B-Spline Extrude with thickness

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gsandy
Posts: 138
Joined: Sun Jan 27, 2019 7:07 pm
Location: Auckland New Zealand

B-Spline Extrude with thickness

Postby gsandy » Wed Oct 23, 2019 3:47 am

I have extruded a B-Spline aerofoil shape. How do I add a 0.5mm thickness to the inside of the extrusion to get a skin?


OS: Windows 7
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.18.16131 (Git)
Build type: Release
Branch: releases/FreeCAD-0-18
Hash: 3129ae4296e40ed20e7b3d460b86e6969acbe1c3
Python version: 3.6.6
Qt version: 5.6.2
Coin version: 4.0.0a
OCC version: 7.3.0
Locale: English/NewZealand (en_NZ)
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Wing 23-10-19.FCStd
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hammax
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Location: Ammersee

Re: B-Spline Extrude with thickness

Postby hammax » Wed Oct 23, 2019 4:50 am

… Offset -0,5mm
- compound of profile-sketch and offset
Have a look at the 3rd file and the modification possibility of the LE radius.

Wingt.PNG
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Wing 23-10-19_3.FCStd
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Wing 23-10-19_2.FCStd
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gsandy
Posts: 138
Joined: Sun Jan 27, 2019 7:07 pm
Location: Auckland New Zealand

Re: B-Spline Extrude with thickness

Postby gsandy » Wed Oct 23, 2019 7:05 am

Thanks Hammax. With both your 2nd and 3rd file sketches I cannot get the offset to work (using your files)!
If I create other sketches with lines or circle I can get the offset to work.
It is interesting that the TE of one is round and the other is straight, and they both work for you.
It it all to do with the "radius" the the LE?
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hammax
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Location: Ammersee

Re: B-Spline Extrude with thickness

Postby hammax » Wed Oct 23, 2019 5:09 pm

Hi Sandy,
… my FC-version is: Win10_32; FC_0.19.17300
Maybe our versions are not compatible???
I made a profile-sketch out of 2 sketcher-BSplines which are tangent at the LE.
That's "my normal" workflow for redrawn Data-profiles.
Those profile pairs can also be offsetted and cloned/scaled.
But this time the skin is made by boolean cut.

Wingt_2.PNG
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Wing 23-10-19_4.FCStd
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gsandy
Posts: 138
Joined: Sun Jan 27, 2019 7:07 pm
Location: Auckland New Zealand

Re: B-Spline Extrude with thickness

Postby gsandy » Wed Oct 23, 2019 8:24 pm

You were right Hammax it is my Windows version.
The only way I could get it to work was to make a B-Spline outer sketch. In the Draft WB make a polyline trace over the outer sketch. Offset this polyline inwards. Make a B-Spline inner sketch using the polyline as a guide. Extrude both sketches and then make a Boolean cut.
A bit long winded but it worked (the skin thickness wont be perfectly uniform but close enough).

Airfoil coordinates can be downloaded into an Excel spreadsheet, do you know if this data can be used in Freecad to generate sketch (in can in Solidworks, which I don't have)? This would save me drawing the two sketches, I would just import the two sets of coordinates!

Cheers Sandy.