Sketches on curved surfaces

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jgauthier
Posts: 22
Joined: Fri May 07, 2021 9:02 pm

Sketches on curved surfaces

Post by jgauthier »

Using FreeCAD 0.19, I understand that starting a sketch on a non-planar face doesn't work.

In this model, I've basically tacked on primitives to get the job done. But I'm wondering if there's more of a 'sketch' way to do it.
With the 'arms' I realize I could make a square, on top, and use the "hole in a cylinder method" (https://forum.freecadweb.org/viewtopic. ... t=0#p30704)

However, I am not sure how to make the 'bumps'. I haven't figured out a way to pad/extrude a sketch into a sphere.
2021-05-12_8-38-21.png
2021-05-12_8-38-21.png (39.4 KiB) Viewed 1189 times
PCR
Posts: 44
Joined: Wed Apr 21, 2021 1:07 pm

Re: Sketches on curved surfaces

Post by PCR »

you can revolve?
PCR
Posts: 44
Joined: Wed Apr 21, 2021 1:07 pm

Re: Sketches on curved surfaces

Post by PCR »

like this?
Attachments
sphere.FCStd
(18.49 KiB) Downloaded 36 times
jgauthier
Posts: 22
Joined: Fri May 07, 2021 9:02 pm

Re: Sketches on curved surfaces

Post by jgauthier »

Oh, that's a good idea! I'll try it later today!
Bance
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Re: Sketches on curved surfaces

Post by Bance »

jgauthier wrote: Wed May 12, 2021 12:47 pm Using FreeCAD 0.19, I understand that starting a sketch on a non-planar face doesn't work.
If you don't want your model to break, starting a sketch on a face is a very bad idea. Use the std planes and add offsets, with expressions for parametrics.
jgauthier
Posts: 22
Joined: Fri May 07, 2021 9:02 pm

Re: Sketches on curved surfaces

Post by jgauthier »

Bance wrote: Wed May 12, 2021 2:10 pm
jgauthier wrote: Wed May 12, 2021 12:47 pm Using FreeCAD 0.19, I understand that starting a sketch on a non-planar face doesn't work.
If you don't want your model to break, starting a sketch on a face is a very bad idea. Use the std planes and add offsets, with expressions for parametrics.
Not sure I follow, but I am also still figuring things out. By "std planes" do you mean a single sketch, making edits to the sketch?
I'm confused about how to do with with varying heights necessary. Is there a tutorial about this I can read about?

Edit: Also, I learned by doing this and watching this. Are you saying this tutorial is doing things 'very bad'?
https://wiki.freecadweb.org/Basic_Part_Design_Tutorial
drmacro
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Re: Sketches on curved surfaces

Post by drmacro »

Star Trek II: The Wrath of Khan: Spock: "...His pattern indicates two-dimensional thinking."
jgauthier
Posts: 22
Joined: Fri May 07, 2021 9:02 pm

Re: Sketches on curved surfaces

Post by jgauthier »

Thanks for that. I read through the problem, and ways to avoid it. Since my design is simple, and not very far into it, I will adjust the way I am doing this and use datum planes.
drmacro
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Re: Sketches on curved surfaces

Post by drmacro »

datum planes not required, typically, just sketch attachment offsets.
Star Trek II: The Wrath of Khan: Spock: "...His pattern indicates two-dimensional thinking."
Bance
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Location: London

Re: Sketches on curved surfaces

Post by Bance »

You can do it like this:-
Attachments
Example.FCStd
(84.79 KiB) Downloaded 41 times
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