Converting model aircraft plans into a 3D model for printing

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NormandC
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Re: Converting model aircraft plans into a 3D model for printing

Postby NormandC » Sun Jun 03, 2018 4:44 am

TonyR wrote:
Sun Jun 03, 2018 1:55 am
And that's where it all stops - no drawing tools are available. Everything is greyed-out...
You only switched workbenches. Now you need to create a sketch. Click on the left most icon Image and select a plane parallel to the one you created the image plane on. I recommend adding a small offset in the "Select orientation" dialog so the sketch does not lie on exactly the same plane as the image, but rests above it.

This will enter you into sketch editing mode where the sketching and constraining tools will be active.
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TonyR
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Re: Converting model aircraft plans into a 3D model for printing

Postby TonyR » Sun Jun 03, 2018 9:20 am

Thanks NormandC - slowly getting somewhere now, thanks to everyone's kind help.

I can create a sketch - it's a bit rough at the moment - I'm guessing that I can centre it perfectly on the Sketch grid.. and make things much neater. But that's for later. I'm just trying to learn the basics here, and I can clean things up further down the track.

Ok... I used a 'periodic B-spline'. Is that the right one? Once I join it all up, I notice that there's two red dots per point. I don't really understand what that means right now, but at least I'm able to trace around my Former.
FreeCAD07.jpg
FreeCAD07.jpg (109.87 KiB) Viewed 484 times

Once I have closed the loop, and pressed the little button up in the top right corner:
FreeCAD08.jpg
FreeCAD08.jpg (5.7 KiB) Viewed 484 times

I see this extra info - not really sure what that means either:
FreeCAD09.jpg
FreeCAD09.jpg (110.09 KiB) Viewed 484 times

I'll get cracking on doing the second former, and try to use the Loft tool to 'extrude' my shape. Once I've done that, how do I tell it that it should be a hollow shape with 2mm thick walls, and not a solid truncated cone?
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NormandC
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Re: Converting model aircraft plans into a 3D model for printing

Postby NormandC » Sun Jun 03, 2018 5:05 pm

TonyR wrote:
Sun Jun 03, 2018 9:20 am
I used a 'periodic B-spline'. Is that the right one?
I think so. The B-spline tool creates an open curve. The Periodic B-spline creates a closed one.

TonyR wrote:
Sun Jun 03, 2018 9:20 am
Once I join it all up, I notice that there's two red dots per point.
The difference is
  • Control points are outside the curve, and joined by green lines which we call the control polygon. These control points are used to control the shape of the curve. Each also has a blue circle around it. It is an option to affect the weight of the control point. By default all circles are of identical radius. But if you delete the equality constraint between the circles, you'll be able to resize the circles independently. They will work like gravity: a bigger circle will pull the curve toward itself. But I recommend you don't work with this. Working with B-splines is complex enough without adding another level of complexity.
  • Knots are points lying on the curve and are currently non-editable.
TonyR wrote:
Sun Jun 03, 2018 9:20 am
I see this extra info - not really sure what that means either:
This is the curvature comb. It's used to visualize the curvature of the B-spline. I don't work with B-splines much so I can't tell more.

TonyR wrote:
Sun Jun 03, 2018 9:20 am
try to use the Loft tool to 'extrude' my shape. Once I've done that, how do I tell it that it should be a hollow shape with 2mm thick walls, and not a solid truncated cone?
There is a tool named Part Thickness to create a thick shell out of a solid. But to be honest, it's rather unreliable and fails often. I'm honestly not confident it will work well with lofted B-splines... It might work, but don't get your hopes too high... You could also loft a surface rather than a solid, then use Part Offset (the 3D one) to give it thickness. I think it relies on the same fragile algorithms as the Thickness tool though.
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NormandC
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Re: Converting model aircraft plans into a 3D model for printing

Postby NormandC » Sun Jun 03, 2018 5:14 pm

I just tried a Part Thickness on a solid Loft made from two periodic B-splines. FreeCAD crashed...

EDIT: made a surface loft, tried 3D Offset... Instant crash!
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NormandC
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Re: Converting model aircraft plans into a 3D model for printing

Postby NormandC » Sun Jun 03, 2018 5:21 pm

You will have to test the process. From the few minutes I spent, you might be better using the plain open B-spline instead, and close it into itself. Only with it was able to get a result with Part Thickness.
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TonyR
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Re: Converting model aircraft plans into a 3D model for printing

Postby TonyR » Mon Jun 04, 2018 3:21 am

Fantastic info NormandC :mrgreen:

Wow! Sooo much still to learn...