Best ways of modeling surface area details?

traveler_hauptman

In mechanical design there are a bunch of important details that need to be captured in the design and then communicated to fabricators can't easily be modeled with geometry. Most often they are a specific part of a surface.

Examples include:

• Varying surface finish or tolerances on different parts of a surface with a constant nominal dimension (a shaft for instance)
• Masking, painting, adhesive, and other applications to specific portions of a surface.
• Threads, knurls, roughing grooves, on surfaces where adding the actual geometry takes too much time or compute resources.
• Aesthetic tool mark patterns.

What are your favorite methods for capturing and displaying this info in other CAD systems? What would you like to see in Onshape?

shashank_aarya

I would like to add GD and T also in the list. In Creo there is one best practice to use GD and T. In that user can define datum references and GD and T in part, they can be shown later in drawings.Similarly when GD and T is applied in drawings, it can be seen in parts also. So there is no conflict between part and drawing. So, I hope that it could be a suggestion which we can suggest when drawings will come.

andrew_troup

This class of problem is just one of a number of difficulties with the fashionable but (I think) impracticable notion that 2D drawings are passé
Until such time as these (and many other) extrinsic designations of part characteristics are standardised, not just across CAD packages but across the international engineering community, it's not going to be feasible to base contractual commitments on 3D models.

pete_yodis

@andrew_troup I would respectfully disagree to some extent.  The economics will ultimately drive the need for 3D models only.  It's so much more efficient in the long haul.  I think in the past there was so much of a desire to use 2D drawings, that models weren't treated as they should be.  I think we are seeing this changing.  Additional efficiencies are being wrung out of the design and manufacturing process and the silly notion of a model AND a drawing being always needed (notice...not ever needed) is certainly within the sight of a lot of people.  The problems that are brought up are all solvable problems and I think the passe that you refer to is actually the market saying to the CAD companies... COME UP WITH A SOLUTION!

pete_yodis

I think what @traveler_hauptman is after is: how can we do this currently in Onshape and or how could we do these if we had some tools to get it done?  Is that right @traveler_hauptman ?

traveler_hauptman

@pete_yodis Onshape does not yet have any way to capture information about surfaces in the model. I hope they add this capability eventually. I was hoping for info on how people do this in other CAD packages or what they would like to see in Onshape.

I'm really thinking about information capture. How do I keep track of the fact that part of a surface needs to be treated differently. How can someone else opening up the design understand that.

Regarding 2D vs 3D, I think it's a silly argument. One uses the form of communication that is most effective and efficient for the situation.

andrew_troup

traveler_hauptman said:

Regarding 2D vs 3D, I think it's a silly argument. One uses the form of communication that is most effective and efficient for the situation.

Indeed, it is silly, chiefly (I think) for the reasons you give. It is also asymmetrical: it's actually not a question of 2D vs 3D, because NOBODY is arguing against the use of 3D. People from that "side" of the argument would not be posting on this forum if they were against 3D representations where they make sense.

However there is a subset of the opposite side of the argument who wish to deny all users the option of 2D representations, presumably on the basis that if they cannot access them, they will be forced to find some way to force 3D representations to act as an acceptable substitute. 
Which, for some requirements, would be not just silly but impracticable. 

The bar 3D has to meet, before it can "go solo", is set remarkably high: communicating unambiguously, as well as effectively and efficiently, and into the indefinite future, in all aspects of all fields of endeavour, in all locations and operating environments of the world where stuff is built, appraised, inspected, maintained, and litigated about.

Exploring just one of these points: items with long lifetimes are a particular case in point. Who can still read 3D models produced by mainframe systems, like Prime, or even the workstations which followed them, like Ideas? The most obvious situation where this matters, but by no means the only one, or even the most important one: Large expensive engineering installations (say, an ultra-high tonnage press or ultra-heavy lift crane) have long payback and very long service lives, sometimes a great many decades.

Moreover, certain inherently dangerous technologies (not just the obvious nuclear plants, but things like highly pre-stressed concrete structures on a sufficiently grand scale) can be tricky to decommission safely, and this might have to happen a long time into the future.

The most durable means of accurate communication ever devised were pottery tablets, stamped with wedge shapes and then fired. They are still, in many cases, virtually unaffected by the passage of many thousands of years since they were 'written', and it's paradoxical that the most fleeting communication technologies, in general terms, are the most recent ones.


And it seems to me that to suggest CAD companies can drive the eradication of 2D is a bit like suggesting a technology provider bloc, such as machine tool builders, could have driven the US to abandon inch/pound measurement in the 1950s.

traveler_hauptman

@andrew_troup While I agree with you, I think this discussion has been hashed out enough elsewhere on the forum.

Perhaps I phrased my original post poorly. I'm asking about good ways to capture the information for the designers so that design information is centralized. I'm not implying that the subsequent communication to fabricators should be 2D or 3D. 

Currently in SW I capture surface treatment info in drawings, which means that someone opening up the part does not have all the information they need at hand.

I currently create a super thin extrude or revolve at the location of the surface treatment so that the boundary line is visible on the drawing. This is a bit of a hack.

There are locations on some parts that need a logo, or laser mark. Onshape currently has no way to apply a bitmap onto a surface.

These are the kinds of things I'm talking about.

andrew_troup

Apologies for unwittingly derailing your topic. I will desist.

traveler_hauptman

No worries. It's all good. I'd rather have productive argument than polite misunderstanding.

pete_yodis

traveler_hauptman said:

@pete_yodis Onshape does not yet have any way to capture information about surfaces in the model. I hope they add this capability eventually. I was hoping for info on how people do this in other CAD packages or what they would like to see in Onshape.

I'm really thinking about information capture. How do I keep track of the fact that part of a surface needs to be treated differently. How can someone else opening up the design understand that.

Regarding 2D vs 3D, I think it's a silly argument. One uses the form of communication that is most effective and efficient for the situation.

@traveler_hauptman I am curious to hear about what others bring from their experience in other CAD packages.  I am also a SolidWorks user and haven't seen a lot of great things to help in this area, but I suspect there are things that haven't yet been answered well enough in the industry in general and I think this goes back to not considering the model at least on par with the drawing.  With SolidWorks and others that I have seen there is an ability to attach annotations to surfaces as well as bitmap textures.  I think this is helpful, but not machine readable.  My thoughts... we need a way to codify surfaces.  Surfaces of models need to be treated like you treat classes in OOP.  They could have objects and properties to help define what's happening.  If that could be done, then we could make this information universal and machine readable.  For any type of information we could think of, we could make a class for that type information.  Our 3D model could then get pushed through standardized compilers (I think this is really what STEP is like...) that could then be translated to information pushed to inspection machines, CAM packages, drawing packages (yes, we could pluck the surface info right off the model definition and show it in the drawing), etc...  On the flip side if CAD packages read a standardized definition it could apply things like visual textures to surfaces to let users visually know something is different.  I think there is something here... let's keep the good stuff rolling.  Anyone else?

Please hear what I am trying to convey with regards to 2D drawings so that we don't have any polite misunderstandings but rather some more good and productive thinking together...  Don't let the shortcomings of a modeling tool drive us to ALWAYS need a 2D drawing to entirely convey what's needed.  I think your post is right in line with this thinking.  If we can think about a better modeling tool, then the user has better choices in front of them on whether just the model works in the current circumstance or whether a 2D drawing is also needed.  Current packages have not given us enough choice and for that reason we are still using 2D drawings, when they might not really be needed in a lot of scenarios.  Onshape has such wonderful potential to lead the way here in this realm for a lot reasons, one if which the viewer is inherent with the data.  I would hate (and I think most everyone here) to see it nail it on the platform and come so close to getting it... but not quite there on the robustness of the model definition.

billy2

Traveler



In SW, I use splits a lot to do what you're describing. I guess this maps to a trimmed surface definition which is basic geometry which all CAD systems should support. Hoping OS supports these operations soon.

Love the meta data attachment OOP scheme that you're talking about. I guess we could define the toString() method to call out the meta data associated with underlying geometry object.

The big picture, I don't think a standards committee getting their act together and pulling something like this off. I do see a small start up CAD company defining this system and industry using it. Much like DXF and the whole autodesk thing. Let's just hope it's a better standard than DXF.

pete_yodis

@billy Yes, standards organizations might be too slow, political archaic, etc... I don't know about the atmosphere there.  There is no reason we Onshapers can't start a little somethin'.  That's how things get done.  We see the potential and then start to push for it.  The standards organizations could play catch up.  That is how it seems to happen anyway right?  We shouldn't look to them to tell us how to do it.  We should tell them this is what we have figured out.  You (standards orgs) make it have teeth once and if it gains traction.  How about it?  Let's throw the hammer down.

billy2

Let's not throw any hammers. Someone could get hurt.

If I wrote the code, would you try it?

pete_yodis

billy said:

Let's not throw any hammers. Someone could get hurt.

If I wrote the code, would you try it?

@billy Absolutely.  If your code is any good, I'll start

billy2

It might be around Christmas time when it's ready, all the pieces are formulating nicely now. I'll keep you posted.

pete_yodis

Sounds great. I'll help with what I can.