another sweep() question

I am unclear why this code results in a pristine cylindrical extrusion EXCEPT for one small place where it seems to twist frantically...

include <sweep.scad>

function f(a) = [18*sin(360*a), 18-18*cos(360*a*0.7),     36*sin(360*a/2)];

function shape(d) = let (dd = 5 * (1.2 - d/steps))
    [for (i=[1:10:360]) [dd*sin(i), dd*cos(i)]];

step = 0.005;
steps = 1/step;
path = [for (t=[step:step:1-step]) f(t)];
path_transforms = construct_transform_path(path);
sweep(shape(1), path_transforms);

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Thank you for recalling the thread so clearly!  Very helpful.  I did notice more than one "sweep.scad" on my computer, but was not able to recall why I should use one over the other.

Jon

@jon The original sweep.scad may show wild twists when the path gets a vertical (along z) step. This is discussed in http://forum.openscad.org/Twisty-problem-with-scad-utils-quot-sweep-quot-tc9775.html. There you will find also change suggestions to overcome that behavior. I have implemented those suggestions in a fork of sweep.scad and the results are far better. You may find my fork in https://github.com/RonaldoCMP/list-comprehension-demos. 

2018-01-05 12:55 GMT-02:00 jon <[hidden email]>:

I am unclear why this code results in a pristine cylindrical extrusion EXCEPT for one small place where it seems to twist frantically...

include <sweep.scad>

function f(a) = [18*sin(360*a), 18-18*cos(360*a*0.7),     36*sin(360*a/2)];

function shape(d) = let (dd = 5 * (1.2 - d/steps))
    [for (i=[1:10:360]) [dd*sin(i), dd*cos(i)]];

step = 0.005;
steps = 1/step;
path = [for (t=[step:step:1-step]) f(t)];
path_transforms = construct_transform_path(path);
sweep(shape(1), path_transforms);

-- 
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nor do I receive texts on my main phone number 
(which is a land line).  
If you know that I am on the road, please text me.  
If you know that I am home, please email me.

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-- 
Sent from my desktop computer.  
I do not receive emails while away from my desk, 
nor do I receive texts on my main phone number 
(which is a land line).  
If you know that I am on the road, please text me.  
If you know that I am home, please email me.