Assembly 4 workbench

[drmacro]

In Assembly 4 workbench.

- create a file
- Create a new Assembly 4 Model
- Create new Body
- create new sketch in Body
- draw sketch and pad
- select Model, click Add LCS
- select edge for attachment, say an arc, select coincident
- LCS is created

But, some times a warning is thrown Links go out of the allowed scope.
It appears to be only on the first LCS inserted.

But, subsequent use of the part in an assembly throws the error on all LCS's.

Am I creating the part file wrong?

[Zolko]

- Create new Body
- select Model, click Add LCS
- select edge for attachment, say an arc, select coincident

But, some times a warning is thrown Links go out of the allowed scope.
...
Am I creating the part file wrong?

This happens because the LCS and the attachment geometry are in different coordinate systems: the LCS is in the Model, the arc is in the Body. You can check what can go wrong by moving manually the Body inside the Model: the LCS will not follow.

So you can do 2 things: place the LCS in the Body, or, better, create the LCS in the Model first, and then create the geometry in the Body referenced to that LCS: it will ask you whether you want to create an independent copy, a dependent copy, or create a cross-reference. I always choose the cross-reference. You can also use a datum Point instead of an LCS, this way you can use that point directly in a sketch for example.

[drmacro]

This happens because the LCS and the attachment geometry are in different coordinate systems: the LCS is in the Model, the arc is in the Body. You can check what can go wrong by moving manually the Body inside the Model: the LCS will not follow.

So you can do 2 things: place the LCS in the Body, or, better, create the LCS in the Model first, and then create the geometry in the Body referenced to that LCS: it will ask you whether you want to create an independent copy, a dependent copy, or create a cross-reference. I always choose the cross-reference. You can also use a datum Point instead of an LCS, this way you can use that point directly in a sketch for example.

Ok, I understand why now.
Now trying to confirm I understand how to use the LCS and attachment in a larger assembly context.

The part I described before is thus:

A1.png (115.37 KiB) Viewed 2387 times

I added the LCS_#_frame, and LCS_1_pivot because I thought this was the correct way to "define" the attachments that would be used later in the assembly to locate the object to other parts and to locate things to it (for example a bolt in one of the holes.

Do I have the concept wrong? Or have just missed the correct way to build a piece of the assembly?

[Zolko]

Do I have the concept wrong? Or have just missed the correct way to build a piece of the assembly?

This is correct, but since Asm4 v0.9 you can do it simpler: if you want to design a single part with the PD wb, you can use a Body directly, no need to wrap it into a Part or a Model. In a new file, create a Body, do your stuff, add LCS as you did, and you can insert (link) this Body into an assembly.

You still can use a Part, but it's really useful only if you have multiple solids, or to hold imported parts (from step for ex), or if you design with the Part wb.

Using a Model is either because you need the variables, or because you want to insert other parts (including fasteners).

Does that make sense ?

[drmacro]

Do I have the concept wrong? Or have just missed the correct way to build a piece of the assembly?

This is correct, but since Asm4 v0.9 you can do it simpler: if you want to design a single part with the PD wb, you can use a Body directly, no need to wrap it into a Part or a Model. In a new file, create a Body, do your stuff, add LCS as you did, and you can insert (link) this Body into an assembly.

You still can use a Part, but it's really useful only if you have multiple solids, or to hold imported parts (from step for ex), or if you design with the Part wb.

Using a Model is either because you need the variables, or because you want to insert other parts (including fasteners).

Does that make sense ?

- "do your stuff, add LCS" I assume this means add a PD WB LCS, (since when in file with PD Body and A4 WB selected LCS is grayed out?)
(the work flow between add LCS in A4 and PD is a bit different, i.e. PD LCS doesn't ask for a name first. No problem, just an observation.)

- I think I got the idea all parts had to have a wrapper from the tutorial where the STEP model is wrapped before use.

I think I grok it at this point...I'll be using A4 today, we'll see if I'm right.

[drmacro]

When I insert a fastener then attach it, other fasteners don't show in the list of possible attachment sources. (i.e. if I wanted to attach a nut to a washer.)

Is this correct?

FreeCAD Assembly 4 workbench
Current version 0.9.4, 2020-05-25

OS: Ubuntu 19.10 (XFCE/ubuntustudio)
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.19.
Build type: Release
Branch: unknown
Hash: 24bb210a0ce479b68f5f2fdcf4c7915e2949d7bb
Python version: 3.7.5
Qt version: 5.12.4
Coin version: 4.0.0a
OCC version: 7.3.0
Locale: English/United States (en_US)

[Zolko]

When I insert a fastener then attach it, other fasteners don't show in the list of possible attachment sources. (i.e. if I wanted to attach a nut to a washer.)

Is this correct?

yes. It's a choice, because if you have a lot of fasteners, the list can become very long. Dunno if it's a good choice though ...

[drmacro]

yes. It's a choice, because if you have a lot of fasteners, the list can become very long. Dunno if it's a good choice though ...

Hmm...not sure either.

I can see the list getting pretty long, real quick.

I guess if the desire is for a fastener "set" (i.e. bolt, washer, lock washer, nut) to stay with each other it could be a sub-assembly.

(Side question: Is it possible to toggle all LCS display on/off?)

[Zolko]

(Side question: Is it possible to toggle all LCS display on/off?)

no, I don't think so, and it's something that is really missing in FreeCAD. Same for selection filters. I would say that these UI enhancements should be the goal for v0.20

[learner]

(not working): Move the LCS from its default position (straight orange arrow) up to the top corner (curved green arrow)
...
When I try to do this with Right-click -> Edit datum, I can select features on the model, but nothing changes in the parameters dialog.

This is because the MapMode isn't App::Link aware, meaning that you cannot use the Attachment Editor of the Map Mode to attach an LCS to a geometrical feature in a linked part.

... if you want to use an LCS in a sub-assembly to attach that sub-assembly to a higher level assembly, and you want that LCS to correspond to some particular position in a child part of the sub-assembly, create an LCS in the child part, attach it with MapMode in the child part, and import that LCS into the sub-assembly. ...

Hi Zolko.
Thanks very much for your clear, detailed response last week.
I have now created a new tutorial to cover this topic:
https://github.com/thermalling/FreeCADA ... emblyTable

AssemblyTableComplete.png (9.9 KiB) Viewed 2152 times

TreeLegFootAssyImportedDatum.png (22.45 KiB) Viewed 2152 times

I really appreciate the work you are doing to improve FreeCAD as an effective engineering tool.