Rotating 3d object

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Rotating 3d object

woodslanding
I am trying to create a shape that represents the space swept by moving a 3d
object around a hinge point.
<http://forum.openscad.org/file/t2632/rotate3Dobject.png>

I cannot figure out how to create this with 2D rotate_extrude operations....

Thanks in advance!
-eric



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Re: Rotating 3d object

thehans
Looks to me like sweeping that 3D object around in that way would just result in a cylinder, maybe with a small lip?  Not clear why exactly you'd want that.

On Fri, Nov 22, 2019 at 1:36 PM woodslanding <[hidden email]> wrote:
I am trying to create a shape that represents the space swept by moving a 3d
object around a hinge point.
<http://forum.openscad.org/file/t2632/rotate3Dobject.png>

I cannot figure out how to create this with 2D rotate_extrude operations....

Thanks in advance!
-eric



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Re: Rotating 3d object

woodslanding
the part has to be cut out such that the movement doesn't interfere with it.

I didn't give enough detail, sorry, but I approximated it, and it works.  



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Re: Rotating 3d object

kdtop

I would try something like this. 


widget();

module widget() {
  //pivot_offset = 2;
   
  for (angle=[0:1:90]) {  
    rotate([0,angle,0])  
    //translate([-pivot_offset,0,0])  
    angle_bracket();
  }  
}    

module angle_bracket(len = 50, thick = 3, arm_len = 15) {
   cube([len, arm_len, thick]);
   cube([len, thick, arm_len]);
}   

However, If you want a cylindrical shape, then I would recommend starting out by using cylinders.   If you zoom in, the rim of the above object has jagged edges.  I guess you could change the angle to 0.1 to make the jagged parts smaller. 

Kevin T

On Sat, Nov 23, 2019 at 2:37 AM woodslanding <[hidden email]> wrote:
the part has to be cut out such that the movement doesn't interfere with it.

I didn't give enough detail, sorry, but I approximated it, and it works. 



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Re: Rotating 3d object

doug.moen
You might be able to get the effect of sweeping a 3D shape around an axis of revolution by using the projection() module to convert the 3D shape to 2D, then using rotate_extrude() to perform the 2D profile. Whether you can find the right cut plane for the projection, in order to get the effect you want, will depend on the details of the 3D shape.

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Re: Rotating 3d object

thehans
Yeah Doug makes a good point about using projection, I was kinda thinking that but was being lazy to figure out how implement it.

But now I've made a generic module + example usage that should work for pretty much any shape I think:
And my solution to finding the right cut plane is to do all of them!
Note: It sweeps over [-90.+90] degrees, and assumes the object given to it is oriented such that the longer dimension is pointed towards the positive X-axis, and that it pivots about the Z axis, centered on the origin,.

Cheers,
Hans


On Sat, Nov 23, 2019 at 11:18 AM Doug Moen <[hidden email]> wrote:
You might be able to get the effect of sweeping a 3D shape around an axis of revolution by using the projection() module to convert the 3D shape to 2D, then using rotate_extrude() to perform the 2D profile. Whether you can find the right cut plane for the projection, in order to get the effect you want, will depend on the details of the 3D shape.
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Re: Rotating 3d object

MichaelAtOz
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Hans, very nice, and surprisingly not too resource hungry.



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Re: Rotating 3d object

MichaelAtOz
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(sorry - checking on a problem someone has replying to this, testing two two
two...)



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Re: Rotating 3d object

Ian Nichols
In reply to this post by woodslanding
On Sat, 23 Nov 2019 at 07:37, woodslanding <[hidden email]> wrote:
the part has to be cut out such that the movement doesn't interfere with it.

I didn't give enough detail, sorry, but I approximated it, and it works.  


Ah, I see.  In that case, what I would do is get out a calculator and work out the diagonal of one of the largest faces of your angle bracket & make a cylinder with that radius and height equal to the thickness of the bracket extrusion.  Then make another cylinder with a radius equal to the diagonal of one of the smallest faces (i.e. the edge of the extrusion) with a height equal to the overall width of the bracket.  The union of those two is the shape you want.  You may need to modify this depending on your chosen rotation axis ;)

Hope that makes sense.

Ian
 
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