V0.19 Top Down Assembly Design Using Assembly4--Update #11

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chrisb
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Re: V0.19 Top Down Assembly Design Using Assembly4--Update #8

Postby chrisb » Mon Sep 14, 2020 5:25 pm

By a mere coincidence I have recently seen this video: https://www.youtube.com/watch?v=JmSXo0XdWoA.
You need at least FreeCAD 0.19.23300 to edit my current sketches.
A Sketcher Lecture with in-depth information is available in English, auf Deutsch, en français, en español.
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mfasano
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Re: V0.19 Top Down Assembly Design Using Assembly4--Update #8

Postby mfasano » Tue Sep 15, 2020 2:42 pm

You have been doing great work for a long time. I have said I am always impressed when I visit the User Showcase, and your work does that. Your work with assembly 4 makes me confident about using it as a base for a multibody dynamics Workbench using MBDyn. MBDyn WB(shameless plug for my workbench)
HK sxx
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Re: V0.19 Top Down Assembly Design Using Assembly4--Update #2 Arbor Press

Postby HK sxx » Wed Sep 16, 2020 3:06 pm

Hello,
Some great work, thanks for sharing !!!

I am trying to model an assembly using the workflow described here. I am not able to start correctly, I think I miss something basic.

I can't do this:
This image is of a carbon copy of the master sketch which actually resides in the Model (assembly) portion of the tree ... A carbon copy of this sketch is then used in the first body in the Part folder.
The inset image is the master for all of the rotating bodies. Details are added to a carbon copy of this sketch to create each body which then becomes another carbon copy 'master' for all of its features.
In my first body, it doesn't allow me to make a carbon copy of the master scketch that is in the model assembly. In fact, it does not allow to make carbon copy of any sketch that is not inside the body itself.

I have tried to do it outside, with the sketcher workbendh, and then drag and drop into the body, but when I drag and drop it, the rest of the model objects out of the model.

Any advice would be welcome.

OS: Windows 10 (10.0)
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.19.22411 (Git)
Build type: Release
Branch: master
Hash: d4519d5aec15bc08f029da5ed15410a494b57b2c
Python version: 3.6.8
Qt version: 5.12.1
Coin version: 4.0.0a
OCC version: 7.3.0
Locale: Spanish/Spain (es_ES)
GeneFC
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Re: V0.19 Top Down Assembly Design Using Assembly4--Update #8

Postby GeneFC » Wed Sep 16, 2020 3:38 pm

This is explained in the wiki for Carbon Copy.

Code: Select all

If the sketch to be copied is not in the active Body, the mouse pointer will not allow selection. In this case, hold Ctrl to allow selection of sketches from other Bodies.
Gene
HK sxx
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Re: V0.19 Top Down Assembly Design Using Assembly4--Update #8

Postby HK sxx » Wed Sep 16, 2020 3:58 pm

GeneFC wrote:
Wed Sep 16, 2020 3:38 pm
This is explained in the wiki for Carbon Copy.

Code: Select all

If the sketch to be copied is not in the active Body, the mouse pointer will not allow selection. In this case, hold Ctrl to allow selection of sketches from other Bodies.
Gene
As expected, something basic :oops:

Thank you very much.
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bambuko
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Re: V0.19 Top Down Assembly Design Using Assembly4

Postby bambuko » Sun Sep 27, 2020 1:34 pm

ppemawm wrote:
Wed Jul 08, 2020 7:21 pm
...2. Changing the master sketch half way through the process. If you try to add or subtract geometry to the master it will most likely break any body or local coordinate system (LCS) that is dependent on the sketch. Modifying the sketch geometry will likely change the numbering of the edges and vertices. You can of course change dimensional constraints within reason...
Hi ppemawm
I am slowly going through this thread in preparation for my first assembly in FreeCAD and the particular comment (quoted above) is worrying me.
It is one thing "modelling" existing design and another thing "designing" something.
It is almost inevitable when designing, that half way through the process one needs to go back (whether few steps or right to the beginning) to modify, add or remove something that was not clear at the beginning of the process.

Of course when modelling an existing design it is relatively easy to plan your CAD work to avoid this, but designing is something else, at least in my experience.

Are you really saying that "...adding or subtracting geometry to the master sketch..." I will end up deep in shite?
What alternative strategy would you use for the type of project I have in mind, please?
Here is an example of what I am hoping to achieve in FreeCAD:

Image
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ppemawm
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Re: V0.19 Top Down Assembly Design Using Assembly4--Update #8

Postby ppemawm » Sun Sep 27, 2020 4:08 pm

bambuko wrote:
Sun Sep 27, 2020 1:34 pm
What alternative strategy would you use for the type of project I have in mind, please?
I suppose it is simply a matter of experience with master sketches. My mantra is "keep it simple but not too simple". Master sketches are all about top-down design intent and control. They definitely require you to thoroughly think through the design beforehand which is entirely useful in itself. Some are planners and some are not. Some like to learn to swim and others, jump in and flounder.

You can be sure that there were a myriad of changes in the models created in this thread but none that required a significant geometry change to the master sketches. Remember that you can always add to or subtract from the carbon copy for a particular body's features. So, not everything needs to be in the master(s). EDIT: See this example for an assembly design that did not use a master sketch for the assembly:
https://forum.freecadweb.org/viewtopic. ... 30#p430431

I would suggest that you start with the simplest of master sketches, e.g. interface dimensions only, and add detail to the master as you gain experience. I sometimes use a simple master for the top assembly, a carbon copy of it with added detail for the subassembly interfaces, and then a carbon copy of that for the body features' master. I would not nest them any deeper than that.

If you do not have much experience with the master sketch process I would not recommend you start with such a complex assembly unless you break it down into multiple sub-assemblies to simplify each master. Or, do not use a master. I always have since I discovered them, but you will probably find that most do not. If you Google mastersketch you will probably find much more info from SW, F360, etc..

Assembly4 does not require master sketches. So, I often use a mix of approaches. You can attach the assembly LCS's to the sketches used to create the interface features in each body. For example, to create a bolt hole feature you probably have a sketch with a circle. Attach the hole LCS to that circle then you can attach the bolt LCS to that LCS during assembly and you will risk a minimum amount of damage due to changes. Just do not attach LCS's ( or sketches, datums, etc. for that matter) to feature faces, edges or vertices or you will be more vulnerable to the topological renaming demon which is FreeCAD's Achilles heel.

It definitely takes some experience with FreeCAD to avoid the topological renaming problem, but once you understand the culprit it gets to be second nature. Who in the world would want to attach to faces anyway...? :roll:

Realthunder is coming to the rescue.
"It is a poor workman who blames his tools..." ;)
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bambuko
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Re: V0.19 Top Down Assembly Design Using Assembly4--Update #8

Postby bambuko » Sun Sep 27, 2020 5:36 pm

Thank you ppemawm for your detailed comments and advice.

The more I read your threads, the clearer it is to me that whilst FreeCAD has plenty of mysteries to me, the process of designing is the same and an old familiar one, just that I never used the term "master" sketch (I guess there were some gaps in my education and training :P )
It is clear that not everything needs to be in the top(master) sketch.
As for geometry changes, yes they can cause problems in any CAD system, just that some of them are more robust and user friendly when it comes to recovering user created mess :D
I suppose only time and practice will tell me whether FreeCAD is what I am hoping for...

I will have to do more reading about how you use LCS for almost anything :P and the business of "attaching LCS sketches and datums" to anything but faces, edges etc.

Now is the time to stop overthinking it and start using FreeCAD :mrgreen:

Thank you again!
arnn
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Re: V0.19 Top Down Assembly Design Using Assembly4

Postby arnn » Wed Sep 30, 2020 1:53 pm

Thats a great tip.
aapo wrote:
Wed Jul 15, 2020 7:17 pm
I would like to add one tidbit of information concerning this master sketch LCS jumping phenomenon. I have found out that it is a great help to use map mode OZX, i.e., the "Align-O-Z-X" (or any of the other coordinate permutations) attachment option. There, you first select an Vertex from the sketch, which will become the LCS origo. Second, you'll need to select an edge starting from this same origo, which will become your LCS z-axis. Finally, one must select the x-axis. I usually choose a datum axis, which I have put perpendicular to the sketch plane. This way your z-axis cannot point the wrong way, unless the points in your sketch are rearranged (topo problem), which happens very rarely at least for me. It is still possible for your x-axis to point exactly into the opposite direction you have planned, but even that happens very rarely. One of the downsides, at least for me, is that FreeCAD complains when I've mapped the first Vertex and Edge, but if I just won't care about the warning and stubbornly add the 2nd Edge, OZX suddenly becomes possible. :D


20200715_FreeCAD_Asm4_Align-O-Z-X.png
jemcomcast
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Re: V0.19 Top Down Assembly Design Using Assembly4--Update #8

Postby jemcomcast » Thu Oct 08, 2020 2:35 pm

I am trying to design an diesel engine model from plans in a Magazine, however those plans have many errors, and I want to convert to inch. So I was using FreeCAd so I could analyze the model for problems. I just recently found this post, which I realize I have should switch things to using a master sketch, especially to animate the movement to check for problems. You mention that you would be willing to provide some of your examples via PM, however, I guess since I am a new member (although I have been reading the forum for many years) I cannot use PM? I know you cannot share the aero motor model, but I would be interested in the Arbor press (or other examples that animated the gears, plus uses two master sketches), and the Blowtorch. I am interested in where you placed the two master sketches that you mentioned?