# How to Coil around a Cylinder

I’m at a loss to know how to proceed and would appreciate some guidance.

I have a cylinder that is 11" high and 6-5/16" in diameter as shown in the attached file. I want to model this cylinder being wrapped by a continuous coil of 3/8" diameter rope, or in this case insulated electric wire. If I knew how to draw a coil of a single line, I’d put a 3/8" diameter circle on the end, select the coil line then click the Follow-me Tool. My problem is that I’m drawing a blank on how to draw a coil. Because I want the coiled electric wire to appear touching the coils above and below it, I’d also need to know how to account for the pitch of the coil to wind up the cylinder in that fashion.

If someone could point me to a wiki or tutorial, I’ll give it try and come back if I still have questions.

TIA

Cylinder.skp (156.5 KB)

I’d use the Helix tool in the Curve Maker extension to create a helical centerline path and use a 3/16 in. radius circle for the profile and use Follow Me. Adjust the height per turn on the helix to adjust how close you want the turnes.

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Another option would be Trubend, use the circumference for the length of the tube to bend, then array it.

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I’ve just looked at your model @rabbithutch and you are hiding things with materials, Make sure you work with faces correctly orientated, mostly your cylinder is inside out with one section the right way.

But this is what I meant with truebend,

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I didn’t even look for reversed faces. Shame on me.

@Box is correct about the face orientation.

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I guess I don’t understand what you mean, Box, about hiding things with materials. As for work faces being correctly oriented, I don’t see what you mean. Did I fail to reverse faces before applying the color to surfaces?

I DID get the Curve Maker extension. I’ll have to learn how to manipulate the helix tool. So far I haven’t looked into TrueBend. I’ll save that for tomorrow. It’s getting pretty late for this old tired brain. I’m going to get a night’s sleep and see if a fresher set of eyes will help.

Thanks to you both, Box and Dave. Until tomorrow . . .

Yes, I think you got the idea of Box’s comment. Usually you want to keep the front face (white in this style) outward and the back faces (blue) as the inside of shapes. When you apply materials too soon in the modeling it’s hard to keep track of face orientation. Just view the model in monochrome and that will help you see where to orient faces.

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Box, I don’t understand how you made the original 3/8" cylinder lift at the end by 3/8". I calculated the length needed to wrap the 6-5/16" circumference to be 19.84" and made my cylinder that length.I tried using the Move Tool like you did in the video but could not by selecting the opposite end from the end the Move Tool is used on. It wouldn’t work as it did in your video. I’m not running Pro; so maybe the tool works differently in Make. I also experimented with Truebend and discovered that the bending face must be aligned with the red axis and that the object to be bent must be a group.

What else do I need to know?

UPDATE: OK, I figured out how to get the cylinder lifted. I did it by drawing a line the proper length then raising a perpendicular by 3/8" and connecting the top i\of the perpendicular to the opposite end of the line then deleting the original line and the perpendicular line. I then placed a 3/8" diameter circle on the raised end of the line and used the Follow Me Tool to have it encompass the length of the line. I was then able to use the TrueBend Tool to make the first coil. I was careful then to reverse faces on the resulting cylinder.

This brings me to my next questions. What did the Outer Shell command do and why did you use it? Also, softening the selected coil does not remove the lines at points of connection. Can I fix that?
Cylinder.skp (4.8 MB)

Outer Shell combines two or more solid objects into one. @Box used it to join his single turns into a one group. Not required with my method.

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Thanks, Dave!

I’m still working with the helix command. Haven’t figured it out yet.

First, how did you turn the single line helix into a tube? Second, how did you get the coils to touch each other. Third, how did you get the uncoiled ends.

If you start the tool from the toolbar…

And you can change your mind on each of the settings if you need to.

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You are GOOD !!!

I used the Up arrow key to lock it the blue axis, alt would also work.

You can select the outer top ring of your cylinder and read the length of that, which is the circumference, in Entity Info.

Yes, that is part of using a new tool, you need to learn how to use it.

The method you used here means the rings you create aren’t solid, so the outer shell does nothing and softening will not remove the edges.

Dave has given you a good method, no need to use my clunky option.

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Thanks, Box! I’ve been working through as best I can using Internet sources and experimenting as I go. I really appreciate your guidance while I’m learning the tool.

Dave, thanks for the tutorial!

I managed to get as far as the spiral in the attached file. I probably didn’t get the spacing right - I used 3/8" and might should have used 3/4" based on the spacing in the result.

2 more questions:

1. how do I make the single line into a coil or tube?
2. how can I add lengths of coil to the ends of the helix?
Cylinder.skp (4.9 MB)

For a tight wrap like in my first screen shot, the height per turn needs to be the same at the diameter of the circle used for the profile. If you want 3/8 in. diameter, make the spacing 3/8.

As I wrote and showed in my first reply, put a circle on the end of the helix and use Follow Me. The helix is formed as a group so you need to either edit the group to add the circle or explode the group.

I extended the ends in my second screen shot using Push/Pull. You could also draw additional geometry to lengthen the path before running Follow Me if you want. That’s basically what I did for these springs and the string on the pump drill.

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Something to be aware of, if the circles touch as they go around the spiral the result won’t form a solid. If you don’t need a solid that’s OK.
Even with a small gap, due to the way follow me twists, the rings will probably come together at some point which can cause solid inspector to say all is good but sketch not see it as a solid.
There are lots of peculiarities to this type of shape that can get confusing.

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Box makes a good point about having a solid at the end. Solids can be useful and are generally easier to work with so it’s a good idea to shoot for that.

I did this using 0.374 instead of 0.375 for the radius of the profile circle. SketchUp calls it solid with no problems and the gap is so small that you’d have to zoom in quite close to see it. Probably wouldn’t make a difference in most modeling.

Here’s a version where the coils ‘join’ making a solid with no gap.
I’ve used the polygon tool here to help show what is happening, it has the added benefit of being able to toggle the way the vertices are positioned. You can see as I’m creating the circle how the shape flicks from point to flat as I tap the ctrl key. This way the flat is at 3/8th. (circles and polygons are never a perfect circle, the size varies from vertex to mid segment) So when you use the outershell tool the flat face between the coils is removed.
This can be done with a circle, of any even number of segments, just by rotating the circle half a segment. Or use a polygon of any even number and weld the edges before you extrude. (the polygon tool really just creates a circle with unsoftened vertices)

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Dave, I tried using the Follow Me Tool. It worked in one instance (coil is colored and orange-red) and failed in the other, as you can see in the file… I’m sure I must have done something differently but don’t know what. As far as I can tell, the helix does not have the Group attribute . . .

After selecting the helix, clicking the circle with the Follow Me Tool produces and error saying, “This does not appear to be a valid path.”

A question about helix attributes: What does the Sides/Turn option mean or do?

Cylinder.skp (8.9 MB)