Hello to everbody. We previously discussed some methods for developing a spiral. Now I'm going to explain how it's possible to make a coil spring which is tightly wrapped at the ends, and loosely wrapped in the middle:
1) Make a vertical "Curve Through Points", while snapping to these points:
0,0,0
0,0,1
0,0,2
0,0,3
0,0,4
0,0,5
0,0,6
0,0,7
0,0,8
**You can use any odd # of points for this technique to work. But i find it works best with 7, 9, or 11 points. For this example we are using 9 points to build the curve**
1) Use the "Schbeurd-Shorty Spiral" method explained in previous thread to build a 360 degree rotation of a spiral which wraps around the curve from step #1. You should follow my trimming method as explained in post # 277.13, so the segment will be G1 at both ends.
http://www.moi3d.com/forum/index.php?webtag=MOI
2) Once you have the spiral segment, you make copies by snapping end to end in the Z axis, until you have as many rotations as you desire for the coil spring. Join those segments into a polycurve, and then scale in Z axis, so the height exactly matches the vertical curve.
3) Now create a surface between the spiral and the vertical curve by using Loft with History enabled.
4) Select the vertical curve, and Show Points. Select the points # 0-1-2-3. Choose the Scale3D tool and then scale to factor of .25, snapping at the location of point # 0... Deselect those points, and then select the points # 5-6-7-8. Choose the Scale3D tool and then scale to factor of .25, snapping at the location of point # 8. You will notice the Loft surface is deformed, being pulled at both ends.
5) Now draw a circle at the end of your vertical curve. This circle must have a smaller diameter than your coil. extrude this curve in Z axis until the extrusion is longer than your coil. Move the new extrusion vertically until both ends are obviously "sticking out" of the coil top and bottom.
6) Select the Lofted surface from step #3. Then select the "trim" tool. Then select the extrusion surface as your cutting object. Trim away the section of the lofted surface which is sticking out from the cutting surface.
7) now you can see the lofted surface from step #3 has an edge which appears tightly wrapped at the ends, and loosely wrapped in the middle. Select those edges one by one until you've got all of them highlighted. Then Copy/Paste to create a new curve, and join them. Invert selection, and hide all.
8) The last part is only to create the thickness for the coil spring. To do this quickly and accurately (without self-intersections) requires only a very simple trick. Create a line, first by snapping to the end of the coil, and then snapping to the nearest rotation of the coil by using the "Perp" Object snap. Now draw a circle, by first snapping to the end of the coil, and then snapping the radius to the "Mid"point of the short polyline you've just drawn before. select that circle, and sweep along the coil spring curve.
If you want to make a coil spring which is tightly wrapped at the middle and loosely wrapped at the ends, then just go back to step # 4 and scale the points # 1-2-3-4-5-6-7 while using the location of point # 4 as the origin...
You're all done with this tutorial :) I hope some people found this to be helpful. If you notice any mistakes, or have suggestions on improving the methods described here, please let me know...
Thanks,
jonah (shorty)
