#16
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Re: OneSpace vs. SolidWorks
Marten:
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Yes, this takes careful thought with the creation of each feature - as it should if you are a careful engineer. Not a single face exists on a part without a purpose, or you would not have put it on there. Why not capture what that purpose was? Quote:
If your design intent is to have 5 holes evenly divided along the length of the part, you parametrically establish that sort of pattern so that no matter how the part length changes, you will always have 5 holes evenly divded in that linear direction. If your design intent is that the holes need to be centered to the model, then you establish that relationship. If your design intent is that the holes need to be on the same distance to one side, then you establish that relationship. If you don't know how many holes are needed if the part grows in length, then you have an engineering problem, not a CAD problem. Once you have determined the engineering requirement, then you can set up your model so that when the part is, say, less than 1000mm long you have 5 holes, and if it is over 1000mm you get 6. Or you can even set up a relationship to drive the hole array to achieve a certain "negative area" - the amount of open area the holes are required to provide based on the number of holes present and their size. If you can't answer these questions at any particular time in the design - NO PROBLEM - you don't HAVE TO. Many parametric, history-based software packages such as Solid Edge, Solid Works, and others don't require the constraining of sketch geometry in any way. The point here is not that you have to create design relationships in your geometry, the point is that you can. I tend to lock things down just as soon as I am able. Why? Because I can forget about them from then on and they will take care of themselves. Quote:
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And the heck of it is, this is a trivial example of the problem. Try modeling up injection-molded or cast parts of any complexity at all and then have a need to go back and modify the underlying basic cavity sizes that have all been lost under drafts and blends and you will find yourself pulling your hair out. I know from experience. Quote:
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#17
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Re: OneSpace vs. SolidWorks
(continued)
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Yes, sometimes you have to do this in a history-based system, also, but at least you know which ones to delete. Quote:
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Steve |
#18
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Re: OneSpace vs. SolidWorks
John:
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Not only this, but the parametrics in OSD are pretty much an all-or-nothing proposition. Unlike feature-based modelers, where you can simply click on a feature and the relevant parameters will light up on-demand, with OSD they are always visible. Yes, there is a browser window you can use to turn off and on individual parameters but unless you have given meaningful descriptions to each parameter it is difficult to tell in the browser which parameters go with which feature(s) on the model. I found the parametrics so cumbersome to use that I, a parametric freak, gave up using them in OSD. Ron: Quote:
Steve |
#19
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Re: OneSpace vs. SolidWorks
Well, the post just keep getting longer:-) But hey, it keeps you busy.
You make it sound like dynamic modelers are designed stupidly, and are only for the engineering underclass. Well, I certainly don't agree with that. Both history based systems, and dynamic systems have their advantages/disadvantages (don't know why you call it boolean. It's definitely not just on/off). You just can't say one is a better technique, and the other is just for the stupid users. In some situations history based can be useful, and in others dynamic is. I do think dynamic systems are more productive and faster for most mechanical cad areas. If you look at One Space, it to has some history added where it makes sense. Blends for example are history features. When you modify the geometry, it will temporarily remove the history, and then re-apply it. Even your taper-example can be added while keeping the history. (I looked at it further, and found you can add a taper as a feature. Then, you can suppress the taper, modify the cylinder-diameter, and re-enable the taper). But all those history / features never become a burden. If you modify the geometry in a way which breaks the history, it will simply be removed. You don't get an error telling you this feature can't be created anymore. Quote:
Maybe you can show me how, but I have never seen this in a history based modeler. If you have a model without constraints, you cannot change it without constraining it. I have never seen it without having to manually remove the constraints/history (which you won't do, because it takes extra time). In my opinion, it is fair to say that, in history based modelers, you are required to have history. It is not an option, or a choice. About the design intent. With the history based approach, you don't just capture design intent. You capture how the model is created. With that, you sure can add design intent, but that is definitely not the only thing you add. History based is not the same thing as parametric! One Space has a parametric module, but in my opinion, it's just there to be able to say it's there. But when it has a nice implementation, I would still only use it in special cases. Quote:
Well, the current design intent is the model. If you want to document your design intent/choices, you should just document them (and only the relevant ones). If you enforce all your design choices, you make it important how the part will change in the future. If you change your model, it means that your design intent has changed. So your enforced design intent probably doesn't apply any more. As soon as you change your design, the engineer that changes the design is responsible for the new design. And remember, in a history-based system, you have to add the enforced constraints. So, when you don't care about how the part can be changed in the future (for example, because your part will be manufactured only once and you don't want or have the time to think about how your part should be changed in the future), you will end up with a model which will most likely have wrongly defined constraints. Because you have to create those constraints, you will end up with a model which behaves unexpectedly when changed, and is harder to change, because you have to find out how it is created. Adding “good” parametrics (as far as that's possible) takes a lot of time. Not everyone can invest that much time in a model. It's not: if your smart enough, you would add them. You should also take time into account. If time wasn't a problem, you would also always calculate the minimum material required to meet the strength requirements. However, not everybody has the time to do it. It's sometimes much faster and cheaper to just over-dimension. Another problem with your statements about design intent and engineering requirements is, that many cad users often only have functional requirements for the machine/product they are designing. So, because the end-product isn't completely clear yet, those engineering requirements are not defined completely. Many of the engineering choices change very often during such design process. During this design process, it would constantly take a lot of time to put all the possible constraints into place, and then, when you think: “Oh, I can do it better this way”, those constraints make it harder to change your design. Yes, it would be nice to be able to add some of your design choices into your model as constraints, but only when it can be done after you completed your design or part of your design, and when it's easy to remove all of them (and still be able to modify your model). Quote:
Again, this discussion about adding design intent has nothing to do with being a history based or a dynamic modeler. It is just about being able to add parametrics to your model. History based systems by definition allow (and even require) you to add parametrics, but that doesn't mean that you have to be history based to be able to add them to. CoCreate could add good parametric abilities in Designer, but you have to see this as an extra feature which can be added to the software. It's not that high on my list of enhancement requests btw. One thing that's absolutely clear to me, is that it should be optional to add those parameters. Then there is the discussion about history based vs dynamic. I think history based approach can have some advantages. In some cases it allows you to easily change your model where, with dynamic modeling, it's easier to just rebuild (part of) the model. I believe you are in the business creating plastics moulds or something? I can imagine that history based can have advantages, because you constantly work with those tapered faces. I think that when you work with not that many parts, and have complex parts (to create), and where the design is pretty stable (ie. won't change that much), it can be useful to have a history. However, if you are working with many parts or change your design frequently, or where most parts are fairly simple (and thus easy to manufacture; where the complexity is in the combination of these simple parts) I think dynamic modeling has many advantages. The few cases where history would help to easily modify? Well, to bad. Not that big of a deal. I think this is true for a very big part of the industry which manufactures machines. Tapered cylinder One last remark about the tapered cylinder: Yes, you can measure the distance. Because measuring the distance from the conical face to the circle will give you the normal offset required. The normal is the shortest distance to the circle, and that's exactly what's measured when measuring the distance between the conical face and the circle. Also, if you un-taper, modify and re-taper, you will not mess with dimensions in annotation when you just modify the face. You will only get problems in annotation when you remove the face (for example with mill) and then recreate the taper. But hey, CoCreate did listen to you and created a taper-feature. It would be nice if they also created a “suppress taper” command in the right-mouse menu in the structure browser, but that will be easy to create in lisp if they don't. I'm curious what you think about this little bit of history in OSD With kind regards, Marten Verhoeven |
#20
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Re: OneSpace vs. SolidWorks
This is such a fun topic; I can’t resist making this post even longer. J
There are many terms flying around here that I think are being abused. How about a little history (no pun intended) lesson on 3D modeling? It all started ….. now I am going to show my age ( And I know there are others out there that are as old as me that can correct my mistakes here.) Back when 3D CAD first came into existence, there were several basic technologies that were used.
CSG, in it purest form is no longer used in mechanical CAD. The last systems to use this technology was I-deas from SDRC and Catia. The issue with pure CSG was the low accuracy of the primitives and the limited set of primitives. Models were constructed by applying these primitives to the model with 1 of 3 Boolean operators: union, intersection and difference. There is one very important component of CSG, however, that is still in use today and that is the “structure” or “tree” of primitives and Boolean operations. The basis of today’s “history trees”. B-Rep is by far the most accurate technology for representing 3D geometry, and is used in all modern CAD systems today. It was first used commercially in a geometry kernel called Romulus. The Romulus geometry kernel was used in several 3D modeling systems in the 70’s and 80’s: Anvil, Graphtec, ME30, Unigraphics and a few others. Many of the people that helped develop Romulus came together again to develop ACIS. This geometry kernel is in wide-spread use in many of today’s modern 3D systems. Romulus was also the forerunner to Parasolid. Another geometry kernel that is in wide-spread use today. In the early days, B-Rep modeling gave us accuracy, but developing and modify models was very difficult. Many time we resorted to creating primitives and performing Booleans on the model just to make a simple change. This was termed “explicit modeling”, and was somewhat painful and time consuming. So where does “history” and “non-history” fit into all of this? Well both are based on technologies above. History-based modeling.
Well, you just have to decide what is best for you. I am familiar with one company that is a leader in innovation in their industry and they don’t use CAD, except to finally document what the designers design. It’s fascinating and reminds me of the good old days. I personally think we waist way too much time messing with our CAD systems rather than designing and inventing stuff. This seems to be especially true with history-based modeling users. It’s like a kid with a Rubik’s Cube. For pity sakes, peal the stickers off and move on. |
#21
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Re: OneSpace vs. SolidWorks
Very nice informative post Paul.
It reminded me of when we first started using CATIA at IBM. The beginner training we received did not include any details on the underlying CSG tree and how to properly manage it. The result was what we started calling the "CSG vine". If you looked at the CSG tree for most of the models that new users created, it was basically one long branch of sequential one at a time operations. This made future modifications difficult. As I learned more about CATIA and how you should use it to create a proper CSG tree, I remember thinking that it was unfortunate that designers had to think about what CATIA was doing under the covers in order to use it effectively. When I moved to HP and started learning an early version of SolidDesigner, it was a pleasant surprise to discover that I no longer had to worry about the CSG tree.
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John Scheffel |
#22
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Re: OneSpace vs. SolidWorks
Thanks John.
I received a few questions about which modelers fit where. I think this is close, unless things have changed recently: Hybrid Modelers: ProEngineer, SolidWorks, Solidedge, NX, UGS, Caita, IronCAD, Inventor, Alibre, … and a lot of others B-Rep Modelers: OneSpace Modeling, SpaceClaim, Kubotek |
#23
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Re: OneSpace vs. SolidWorks
Thank you Ron Keeley for quoting my blog (about SpaceClaim).
In order to understand better how SpaceClaim is different from traditional parametric-feature-based system I invited Howie Markson of SpaceClaim for an interview. I asked very specific questions trying to get as much info as i could from him. I think the interview can help to better understand this new product and the company strategy. Anyway, if you are interested, the complete interview is available on (my) Novedge blog. Franco Folini |
#24
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Re: OneSpace vs. SolidWorks
When reading their blog, just keep in mind that Novedge is a software reseller/distributor who does not sell CoCreate products, but products for several other competitive CAD markets - at least as far as I can tell (correct me if I'm wrong).
Claus
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CoCreate Modeling FAQ: http://www.clausbrod.de/CoCreateModeling/ |
#25
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Re: OneSpace vs. SolidWorks
Claus,
thank you for your note, you are right about Novedge. I would like to add that we do NOT sell SpaceClaim, SolidWorks and CoCreate. IMHO this put us in a "almost" neutral position when talking (or writing) about those CAD systems. Franco Last edited by folini; 06-11-2007 at 08:50 AM. Reason: fix |
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