Problems with Pad and Draft tools

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cehjan
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Problems with Pad and Draft tools

Post by cehjan »

I tried to draw the stove button you see in the picture. Not a complicated part, but very interesting.
2023-03-20_213607.jpg
2023-03-20_213607.jpg (23.06 KiB) Viewed 704 times
I will show one way of drawing which is impossible to draw this 3D model. I know there are other ways, but they are more complicated than this, and I think that one day FreeCAD must be able to draw this in such an elegant way. I have attached a 3D model.

Step 1: I rotated a quarter of the ellipse
Step 2: I made a pocket and beveled the face
Step 3: Using the Mirror command, I transferred the pocket operation to the other side.

This is where the problems start.
Step 4. With the Thickness command I created a thin-walled body. It only works with the Arc option, so fillets also appeared. They are a problem, but that problem can be solved.
Step 5: I drew the sketch and with the command Pad (Offset to face: To last) created the central cylinder. There is a problem here when the circle is so big that the extrusion touches those side surfaces.

You can somehow get here, but now a real problem appears.

Step 6: With the Draft command I tried to put a slope on the cylinder created in the last operation. Everything is OK until it touches those side surfaces.
2023-03-20_215224.jpg
2023-03-20_215224.jpg (57.17 KiB) Viewed 704 times
It is obvious that the commands Pad (Offset to face: To first, Up to face, To first) and Draft can only work with one face, as soon as they touch another face, problems arise. Situations like this often occur when modeling parts, and I'm wondering if there is some elegant solution to this problem, or FreeCAD is unable to do it.

You can also look at the example on the prismatic part where you can see that the Draft command works correctly while processing the middle face, and when it encounters oblique faces it behaves as if they do not exist.
2023-03-20_222438.jpg
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Shalmeneser
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Re: Problems with Pad and Draft tools

Post by Shalmeneser »

:idea:
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Capture d’écran 2023-03-20 231211.jpg
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cehjan
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Re: Problems with Pad and Draft tools

Post by cehjan »

Hi Shalmeneser, Thank you for the proposed solution.

I know how to draw this part, I wrote that it is not a problem.

I just wanted to point out the limitation that these commands have, hoping that they will be improved in the near future. Unfortunately, I'm too old to start learning programming, so I have to bore those who know how to do it. In the early 90's I had a Fortran exam in college 8-)
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Re: Problems with Pad and Draft tools

Post by drmacro »

cehjan wrote: Mon Mar 20, 2023 10:36 pm Hi Shalmeneser, Thank you for the proposed solution.

I know how to draw this part, I wrote that it is not a problem.

I just wanted to point out the limitation that these commands have, hoping that they will be improved in the near future. Unfortunately, I'm too old to start learning programming, so I have to bore those who know how to do it. In the early 90's I had a Fortran exam in college 8-)
The problems you refer to are in the OpenCASCADE 3D modeling engine used by FreeCAD. It is developed by the OpenCASCADE folks and FreeCAD has little, if any, sway on their developers. Since these issues have been the same for years, I doubt you can expect much change in them in the near future. :(
Star Trek II: The Wrath of Khan: Spock: "...His pattern indicates two-dimensional thinking."
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cehjan
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Re: Problems with Pad and Draft tools

Post by cehjan »

That's what I was most afraid of. So the kernel is the problem.

FreeCAD draws simple and medium parts nicely, but as soon as you get to complex parts, problems appear, mostly with the kernel. Plastic parts, pressed or cast parts can hardly be modeled without commands like Draft, Fillets, Thickness...

Unfortunately, the kernel is not among the best in the world. We can only hope that in the near future it will overcome its childhood ailments and that FreeCAD will soon take that last long step and become a normal 3D CAD program.
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thomas-neemann
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Re: Problems with Pad and Draft tools

Post by thomas-neemann »

I am of the opinion that what we humans really need: houses, machines, etc., freecad can do without any problems.
Gruß Dipl.-Ing. (FH) Thomas Neemann

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Re: Problems with Pad and Draft tools

Post by onekk »

cehjan wrote: Tue Mar 21, 2023 12:09 am ...
Unfortunately, the kernel is not among the best in the world. We can only hope that in the near future it will overcome its childhood ailments and that FreeCAD will soon take that last long step and become a normal 3D CAD program.
See maybe this article from one of OpenCascade develooers (and even a user on this forum).

http://quaoar.su/blog/page/introduction ... ng-kernels

It is fairly good in analyzing things about the actual state of the art of CAD kernels.

You will easily see that simply there is no other OpenSource CAD engine around that is not mesh based.

This blog is interesting as it show other interesting analysis on other things too.

Some tools have some problems, but some problems could be generated by the workflow.

I don't use Thickness tool, it is broken, it works mainly with uncomplicated surfaces, if you surface is complex, better to model it as a solid and then create the voids and subtract them.

Regards

Carlo D.
GitHub page: https://github.com/onekk/freecad-doc.
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thomas-neemann
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Re: Problems with Pad and Draft tools

Post by thomas-neemann »

onekk wrote: Tue Mar 21, 2023 6:43 am .... if you surface is complex, better to model it as a solid and then create the voids and subtract them.

...
+1
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cehjan
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Re: Problems with Pad and Draft tools

Post by cehjan »

Postby thomas-neemann » Tue Mar 21, 2023 7:18 am
I am of the opinion that what we humans really need: houses, machines, etc., freecad can do without any problems.
Every serious machine that needs to withstand a little more load is full of press-made parts, every household appliance is full of plastic parts, cast parts are all around us... Today, people are enthusiastic about new technologies (3D printing, Rapid prototyping, ...), but without classic mechanical engineering, the world would stop. All parts that are made in the mold must have sloping sides to be able to be removed from the mold, all loaded parts must have fillets to prevent stress concentration...

I am of the opinion that FreeCAD should be a serious software in the future and not a toy. Just as Blender has become powerful for 3D modeling, there should be a powerful free 3D CAD program in the 3D CAD field. FreeCAD has come the closest to that, and I hope they will take that final step quickly.

Onekk
See maybe this article from one of OpenCascade develooers (and even a user on this forum).
Thanks for the link. Excellent article.

I've been in the world of 3D CAD software for 25 years and I understand this problem about the kernel. Unfortunately, that is the reality. I just hope that in the future FreeCAD will transform from a 3D CAD program for enthusiasts to a normal and functional 3D CAD software that can be used by mechanical engineers as well.
Last edited by cehjan on Tue Mar 21, 2023 8:47 am, edited 1 time in total.
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papyblaise
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Re: Problems with Pad and Draft tools

Post by papyblaise »

very simply (for me :lol: )
file too large , just do a miror to finish it
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