Help placing and joining parts in Assembly4

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robertmain
Posts: 44
Joined: Mon Nov 04, 2019 3:34 am
Contact:

Help placing and joining parts in Assembly4

Post by robertmain »

So, I'm trying to assemble a (somewhat) complex model in Assembly 4.

I'm placing LCS at points where I want to join the parts kind of like push pins (this is my understanding of how assembly is meant to work, please correct me if I'm wrong) and I'm running into a few issues:
  1. When attaching two parts together, I want to attach them using an expression to calculate the axis offsets. When I go into the attachment editor and fill the expression in, the expression evaluates to the value I expect and looks like it worked, but when I click "OK" on the expression editor, the value is overridden by "0" and the part goes back to the base LCS on the parent object. If I look under ""Placement" in the properties pane, I see my value still there greyed out, but "0mm" in black like it's being overridden
  2. I can seemingly only set one axis by expression. The first axis I set works, any subsequent ones allow me to write the expression but then evaluate to "0mm" again

Code: Select all

OS: Debian GNU/Linux 10 (buster) (GNOME/gnome)
Word size of FreeCAD: 64-bit
Version: 0.20.29177 (Git) AppImage
Build type: Release
Branch: (HEAD detached at 0.20)
Hash: 68e337670e227889217652ddac593c93b5e8dc94
Python 3.9.13, Qt 5.12.9, Coin 4.0.0, Vtk 9.1.0, OCC 7.5.3
Locale: English/United States (en_US)
Installed mods: 
  * fasteners 0.4.4
  * Assembly4 0.12.3
Attachments
Cabinet Door.FCStd
Door part
(19.93 KiB) Downloaded 20 times
Door Bracket.FCStd
Bracket part
(27.51 KiB) Downloaded 21 times
Trash cabinet.FCStd
Cabinet part
(75.95 KiB) Downloaded 25 times
Trash Cupboard Assembly.FCStd
Master assembly
(13.42 KiB) Downloaded 21 times
Trash Rail.FCStd
Rail part
(22.07 KiB) Downloaded 21 times
PAS_Drafter
Posts: 338
Joined: Mon Aug 02, 2021 6:29 am
Location: California, USA

Re: Help placing and joining parts in Assembly4

Post by PAS_Drafter »

Are you adding the expression to the Placement section or the Attachment section? See the screen shown below.


Attachment.PNG
Attachment.PNG (24.92 KiB) Viewed 628 times


My experience is that you must put the expression in the Attachment section for it to take effect. I mistakenly put them in the Placement section myself in the past and experienced what you did. It drove me mad until I figured out not to do that.
robertmain
Posts: 44
Joined: Mon Nov 04, 2019 3:34 am
Contact:

Re: Help placing and joining parts in Assembly4

Post by robertmain »

Good call! I've tried both and the attachment (as you rightly pointed out) seems to work(sometimes) where the "Placement" section doesn't. However, using the attachment section I can only set one axis. The others are just ignored...

EDIT: Also - am I using/have I understood LCSs correctly? i.e: LCS at each point you want to join together...almost like rivets
PAS_Drafter
Posts: 338
Joined: Mon Aug 02, 2021 6:29 am
Location: California, USA

Re: Help placing and joining parts in Assembly4

Post by PAS_Drafter »

robertmain wrote: Mon Oct 03, 2022 12:25 pm EDIT: Also - am I using/have I understood LCSs correctly? i.e: LCS at each point you want to join together...almost like rivets
LCS can be used in a number of ways. It is simply a point you set on one part that you know the relative position to that you can match to a point on another part you know the relative position to that you want to match up. The points do not have to be where the pins are or even holes. They can be any place you want them to be. However, if you have two holes that need to line up, that is the easiest to do. However, you can also set up a specific edge that you want to join that has no hole or pin. The trick is just to make sure you have the proper points on both parts identified.

You should be able to set those positions with expression from a spreadsheet or other value so that the LCS moves and thus moves the part if you make changes. I've never had a problem where the Attachment point won't let me set a position, even if I'm assigning all three axis and all three rolls.

It would help me to try and duplicate the problem if you could give me the exact LCS you are trying to line up and what values you are trying to link to an expression.
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