Dimensioning Philosophy

[dr_gallup]

Just another data point from someone who has been around the block...

Form, fit & function are too critical to stop even at the part model, let alone the drawing. In almost all cases, assembly fit must be verified at multiple levels. Since we modify our parts in part or assembly mode anyway, allowing the drawing to drive the model really adds little value.

I find that using the model dimensions in the drawing makes it much easier to verify the fit in the assembly. How else can you do tolerance analysis? If your part model says the tol is .001 but the drawing has a created dim with .010 tol you are going to be making a big mistake. If your part dimensions scheme comes from one end but the drawing dimension scheme is from the other, mistake again. Most people I know go about making tons of dimensions with tols turned off during feature creation, the tolerances don't even get displayed until the drawing is made. For me there is a lot of value in using part dimensions, if it doesn't work in your industry, do what works for you. For the people with really complex surfaces, I don't know how you dimension or inspect those things. If you have to use laser scanners to check your surfaces then it probably makes sense to just work from the model and have only a few key dimensions on the drawing.

 

[Brian_Adkins]

Gallup.


I think you may havemisread my posting. Our part drawings are critical (that's how the parts get built). The point I was making is that changing dims directly in the Pro/E model is not a big benefit for us (I actually wish we could turn that bidirectional associativity off sometimes). Shown dims only have a benefit to me (that's $ for me) when they take less time than Created dim and the drawings get done faster.


Also, I was trying topoint out that one of the most-often purported benefits of modifying driving dims on drawings is that you can open the drawing, change a dim, renegerate, save your work, and poof, you're finished. This was how many Pro/E AE demos I watched back in the early 90's went. This, of course, is only true if you're designing parts that don't need to interact with other parts... Once you start pulling up assemblies to beginverifying Form/Fit/Function of the modified part, that 'benefit' disappears pretty quickly in my experience.


...but like you said, do what works for you (probably good advice for everyone on this thread...and not just on this topic).

 

[pmack009]

I think we are all on the same page on this. I just see some people trying to force show dim's when there are good reasons not to. Dr. Gallup hope you don't take my comment to heart you are a big contributor to this form<?:namespace prefix = o ns = "urn:schemas-microsoft-comfficeffice" />

 

[dr_gallup]

Don't worry about offending me, I have a pretty thick skin. But I am constantly amazed at how quickly differences in opinion degenerate into name calling and flame wars on the web. Actually, this site is pretty civil compared to most!

 

[scottm]

I spend a lot of time on "professional" contractor forums (like landscapers, etc.) to glean feedback on products. Seeing an argument over dimensioning (overly heated though it may be) is refreshingly professional.


I didn't see any, "Well if any *** shows up on my doorstep trying to make me SHOW dimensions, than he better be ready for my shotgun".

See how much worse it could be?





That said, it might be a frequent debate, but it was informative for me.
Edited by: scottm

 

[TeamMizuno]

BigJoe's friend here. Thought I'd chime in with my rebuttal to
dr_gallup as most of the users here seem to be newbies torn between 2
ways of modeling.

Boy does this guy have anger management issues!

Thanks for the psycho-analysis. I hope I can make it thru this rebuttal before I put my foot thru my monitor.

I've designed fuel injection systems that are running all around
the world in BMWs, Jags, SAABs, Vettes, etc. Safety & emmissions
critical components, not pastel cell phones.

I might've designed that pastel cell phone you own, but I've also
worked for some very prominent medical device companies...one of which
sells their product (blood glucose meter) to both hospitals and
consumers. I know what it is to deal with safety and the
FDA. But thanks for insinuating otherwise to try and boost your
argument.

Obviously he has never worked in the automotive industry.
Drawings and specifications are the only deliverables a design engineer
produces and are legal contracts. Screw it up & your company could
be sued or worse, people die. All the part definition between our
company, suppliers and customers is in drawings or specs. Only the
plastic parts get sent as CAD files, but there are still detailed
drawings with every dimension necessary to create the part supplied.

Well, if you screw up a drawing, maybe you shouldn't be designing
the part in the first place. Your comment is nothing more than
trying to instill FUD (fear, uncertainty, doubt).



No one is saying that you don't dimension the drawing with
design intent. This is true for any CAD package.
This should not inhibit doing tolerance analysis whatsoever. This
also does not make the product less safe. Afterall, a
part/product goes thru first article inspection and subsequent
inspections if needed until the tool is approved, parts go thru
reliability testing, production parameters are adjusted and controlled,
etc. before a part is ever released to production. After
production is ramped up and running, incoming inspection and audits on
production tools ensure the part meets its spec. Regardless, I
don't see how somebody could die from not using "show dims"...which is
the true topic here. Insinuating that it's somehow safer by
modeling with design intent is laughable.



So with the above comments, I'll state why I don't like to use "show dims":



1. It forces you to go to the model to change it. This is
the best way to avoid conflicts, especially if the part interacts with
other parts. And this is the only way if the features being
changed are based off of a master model. Just because you can
move a rib in a drawing does not mean your job is done. You
should now that you're not causing problems (e.g. interference) with
another part or if you're moving other features on accident. The
best way to avoid this is to be able to see all of the dimensions used
to create the feature as well as how it was created...in the model.



2. Design intent can change during the design cycle. ID can
change, mating conditions can change, etc. You want maximum
flexiblility for change. Locking yourself down with design intent
does not constitute flexibility. And things always change...a
button moves here, a jack moves there, a surface completely changes,
etc.



3. It is highly unlikely to have your drawings exclusively using
"show dims". Most of the time you will have to create some
dims. Mixing show and create dims just makes things more
confusing.



4. It is a waste of time...both during creation and, if
necessary, having to redefine the model if the design intent
changes. I'll give an example...suppose you create a rib in a
plastic part. Then you add draft. Now you go into the
drawing and hit "show dim". The rib cross section looks like
this: \__/ and you notice the dimension is minus draft and you
wanted plus draft. Well, you'd have to go back and redefine the
draft. Now you want that rib to be based off of a different
feature. Again, you wasted time thinking of the original design
intent and now have to go back and redefine it instead of just creating
a dim and being done with it.



So in conclusion, go ahead and waste your time if you desire using
"show dims" but please don't insinuate that there is any benefit that outweighs the negatives.
Afterall, plenty of CAD packages don't have "show dims" and people
still do fine.



Cheerio!










Edited by: TeamMizuno

 

[BigJoe]

That's the reply I was waiting for. Thanks for posting, TeamMizuno.

3. It is highly unlikely to have your drawings exclusively using
"show dims". Most of the time you will have to create some
dims. Mixing show and create dims just makes things more
confusing.

IMO, this is the strongest part of your argument.





-TeamNike

 

[scottm]

I'm not sure if I think its confusing, but I can understand the time argument. I have yet to decide if there is an inherent value in a shown dim, as the created dims are "attached" to the model as well. Obviously you don't think there is.

 

[AHA-D]

The only advantage I see is that tolerances get their way back to the model.


Or to explain further :


When you make a design you're most concerned with getting the geometry right. So choosing nominal values that "will work" is the first step. Once in drawing level most of these dimensions need to be toleranced. When these dimensions are shown dims then adding values for tolerances is reflected back to the model whereas the same thing is not true for created dims. When getting back to the model this adds an advantage of being able to check fitting inside an assembly without going back to the drawing.


Note : when you're a "clean" designer - making use of all the features, and not trying to press all geometry into one uncomprehendable profile - then show dims will work. If not you could end up taking more time to clean up the mess of dimensions all across theview then if you would create them one by one.


Alex

 

[dr_gallup]

That's the reply I was waiting for. Thanks for posting, TeamMizuno.

3. It is highly unlikely to have your drawings exclusively using
"show dims". Most of the time you will have to create some
dims. Mixing show and create dims just makes things more
confusing.

IMO, this is the strongest part of your argument.


-TeamNike

We change the color of created dimensions so we can tell them apart. I have asked PTC to add the ability to configure dimension colors based on type so this would be automatic. Yes I have resorted to creating a dimension from time to time.

 

[dr_gallup]

BigJoe's friend here. Thought I'd chime in with my rebuttal to
dr_gallup as most of the users here seem to be newbies torn between 2
ways of modeling.

Boy does this guy have anger management issues!

Thanks for the psycho-analysis. I hope I can make it thru this rebuttal before I put my foot thru my monitor.

I've designed fuel injection systems that are running all around
the world in BMWs, Jags, SAABs, Vettes, etc. Safety & emmissions
critical components, not pastel cell phones.

I might've designed that pastel cell phone you own, but I've also
worked for some very prominent medical device companies...one of which
sells their product (blood glucose meter) to both hospitals and
consumers. I know what it is to deal with safety and the
FDA. But thanks for insinuating otherwise to try and boost your
argument.

Just getting some digs in without resorting to sounding like an episode of HBO's Deadwood. As Bugs Bunny would say, Unlax!

 

[Brian_Adkins]

>>I have asked PTC to add the ability to configure dimension colors based on type so this would be automatic


That would be nice. You can always go into Edit/Highlight By Attributes, but that's only temporary:


"Owned by a model" = shown
"Created and associative" = created
"Created but non-associative" = ??? (got me!)
"Not-to-scale" = @O dims
Edited by: Brian_Adkins

 

[BigJoe]

Hey Mizuno, how's that monitor?

 

[cristelino]

Big JOE


i never see that interest abbout a post (like you generate)

i tell you a joke:


BUDHA said:all is pain


JESSUSsaid :all is love


EINSTEIN said:all is soooooooo...................relative


i m sure you known allready

where is XCAD,Spelling,ADMINIDTRATOR,DougR???????????????

Cristelino

 

[donha]

There is one item which has been overlooked in this thread. If you use the "Show Dimensions", creating views as necessary, one feature at a time, you will have captured all dimensions necessary to create the part on the drawing. Using the "Created Dimensions" approach, you hope you haveincluded all dimensions necessary to create the drawing. How many times do we create an Engineering Notice due to a dimension(s) missing from a print?

 

[cristelino]

Show erase is not covering all drawing design necesary instances....... that s clear





Cristelino

 

[AHA-D]

Donha,


Even with model dimensions there are cases that you don't get the necessary information. Take for instance mirrored and patterned features, or features referencing from edges that are consumed during further modeling.


Since we're in CADCAM I prefer transferring the model for fabrication, or even the drawing. Since the drawing is accurately depicting the object I will allow people to take measures on the drawing or the model.


I've had aluminium profiles screwed up because people misinterpreted what they (think they) saw on the drawing, that would have been correct if they had just copied over the geometry.


On the other hand I wouldn't do this when I knew the drawing originated from Autocad ...


Alex

 

[magnusod]

dr_gallup


I'm rarely using any driven dims in my drawings but I must say that I'm very curious of how much you can use in advanced modeling parts.


I would be very grateful if you could post a part and a drawing here showing your technique of how to model a part and using the dims in the drawing. Of course it has to be an advanced part.


Just to clarify, since there are a lot of tension in this thread, I'm not doubting your way of modeling but want to improve mine.


Magnus

 

[brano]

EINSTEIN said:all is soooooooo...................relative


i m sure you known allready

Mileva (Einstein's wife): Absolutely!


And that is how this topic started, one dark and stormy night.


Keep going, we all learn something new.


Brano

 

[4KAD]

As an instructor, we teach ANSI Y-14.5-2009 as a rule for drawings, in which is stated in Section 1.4, category e: "The drawing should define a part without spedifying manufacuring methods. Thus, only the diameter of a hole is given without indicating whether it is to be drilled, reamed, punched, or made by any other operation. However, in those instances where manufacturing, processing, quality assurance, or environmental information is essential to the definition of engineering requirements, it shall be spedified on the drawing or in a document referenced on the drawing."


With regards to retreiving dimensions, if one is dimensioning the part himself, he will determine how they are placed with regard to design intent. If handing the part off for someone else to create the drawing, it is easiest for the drafter to retrieve the information from the model instead of guessing or the orginator creating a sketch with dimension locations. Kind of double-duty.


When in the midst of top-down design, it is hard to model with design intent. To redefine the model afterwards takes more time and is the best thing to do, IMHO, but schedule does not always allow such luxury.


Great post, guys! Nice to hear of this...another teacher sent it to me and found it interesting