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  #1  
Old 09-28-2010, 07:38 PM
cadcoke5 cadcoke5 is offline
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How to keep cylinders cocentric?

I am a new user, and am having problems modifying a model.

I have a flanged bushing (see attached pictures) I created by revolving a simple 2d sketch. Then I attached 3d dimensions. Now I want to edit the thickness of the bushing wall. But, when I do I end up repositioning the cylinders that form the bushing, so that they are no longer concentric.

In an attempt to force the cylinder to stay centered, I added dimensions between them, which show as 0". But, that doesn't work.

Any more ideas?

Joe Dunfee
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  #2  
Old 09-29-2010, 12:51 AM
Marten Marten is offline
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Re: How to keep cylinders cocentric?

Using dimensions for these tasks is making it more complex than needed. Just select the cylinder you want to modify, and use the 'change radius' command. If you want to use dimensions I think your best option is this:

1. Click the cylindrical face
2. You are in the Change Radius command automatically. Click on the 3D Copilot arrow.
3. You can now drag the face to the new value, but you want to specify the thickness. To do this click on the blue sphere.
4. A red arrow appears. You can drag this arrow to the inner cylinder
5. You can now set the dimension of the thickness. The outside cylinder will change to the right dimension.

The way you want to do this indicates you are trying to do it the 'history based way' and probably don't know CoCreate Modeling uses another concept of creating and modifying models. So I want to give you some extra information:
CoCreate Modeling is a history free cad application. The new 'Create Anno' function is not intended to make the model completely constrained in order to make it dimension driven (like with history based modelers). It is just there to make some modifications easier. If you want to learn CoCreate Modeling it's best to let go of the modeling concepts you already know from working with history based applications and to try working with CoCreate in the way it is designed to be used.

With CoCreate modeling you create the model the way you want it to become, not how you want it to be created. So, when you want to modify the model you just modify the geometry and not the values of your model 'blueprint'.
It's more like claying: you add material or remove material to modify your model. With history based modelers you are a programmer: you program how the model should be constructed. When you need to modify it there are two options: change the program, or change values in the program.

Those two concepts are fundamentally different. If you want to work with CoCreate in the 'programming' way you are going to be disappointed, because CoCreate isn't meant to work like this. If you try to embrace the 'other way'. I think you will start to value the ease of use: you don't have to think about what's the best way to construct your model in order to make modifications easier. You just create the model. However, it will take time to become used to another way of thinking.

Good luck!

Regards,

Marten
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  #3  
Old 09-29-2010, 01:21 AM
cadcoke5 cadcoke5 is offline
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Re: How to keep cylinders cocentric?

Wow, thank you for such a detailed reply. I had been aware of the "history free" concept, but it definitely takes some getting used to. In my work, rarely do I draw something without either knowing its dimension, or need its dimension to be determined by something else.

On this particular model, I would also like to be able to change the inside diameter, but not change the wall thickness. In other words, if I now want to use this bushing on a 3/4" Diameter shaft instead of the 1" I have it currently modeled at, I would like the 1/16" wall to stay at 1/16". Currently if I change the inside diameter, the thickness changes. I would like to lock the 1/16" dimension. Is this possible?

I am also wondering if there is a way to make an assembly parametrically adaptive. For example, if this bushing is used in an assembly, can I make it so that the bushing will adapt to the size of the shaft?

I realize that both of the above paragraphs are standard things for programs like Pro-Engineer, but can CoCreate do them?

Joe Dunfee
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  #4  
Old 09-29-2010, 01:42 AM
Marten Marten is offline
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Re: How to keep cylinders cocentric?

Hi Joe,

Yes, you can do this. You need the parametrics module for this (part of advanced design), and when you modify the model you need to specify that CoCreate Modeling updates the parametric relations (as relations are never enforced, they are always optional).

However, CoCreate users don't work this way (they only use it in special cases). As with the dimensions, it is not the CoCreate way. When you add the parameters, you add complexity to the model which could lead to unintended changes. This is because you need to specify up front what changes are allowed. when you need to change the model later on you probably don't remember which relations are added (especially when you use the model created by someone else). When you modify the model while you don't exactly know all constraints you have the risk of changing something you didn't want to get changed, as your change isn't always the same as the intended change when creating the constraints.

With CoCreate modeling you change what you need to change. Adding the relations you mention doesn't help. When you are going to change the inside diameter, you definitely know (at that point) that you need to change the other diameter as well. In CoCreate you don't need to edit separate parts, so what use would those constraints have? It could probably save you one click because you don't need to select multiple faces, but you need tens of clicks to add the relation, so what's the point of this? With CoCreate you just select the cylindrical faces you need to change and change them (one command). All changes are directly on the faces you select, so you won't get any unexpected side effects. What you see is what you get!

One tip: use the command 'Radial offset' to change the multiple cylindrical faces in your situation.

Regards,

Marten
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  #5  
Old 09-29-2010, 01:45 AM
Marten Marten is offline
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Re: How to keep cylinders cocentric?

Oh, forgot:

This thread is also about a user which tries to use CoCreate the SolidWorks way:
http://www.cocreateusers.org/forum/showthread.php?p=23796#post23796

Mike added a link to some online webinars; maybe they are useful to you as well:
http//www.ptc.com/appserver/wcms/standards/textoimgothumb.jsp?&im_dbkey=115967&icg_dbkey=841

Regards,

Marten
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  #6  
Old 09-29-2010, 05:38 AM
cadcoke5 cadcoke5 is offline
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Re: How to keep cylinders cocentric?

Thank you all for the detailed replies. I am a long-time SolidWorks user, and have also used Pro-E and Inventor. The pain of trying to figure out someone else's complex model is definitely real. I do like the idea of direct control... though there are times I wish I could to a few simple thing. But, at the moment I am unemployed, so am not in a position to buy any software.

The "bushing" design I am working on is actually for a laser turret for a robot to use in navigation. I have been given the opportunity to print a sample object on a rapid prototyping machine, so decided to design this. My first version of it was modeled using BrisCAD, an AutoCAD clone. It is doing solid modeling the way AutoCAD did back in version 10 with the AME Extension.

Here is a picture of what I did in AutoCAD.

Joe Dunfee
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  #7  
Old 09-29-2010, 06:52 AM
Marten Marten is offline
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Re: How to keep cylinders cocentric?

Hi Joe,

Hope you find a job soon... In the mean time Modeling PE is a good way to learn another way of 3D modeling. This way you can get a wider view of your options. I know you will come across some situations where you would like to have the history based approach. Sometimes you can find a reasonable way to perform the modification in CoCreate, but sometimes it's just harder. This can be because required functionality isn't available (yet) in CoCreate, but it also because of explicit modeling. Parametric in such situations is the way to go.
As with everything, CoCreate also has advantages and disadvantages. No tool is perfect. I do believe however that for 'engineering to order' and prototyping (one-off designs, maybe even copy/paste from other designs) explicit modeling is definitely the way to go. In specific situations history based could save you some time, but in total it is a restriction on your freedom to design and modify. And even if some modifications take a little bit more time (though I think this is a very small part), at least you can make a good estimate about how much time it will take. With history based systems it's sometimes hard to estimate the time required to make a modification: it can be a few minutes or it can be several days. Especially when you didn't create the model yourself.

Good luck with exploring explicit modeling...

Regards,

Marten
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  #8  
Old 09-30-2010, 10:00 AM
mrstero mrstero is offline
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Re: How to keep cylinders cocentric?

it is unfortunate that cocreate has had such a low market share for so long. perhaps if it had been marketed better it would be more widely used...hopefully Lightning will propel explicit modeling to the masses...
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