Helix Construction Help!



Jake here, first post on the forum, been using Sketchup on and off for ~5 years, but this is the first time I’ve needed real help.

So I’m working on a model that has a complex double-helical structure, and the first portions of each helix were relatively straight-forward: using circles as guides to draw the necessary lines. The last segment of the helix is driving me crazy though–as you can see, the form opens up in a gradual curve, so evenly spaced circles won’t work. To get that top line, I unfolded a semicircle into a straight line, placed the connecting segments at each end, put a tangential arc between them, and then curved that tangent around the circle [If that makes no sense, I can try to explain it with more pics.] Time consuming (even more than normal), to say the least.

What I’m wondering is this: is there any quicker way of doing this, or am I going to be stuck in modeling purgatory for a while? The final intention is a human-scale additive manufactured prop, so it has to be exact.

(Worthless bonus points to anyone who can guess what this is going to be :wink:)


I’m guessing this isn’t very big. Try working at a scale of 10 or maybe 100 times larger and then scale down.

I’d probably use Curviloft or TIG’s Extrude Tools with the helical paths and a profile at each end. It would be easier to to tell for sure if we could see the entire SKP file.



Final is 80 inches (I said human-scale), broken down into three segments–hunting industrial printers that can run it. Here’s a pic of the entire helical section; it’s all a constant cross-section profile until this last bit. I’ll look into those extensions now.

And yeah, the rest of the helix, plus two screw thread sections (male and female for each) were all done manually ¯_(ツ)_/¯ Stubborn one, this


@DaveR I think Curviloft is going to get me close enough, or at least take a lot of the gruntwork out. Thanks!


Helical modeling - tutorials, both manual and with plugins and links to the plugins.


If it is just the transition that you need, I made this with TIGs [Extrude Tools]


Hey there! Do you have a bone-line? If you can draw the central spline of the helix and if the section cut profile of your model is constant, you could possibly try the Eneroth Upright Extruder.


I’m still not clear as to the shape you’re looking for, but you might take a look the Spirix plugin. For example, revolving a circle while scaling it larger while increasing z with a parabolic function and increasing linear radial expansion gives this:


I ended up using Curvisoft to generate the “ribs” and I’m connecting them manually. I probably could have done the entire thing in Curvisoft, but the UI takes some learning, and I was getting impatient. It’s the gradual transition from the cross-section at the bottom to the elongated cross-section at the top that was catching me—free drawing wasn’t coming out right; if you look at the original pic I posted, you can see they’re both complex polygons (16-sided, I think), with no real verticals or good reference points.