Helix Sweep

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gsandy
Posts: 240
Joined: Sun Jan 27, 2019 7:07 pm
Location: Auckland New Zealand

Helix Sweep

Postby gsandy » Tue Sep 14, 2021 11:40 pm

I am trying to model a shaped blade, as shown in screenshot attached, which is on a helix sweep. Any suggestions would be appreciated.


OS: Windows 10 (10.0)
Word size of FreeCAD: 64-bit
Version: 0.20.25429 (Git)
Build type: Release
Branch: master
Hash: acce57a25d82b0408fa07b9452ed31c8a06c7a1b
Python version: 3.8.10
Qt version: 5.12.9
Coin version: 4.0.0
OCC version: 7.5.2
Locale: English/New Zealand (en_NZ)
Attachments
Forum Screenshot.jpg
Forum Screenshot.jpg (32.92 KiB) Viewed 545 times
Forum Helix 15-9-21.FCStd
(10.3 KiB) Downloaded 15 times
chrisb
Posts: 37122
Joined: Tue Mar 17, 2015 9:14 am

Re: Helix Sweep

Postby chrisb » Tue Sep 14, 2021 11:47 pm

I guess that it is only caused by the perspective distortion of the photo that the helix looks thicker in the middle.

For such a helic you need only one of the helices, e.g. the outer.
- create a sketch in XY plane with a section of the helix
- attach it to the helix with mode Frenet NB
- create a sweep with the section and the helix
- mirror the sweep
- make a union of the sweeps and the center.
A Sketcher Lecture with in-depth information is available in English, auf Deutsch, en français, en español.
gsandy
Posts: 240
Joined: Sun Jan 27, 2019 7:07 pm
Location: Auckland New Zealand

Re: Helix Sweep

Postby gsandy » Wed Sep 15, 2021 12:15 am

Its not a distortion, the blade is thicker in the middle.
The only reason the inside helix is there is because I was trying solve the problem by creating an inside and outside "airfoil" shape and make an extrude on two rails (from outside to inside airfoil).
chrisb
Posts: 37122
Joined: Tue Mar 17, 2015 9:14 am

Re: Helix Sweep

Postby chrisb » Wed Sep 15, 2021 5:03 am

A two rail sweep exists in addon Curves workbench.
A Sketcher Lecture with in-depth information is available in English, auf Deutsch, en français, en español.
gsandy
Posts: 240
Joined: Sun Jan 27, 2019 7:07 pm
Location: Auckland New Zealand

Re: Helix Sweep

Postby gsandy » Wed Sep 15, 2021 5:39 am

That's the one I tried but could not get to work. I could create the two rails but could not create the right inner and outer profile sketches.
chrisb
Posts: 37122
Joined: Tue Mar 17, 2015 9:14 am

Re: Helix Sweep

Postby chrisb » Wed Sep 15, 2021 7:37 am

You may have to create two sweeps, both based on slightly different 3D parametric curves (addon macro).
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papyblaise
Posts: 4101
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Location: France

Re: Helix Sweep

Postby papyblaise » Wed Sep 15, 2021 9:06 am

you research the dimensions of the heliptical parts, you place them on planes tangent to the hub, in the middle and tangent to the outside diameter
you make a loft, then a common with a cylinder with the outside diameter
it is a rustic propeller for river transport boat or canal with a low efficiency due to strong cavitation because of this little tapered shape
Attachments
helice.FCStd
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helice.PNG
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gsandy
Posts: 240
Joined: Sun Jan 27, 2019 7:07 pm
Location: Auckland New Zealand

Re: Helix Sweep

Postby gsandy » Wed Sep 15, 2021 7:57 pm

Thanks papyblaise you have given me a clue on how to proceed. I will work on it today. Cheers Sandy

Thanks Chrisb I will investigate 3D parametric curves (addon macro).
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