One rail extrude

hello! I have to do a sort of pipe, along one rail, which is curved, but with a bigger section at the beginning than at the end… if I do the one rail extrude with only one section, it’s without problem… as soon as I ask for two sections, there is a strange narrow shape in the middle of the extruded shape… how to get a progressive, narrowing gently, shape??
thank you for help!

Could you post a file?

yes, but I don’t understand how to upload a JPG, on this site!
basically, think about a “C”, like a pipe, with a bigger round section at the beginning of the “C”, and a smaller one at the end… The “C” curve is the rail, and two circles the cross section… but impossible to get a clean shape! (for me!)

Perhaps you can post the file so we can see what’s happening. Note that you are mixing your terminology (and perhaps that is the problem), you either SWEEP (1 or 2 rails) or you EXTRUDE (perhaps along a curve). There is a great difference in how these act. Extrude keeps the profile(s) parallel to the original at all times. Sweeps try to orient the profile to the rail, with a number of options to control the orientation along the sweep. You can extrude multiple curves at once into several surfaces/polysurfaces, but the sweeps form only one object at a time, all sections must be successive and become part of the same object.


Don’t upload a jpg, upload your 3dm. Just drag and drop it into your post somewhere in a blank space.

thank you for your help! I try to upload the 3dm file!..paille.3dm(1.9 MB)

paille.3dm(1.9 MB) whowww, that works!!!

just try to do a one rail on the “c” curve, getting the cross sections 1 and 2, and getting a progerssive shape… I don’t know if you are going to have the background JPG, in this file… because it aws the rally shape I was after, but seems more complicated!

Is this what you want? Just Sweep1, select the rail, then the two circles, use options Freeform and do not check global shape blending, then OK…


Note: you can also use the Pipe command with the C curve and then just specify the start and end diameters…

paille-s.3dm(2.1 MB)

damned!!! I didn’t get at all the good shape! I join the result!..paille2.3dm(2.0 MB)

but whith the pipe command, it’s perfect!! thank you!!!
would you, please, let a glance at this JPG? it’s that shape of candy I try to get… with the two helocoidals shape, the red and the white, grouped in one
maybe you find how it’s possible to get that shape in geometry? (I mean, not by textures)… I don’t see at all; how to do!
thank you really for your time!!

Well, texturing is really the way to go, but you can achieve the effect you want more or less with surfaces - it’s a bit complex for a beginner though…

  1. Create your pipe
  2. Start the command Spiral, with the option “around curve”, pick the same curve you made the pipe with.
  3. Give it a number of turns (I used 6 in the example). For the first radius, use the “quad” objec smap and snap to one quadrant of the lower circle, then for the second radius snap the corresponding quad on the upper end.
  4. Make another spiral snapping to the opposite quads - in other words turned 180° from the first.
  5. Use the command Pull to pull the spirals to the pipe surface, delete input=yes.
  6. Split the pipe surface with the spirals.
  7. Start joining the surfaces back up along the spiral, you may need to explode the ends and join them separately. you should end up with two spiral bands.
  8. Apply a color to both bands (red/white)
    Group (do not join) all, you cannot join different colored surfaces/polysurfaces and have them stay different colors.



CandyCane.3dm(2.3 MB)

thank you so much for your explanation!!! it wasn’t simple for me, but I get it, at the end.!!!
I agree, the uv map is the best way, to do that, but I want to try with geometry, mostly because after I convert parts in Zbrush, in editable mesh, and can rework them…