Multi-part object, workflow question

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rabbit
Posts: 4
Joined: Fri Mar 17, 2017 2:59 pm

Multi-part object, workflow question

Postby rabbit » Mon Mar 20, 2017 4:55 pm

Hello,

I'm currently designing a device that starts as a single body. This is split into multiple bodies, which can then be assembled via dovetail joints. Something like this:

mod.png
mod.png (249.68 KiB) Viewed 155 times


Being new to FreeCAD, I made all the errors one can read about in this very forum, like forking the dependency graph and relying too much on external references in my sketches; and I suffered the consequences, having to re-draw stuff over and over.

So my question is: what is the recommended workflow for this type of design?

What I want to do:

  • Design the body as one piece, with parameters in a spreadsheet (this is 3D printed and dimensions will need tweaking to account for tolerances)
  • Design the split line/dovetail joint
  • Split the body into multiple parts
  • Continue to work on those parts, and have them change when the spreadsheet values change
  • Be able to use external references in my sketches, because they make life so much easier

From what I read, I should probably not use 0.17 for anything I'd might want to revisit, say, in a year's time, because things may change incompatibly.

My current understanding is that in 0.16, I'd better only have a single body in part design; so the plan is to make a master file with the main body and the spreadsheet, and then one file per split part, where I import the master via the Assembly2 workbench. In those files, I can "cut off" the parts I don't need and continue working with the component, and when I change the master, I can update the import via Assembly2.

Does that make sense, or are there better alternatives?

OS: Debian GNU/Linux 8.7 (jessie)
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.16.6707 (Git)
Build type: None
Branch: releases/FreeCAD-0-16
Hash: 5465bc47c95db45e0be85dc0e2872419efadce0f
Python version: 2.7.6
Qt version: 4.8.6
Coin version: 4.0.0a
OCC version: 6.8.0.oce-0.17
bejant
Posts: 4091
Joined: Thu Jul 11, 2013 3:06 pm

Re: Multi-part object, workflow question

Postby bejant » Tue Mar 21, 2017 1:29 am

Hi rabbit, and welcome!

rabbit wrote: I suffered the consequences, having to re-draw stuff over and over.

You didn't write how many things you've redrawn but you don't have to re-draw your Sketches; you can re-use them instead of starting again from scratch.

rabbit wrote:What I want to do:

Design the body as one piece,

I think I'd design the body as separate pieces from the start because to me it seems tat separating the whole into separate pieces later creates extra and unnecessary work.

rabbit wrote:Be able to use external references in my sketches, because they make life so much easier

Do you mean links to External Geometry (magenta geometry)? If so, my suggestion is to avoid using them (especially if you're going to use the Spreadsheet WB).

rabbit wrote:From what I read, I should probably not use 0.17 for anything I'd might want to revisit, say, in a year's time, because things may change incompatibly.

I agree, but you may want to try 0.17 anyway. In you didn't already know, you can have 0.16 and 0.17 installed on your system at the same time.

rabbit wrote:My current understanding is that in 0.16, I'd better only have a single body in part design;

In 0.16 we can have more than one solid on Part Design but these solids are usually unaware of one another. You can exploit this in your model if you wish by finishing one part of your model, mapping a new Sketch to a planar face in order to start the next piece in the correct location, then detaching the new Sketch (Part Design pull-down menu > Reorient Sketch tool, confirm that you want to detach the Sketch, then cancel to keep the newly detached Sketch at the original location).

Just my 2 cents worth of ideas...
My Part Design tutorials on YouTube (aimed at beginners).
rabbit
Posts: 4
Joined: Fri Mar 17, 2017 2:59 pm

Re: Multi-part object, workflow question

Postby rabbit » Tue Mar 21, 2017 7:39 am

bejant wrote:Hi rabbit, and welcome!

Thanks!

You didn't write how many things you've redrawn but you don't have to re-draw your Sketches; you can re-use them instead of starting again from scratch.

I was imprecise; of course I can reuse them, but often when I change something further up the tree sketches get broken and cannot be opened, and after using the "validate sketch" tool all external geometry links and constraints are gone, and re-applying them feels like completely redoing the sketch. :x

I think I'd design the body as separate pieces from the start because to me it seems tat separating the whole into separate pieces later creates extra and unnecessary work.

I suppose I could do so, even if it feels like redundant work.

I agree, but you may want to try 0.17 anyway. In you didn't already know, you can have 0.16 and 0.17 installed on your system at the same time.

I did play around with 0.17 a bit, and I like what I've seen with Part Design Next. Does it also lift the limitation on using external geometries in sketches?

In 0.16 we can have more than one solid on Part Design but these solids are usually unaware of one another. You can exploit this in your model if you wish by finishing one part of your model, mapping a new Sketch to a planar face in order to start the next piece in the correct location, then detaching the new Sketch (Part Design pull-down menu > Reorient Sketch tool, confirm that you want to detach the Sketch, then cancel to keep the newly detached Sketch at the original location).

I will definitely try that.

Thanks,

rabbit.
bejant
Posts: 4091
Joined: Thu Jul 11, 2013 3:06 pm

Re: Multi-part object, workflow question

Postby bejant » Tue Mar 21, 2017 3:15 pm

rabbit wrote:often when I change something further up the tree sketches get broken and cannot be opened, and after using the "validate sketch" tool all external geometry links and constraints are gone

That's why I try to avoid using Link To External Geometry. I mentioned reusing Sketches because some people don't know we can do that.

rabbit wrote:I did play around with 0.17 a bit, and I like what I've seen with Part Design Next. Does it also lift the limitation on using external geometries in sketches?

Yes (if I understand you correctly). In 0.17 you may want to create one of more master Sketches which define your geometry, and link things in you other Sketches to geometry in those master Sketches.
My Part Design tutorials on YouTube (aimed at beginners).
rabbit
Posts: 4
Joined: Fri Mar 17, 2017 2:59 pm

Re: Multi-part object, workflow question

Postby rabbit » Wed Mar 22, 2017 12:04 am

bejant wrote:That's why I try to avoid using Link To External Geometry. I mentioned reusing Sketches because some people don't know we can do that.


Just to be clear: I was talking about sketches that get broken that I then have to fix and partially redraw/re-constrain, while keeping them attached (or re-attaching them) to the same face.

Are you talking about something different, like using the same sketch for different operations? If so, how? I've made copies of sketches to use them that way (copy/paste in part design), is there another way?

rabbit.
bejant
Posts: 4091
Joined: Thu Jul 11, 2013 3:06 pm

Re: Multi-part object, workflow question

Postby bejant » Wed Mar 22, 2017 1:35 am

rabbit wrote:Are you talking about something different, like using the same sketch for different operations?

No. In Part Design we can't use a Sketch to create more than one Feature (but in the Part WB we can use a Sketch to create more than one thing).

rabbit wrote:I've made copies of sketches to use them that way (copy/paste in part design), is there another way?

You could try making one or more Draft WB > Clones of the Sketch, so if the original Sketch changes the Clones update.
My Part Design tutorials on YouTube (aimed at beginners).