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I have attempting to make a fin tube for two days and it is killing me.

Fin tubes are pipes that have a tight spiral of flat fins sticking out all around them. The spiral wraps around the circumference of the pipe. They are used in heat reclaimers among other places.

I made a spiral using the extra shapes add-on and scales pretty tight. And then I set the scale.

I made the fin shape and set its scale. I added the curve modifier and it jumped around a bit. I set its origin point to one end face and finally got it going the right way off the beginning of the curve.

Then I added the array modifier and moved it to the top of the stack. It all looked good for the first loop, then the fins started to tip. The outside edge aimed upward steadily as the inside edge seemed to continue to be oriented at the center base of the curve.

How can I keep the darned things at 90 degrees to the z axis? Or should I be using a particle system? I haven't learned that one yet, sigh.

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    $\begingroup$ Could you please edit your question and provide some images of your problem? Perhaps a few reference images of what you want to achieve and screenshots of your model, including the modifier stack and relevant settings $\endgroup$ – Duarte Farrajota Ramos Jan 20 '17 at 1:46
  • $\begingroup$ Also if I imagine correctly what your are experiencing is probably a twisting effect cause by the curve tilt. Try changing the curve tilt to something like Z-Up and see if it improves. $\endgroup$ – Duarte Farrajota Ramos Jan 20 '17 at 1:48
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If I understand correctly the deformation you are getting is cause by the spiral curve being naturally twisted itself.

You can probably minimize this by changing the curve tilt per vertex (which would be very cumbersome), or overriding it's twist mode.

In the Properties Window > Object Data (Curve) > Shape > Twisting switch it from whatever you have now to Z-Up and should ease the problem

Fin Tube Curve Twisting

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  • $\begingroup$ Hi Duarte, thank you! That looks like exactly what I was looking for. I'm sorry I didn't add pics. I had left the studio and was mulling it over on the ride home when I decided I need to ask for help. I will take a closer look at the properties window and give it a try. $\endgroup$ – Matt McKee Jan 20 '17 at 2:16
  • $\begingroup$ Your little demo sure looks like a fin tube! I have so much to learn! $\endgroup$ – Matt McKee Jan 20 '17 at 2:17
  • $\begingroup$ Duarte, You were exactly right on the money. It was in the Properties Window > Object Data (Curve) > Shape > Twisting Z-up setting. I still need to work on this more and try a render at a higher sample rate to get rid of fire flies. But, this is what you helped me to make. Thank you! Fin Tubes $\endgroup$ – Matt McKee Jan 20 '17 at 21:27
  • $\begingroup$ Ah, got it, guys. Thank you for the correction. I wanted to add the photo but don't see the upload image button or even the format bar. I know this is off topic but how do you add an image to a comment? Or is that not acceptable protocol? Ah, never mind. I think I need to reread the help center posts! $\endgroup$ – Matt McKee Jan 21 '17 at 13:32

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