Thickness limitation?

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AlStu
Posts: 8
Joined: Fri Apr 24, 2020 2:10 pm
Location: Toronto, Canada

Thickness limitation?

Postby AlStu » Fri Apr 24, 2020 3:05 pm

I am making a suspiciously boatlike object. The attached file is a stripped down hull, no fillets, no chamfers, no decorations. In it, there is a pocket to hollow the hull. There seems to be an upper limit to the thickness of that pocket, related to the width of one sketch defining the hull body. The Sketch-Prow is 2mm wide with a quite acute angle from it. If I try a thickness above 1.7mm then it self-limits to what appears to be 1.7mm. I tried adding a structure just inside the prow so as to make the prow appear larger but no change. Suggestions?

Related, any hints on why the thickness appears periodically uneven?
ThicknessLimitation.PNG
Relevant region, Sketch-Prow selected, Thickness data shown.
ThicknessLimitation.PNG (28.82 KiB) Viewed 449 times
OS: Windows 10
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.18.4 (GitTag)
Build type: Release
Branch: releases/FreeCAD-0-18
Hash: 980bf9060e28555fecd9e3462f68ca74007b70f8
Python version: 3.6.6
Qt version: 5.6.2
Coin version: 4.0.0a
OCC version: 7.3.0
Locale: English/Canada (en_CA)
Attachments
Nonsuch 4.FCStd
(177.37 KiB) Downloaded 8 times
kisolre
Posts: 3158
Joined: Wed Nov 21, 2018 1:13 pm

Re: Thickness limitation?

Postby kisolre » Fri Apr 24, 2020 4:21 pm

Hello and welcome :)
In general OCC kernel (OpenCascade) that FreeCAD uses to perform those operation will not remove geometry on such operations. Other such operations are fillet and chamfer. Imagine a cube with 4mm side. If you want to chamfer two opposing edges of one side the maximum value allowed will be 1.99999 mm because at 2mm that side should be removed and OCC will not do that. Here the front face becomes smaller and smaller but wil not be removed by Thickness.
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Attachments
OCC face kept.JPG
OCC face kept.JPG (85.61 KiB) Viewed 440 times
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DeepSOIC
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Location: Saint-Petersburg, Russia

Re: Thickness limitation?

Postby DeepSOIC » Fri Apr 24, 2020 4:34 pm

works for me for values of at least 50 mm if I tick the checkbox "intersection".

OS: Windows 10 (10.0)
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.19.18234 (Git)
Build type: Release
Branch: master
Hash: 3af5d97e9b2a60823815f662aba25422c4bc45bb
Python version: 3.6.8
Qt version: 5.12.1
Coin version: 4.0.0a
OCC version: 7.3.0
Locale: Russian/Russia (ru_RU)
kisolre
Posts: 3158
Joined: Wed Nov 21, 2018 1:13 pm

Re: Thickness limitation?

Postby kisolre » Fri Apr 24, 2020 4:40 pm

DeepSOIC wrote:
Fri Apr 24, 2020 4:34 pm
works for me for values of at least 50 mm if I tick the checkbox "intersection".
PartDesign_Thickness speaks only about outwards intersection handling. I learned something new today :)
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AlStu
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Location: Toronto, Canada

Re: Thickness limitation?

Postby AlStu » Fri Apr 24, 2020 6:51 pm

kisolre wrote:
Fri Apr 24, 2020 4:21 pm
Hello and welcome :)
In general OCC kernel (OpenCascade) that FreeCAD uses to perform those operation will not remove geometry on such operations. Other such operations are fillet and chamfer. Imagine a cube with 4mm side. If you want to chamfer two opposing edges of one side the maximum value allowed will be 1.99999 mm because at 2mm that side should be removed and OCC will not do that. Here the front face becomes smaller and smaller but wil not be removed by Thickness.
.
Thanks, makes sense. The limit seems to be when a face converges to zero, it can't remove geometry. Although as you said, that is a software limitation because I can make a drawing for what I want and the machine shop can make it. I will try that end of the body in two parts: truncate to a wider section and patch in a kludged real end with 2mm width.
Always a pain learning new software - same concepts done differently with a whole new set of quirks. What is new for me is to not be able to define a point with 2D or even 3D coordinates but to use only constraints. Anything that floats my boat, I guess. See also next reply.
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AlStu
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Location: Toronto, Canada

Re: Thickness limitation?

Postby AlStu » Fri Apr 24, 2020 7:04 pm

kisolre wrote:
Fri Apr 24, 2020 4:40 pm
DeepSOIC wrote:
Fri Apr 24, 2020 4:34 pm
works for me for values of at least 50 mm if I tick the checkbox "intersection".
PartDesign_Thickness speaks only about outwards intersection handling. I learned something new today :)
Can I borrow your magic wand? FreeCAD locks up (no convergance) if Join Type is Intersection and Thickness >1.7mm. Can you post settings or screen captures and/or FCStd file?
kisolre
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Joined: Wed Nov 21, 2018 1:13 pm

Re: Thickness limitation?

Postby kisolre » Fri Apr 24, 2020 7:05 pm

AlStu wrote:
Fri Apr 24, 2020 6:51 pm
I will try that end of the body in two parts:
Did you read @DeepSOICs and mine last posts? It turns out I was not entirely correct and if you set the Thickness property "Intersection" to true your particular case works with more than 1,752.
edit: added screenshot.
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Thickness intersection.JPG
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DeepSOIC
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Re: Thickness limitation?

Postby DeepSOIC » Fri Apr 24, 2020 7:40 pm

AlStu wrote:
Fri Apr 24, 2020 7:04 pm
Can I borrow your magic wand?
Sure, it is named "FreeCAD v0.19" (apparently, the checkbox is not there in 0.18. "intersection" is a separate checkbox, not the item in join type dropdown list)
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AlStu
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Re: Thickness limitation?

Postby AlStu » Fri Apr 24, 2020 10:08 pm

The magic wand is version 0.19(PRE)!
Overly sturdy hull.png
Overly sturdy hull.png (27.89 KiB) Viewed 370 times
The 0.19 pre-release handles this well. Although I only want 3mm, it works at 20mm as in the pic above. Not being a full release, I will revert to 0.18 if 0.19 gives trouble. Thanks for all your help, both of you. BTW, is that SOIC as in the electronic component package? Much better than BGA :D .

OS: Windows 10 (10.0)
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.19.20655 (Git)
Build type: Release
Branch: master
Hash: e8e67e8c5ebbc9f9ed9ea67aba5b891969595ece
Python version: 3.8.2
Qt version: 5.12.5
Coin version: 4.0.0
OCC version: 7.4.0
Locale: English/Canada (en_CA)
kisolre
Posts: 3158
Joined: Wed Nov 21, 2018 1:13 pm

Re: Thickness limitation?

Postby kisolre » Fri Apr 24, 2020 10:18 pm

AlStu wrote:
Fri Apr 24, 2020 10:08 pm
I will revert to 0.18 if 0.19 gives trouble.
If it gives trouble just ask here and help make it better :)