Struggle with .step or .stl workflow

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zeuser
Posts: 5
Joined: Sun Nov 22, 2020 4:39 am

Struggle with .step or .stl workflow

Post by zeuser » Sun Nov 22, 2020 5:04 am

Hi all,

I've been trying to figure out a working workflow for how to modify some existing models. The .stl and .step file can be found here: https://github.com/Bemeier/bmek/tree/ma ... BottomCase

I tried using the following workflow to get the .stl file into a good state:
1. import the file
2. Using the Part workbench, convert it to a shape
3. Refine shape
The issue I run into with this workflow is the side of this model with the logo on it doesn't get cleaned up properly - the flat parts are still a series of triangles.

I tried the following for the .step file:
1. import the file
2. Using the PartDesign workbench, convert to body
What I'm stuck on here is what to do next. I tried extruding the logo for example, and I get a "No shape selected" warning.


What I need help with is getting the object into a state where I can begin editing it. For reference if it helps, two of the edits I want to make are clearing off the logo and modifying the rounded rectangle cutout on the opposite face.


FreeCAD version info:
OS: macOS 10.15
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.18.16146 (Git)
Build type: Release
Branch: (HEAD detached at 0.18.4)
Hash: 980bf9060e28555fecd9e3462f68ca74007b70f8
Python version: 3.6.7
Qt version: 5.6.2
Coin version: 4.0.0a
OCC version: 7.3.0
chrisb
Posts: 30620
Joined: Tue Mar 17, 2015 9:14 am

Re: Struggle with .step or .stl workflow

Post by chrisb » Sun Nov 22, 2020 8:55 am

Before you can work on an STL with the usual tools such as booleans or the PartDesign tools you have to convert the shape to a solid. This is done in Part workbench (see the menu).

Such a solid, and it's the same with an imported step can be seen as a base block with nothing more than faces, edges and vertices. You cannot change any of these (exception: see below).
But you can well add and subtract material. So after having created a body with the STEP as BaseFeature you can add sketches and create pads and pockets.

If you only want to remove things from the solid, you can use Part->Defeaturing. Be warned that this is not parametric.
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.
zeuser
Posts: 5
Joined: Sun Nov 22, 2020 4:39 am

Re: Struggle with .step or .stl workflow

Post by zeuser » Sun Nov 22, 2020 1:44 pm

Thanks chrisb!
chrisb wrote:
Sun Nov 22, 2020 8:55 am
But you can well add and subtract material. So after having created a body with the STEP as BaseFeature you can add sketches and create pads and pockets.
I do have a sketch mapped to a face once I have a body from the .step file. I don't know how to then take a feature from that existing body (circular cutout for example) and generate a shape in the sketch based on it. Thats the big gap for me preventing me from creating pads or pockets.
chrisb
Posts: 30620
Joined: Tue Mar 17, 2015 9:14 am

Re: Struggle with .step or .stl workflow

Post by chrisb » Sun Nov 22, 2020 2:35 pm

You should first learn the very basics. Look at the PartDesign Tutorials, they will show you what you need to get going.
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.
openBrain
Posts: 5154
Joined: Fri Nov 09, 2018 5:38 pm

Re: Struggle with .step or .stl workflow

Post by openBrain » Sun Nov 22, 2020 2:44 pm

Would that help ?
phpBB [video]
zeuser
Posts: 5
Joined: Sun Nov 22, 2020 4:39 am

Re: Struggle with .step or .stl workflow

Post by zeuser » Sun Nov 22, 2020 4:42 pm

Both of what you guys linked me to does help. For the kinds of things I'm trying to do, what are all the workflows/tools I should work through tutorials for? I'd be happy to step away and read up/practice, I've been struggling with not knowing terminology and where to start.
drmacro
Posts: 2322
Joined: Sun Mar 02, 2014 4:35 pm

Re: Struggle with .step or .stl workflow

Post by drmacro » Sun Nov 22, 2020 5:57 pm

zeuser wrote:
Sun Nov 22, 2020 4:42 pm
Both of what you guys linked me to does help. For the kinds of things I'm trying to do, what are all the workflows/tools I should work through tutorials for? I'd be happy to step away and read up/practice, I've been struggling with not knowing terminology and where to start.
This is my $.02...it's probably worth less. :lol:

You are attempting to use geometry created in a way that is not native to FreeCAD. Once it is converted to a form FreeCAD can interact with, i.e. a solid, then FreeCAD can cut away or add, but can't change it's inherent shape. So, even then you need to understand how to use the native tools that add and cut away.

Learning to use a new, complex tool, with information, foreign to FreeCAD, is going to be an up hill battle. Knowing how the tool works in it's native way is essential. (I.e. learn to walk before entering a marathon so to speak...)

There are plenty of folks on Youtube showing the use of imported geometries. I'm not sure there is any one that captures all the subtleties.

To actually get a basic intro of how, at least, the Part Design workbench can be used, try the intro that is listed in my signature below.
(Not implying it has any instruction about imported (step or otherwise) geometry, just FreeCAD basics.)
Star Trek II: The Wrath of Khan: Spock: "...His pattern indicates two-dimensional thinking."

My beginners, written treatise: Learning FreeCAD
heda
Posts: 145
Joined: Sat Dec 12, 2015 5:49 pm

Re: Struggle with .step or .stl workflow

Post by heda » Sun Nov 22, 2020 6:37 pm

another 2 cents...

i would say stl is just for rendering, or modelling for purpose of rendering, i.e. computer graphics
step is a more design like format - but not really for editing either - main practical purpose is interchanging dead models, but this time with continuous surfaces - so the format works when that is important (read any manufacturing industry).

for an editable file - unfortunately one is stuck with the software it was created on - it kind of sucks, but not much to do about it.

if you are looking at doing things as in the video - your best bet is then modeling from scratch - does not take that long and you have it fully editable, your main use of the step in that case is to just take measurements off it, and compare so that they are the same when you are done.

what tutorial? any tutorial that gets you going towards a complete remodeling from scratch, most people recommend part design for that.
once you can do some modeling from scratch - you either feel comfortable enough to just do it from scratch, or you will know enough to find your way of how to start using donor models.
zeuser
Posts: 5
Joined: Sun Nov 22, 2020 4:39 am

Re: Struggle with .step or .stl workflow

Post by zeuser » Sun Nov 22, 2020 7:02 pm

Thanks All! I was starting to come to the conclusions you guys are drawing. I may try either using the reverse engineering tools, or asking the creator of the designs for measurements and trying to recreate the files.

By any chance, are any of the other supported filetypes easier to work off? I can maybe ask the creator to share those with me if they are able.
drmacro
Posts: 2322
Joined: Sun Mar 02, 2014 4:35 pm

Re: Struggle with .step or .stl workflow

Post by drmacro » Sun Nov 22, 2020 7:11 pm

I would agree that stl is pretty much only good for tracing over.

STEP on the the other hand can be more useful, though, still not as useful as modeling from scratch.

For example, this is the STEP model imported into FreeCAD:
Snip macro screenshot-a9e008.png
Snip macro screenshot-a9e008.png (40.58 KiB) Viewed 75 times
Adding a boss is almost trivial in Part Design:
Snip macro screenshot-698ab4.png
Snip macro screenshot-698ab4.png (52.44 KiB) Viewed 75 times

Or extract the face of the object to get a sketch with all the pertinent geometry:
Snip macro screenshot-b8bc40.png
Snip macro screenshot-b8bc40.png (62.75 KiB) Viewed 75 times
Then make your additions and simply Pad:
Snip macro screenshot-af8984.png
Snip macro screenshot-af8984.png (59.67 KiB) Viewed 75 times
Since an STL file is a bunch of triangle connected together to look like the model, this would be more difficult. But, actual faces in a STEP do have some advantages.
Star Trek II: The Wrath of Khan: Spock: "...His pattern indicates two-dimensional thinking."

My beginners, written treatise: Learning FreeCAD
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