able to achieve your tolerance. When he gets inside it, he is done, and he is darn glad! The as fabricated dimension winds up where it winds up.
Example
Routinely, I specify holes as something like Ø5/4.2mm at zero positional error at MMC. Note how there is no possibility that I will get a Ø4.2mm hole. The fabricator will open the hole up enough to give himself a manageable positional tolerance. Let's pretend that the fabricator can do a Ø0.2 positional tolerance. That allows for Ø4.4mm hole. Is that perfect for me? Do I want the largest possible contact area for my fastener head, or do I want a bit of allowance in case the mating part is not to specification? Maybe the best thing is for neither of us to push any envelopes.
The fabricator's job is to manufacture pieces to my drawings. I do not send them my assembly drawings. Often, I don't want them to know how the parts will be used.
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JHG
RE: What, if any, is today's "Industry standard" and/or "best practice" for creating
If so.. yea, I've done that when they were close enough and knew we making the parts work as-is was cheaper/faster than remaking the part. There's the option for the manufacturer to ask engineering for a one-time allowable non-conformance or deviation or whatever you wish to call it.
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NX8.0, Solidworks 2014, AutoCAD, Enovia V5
RE: What, if any, is today's "Industry standard" and/or "best practice" for creating
Please note that you can now edit (as well as delete), for a period of 24 hours, any of your OWN posts, so you could have gone back and added the additional text. After posting a response and you discover something that you wish to correct, just look for the 'Edit' and 'Delete' options in the lower Right corner of your post, as shown below:
Note that this is a new feature added to Eng-Tips in the past week or so. But note that there will be a 'paper trail' showing what it is that you edited so you can't use this tool to 'rewrite history' as it were.
John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
Digital Factory
Cypress, CA
Siemens PLM:
UG/NX Museum:
To an Engineer, the glass is twice as big as it needs to be.