# Trouble with Revolve - Tutorial

**URL:** <https://discourse.shapr3d.com/t/trouble-with-revolve-tutorial/2531>\
**Category:** Modeling Questions\
**Created:** [June 15, 2018, 6:01am UTC](https://discourse.shapr3d.com/t/trouble-with-revolve-tutorial/2531 "2018-06-15T06:01:12Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![HoloWalk](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.shapr3d.com/holowalk/32/1253_2.png) [@HoloWalk](https://discourse.shapr3d.com/u/HoloWalk)\
**Post date:** [June 15, 2018, 6:01am UTC](https://discourse.shapr3d.com/t/trouble-with-revolve-tutorial/2531/1 "2018-06-15T06:01:12Z")

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OK, first of all, I feel stupid posting a question like this on a forum, but it would appear Shapr3D doesn’t have a tech support email address anymore and is funneling everything through this user forum. So forgive me in advance…

Trying to create a helix following exactly the steps in the tutorial,

- draw the circle
- draw the line
- select the revolve tool
- select the face of the circle, click next
- try to select the line as the edge around which the circle should revolve. But try as I might, I can’t seem to select the line… the app says its an invalid selection…

What would a “valid” selection be when I only have two things on the screen – the ircle and the line?

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**Author:** ![Zoli](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.shapr3d.com/zoli/32/592_2.png) [@Zoli](https://discourse.shapr3d.com/u/Zoli)\
**Post date:** [June 15, 2018, 7:57am UTC](https://discourse.shapr3d.com/t/trouble-with-revolve-tutorial/2531/2 "2018-06-15T07:57:23Z")

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Hi,  
I think the line you are selecting is not a straight line, revolve only works with straight lines or axes. If it seems straight, there’s a chance that it has not been drawn as a straight line. It can be an arc with a huge radius or a straight spline. You can easily check this. Tap with Pencil on the line itself, if a length dimension appears it’s a line and “Revolve” should work. But please also try to draw a new line and check if it is working with it or not.

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<div class="post-metadata">

**Author:** ![HoloWalk](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.shapr3d.com/holowalk/32/1253_2.png) [@HoloWalk](https://discourse.shapr3d.com/u/HoloWalk)\
**Post date:** [June 15, 2018, 2:19pm UTC](https://discourse.shapr3d.com/t/trouble-with-revolve-tutorial/2531/3 "2018-06-15T14:19:59Z")

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Thanks for the quick reply.  
I checked the drawing and it certainly looked straight. And snap to grid was on…  
Here’s a link to a screen shot.  
[![](https://us1.discourse-cdn.com/flex002/uploads/shapr3d/original/2X/9/9ac10e8ac6e2ded7e8e27394a7c792e65f923ae4.jpg) ](https://dl.dropboxusercontent.com/s/b6v1v3ga637303m/Revolve.jpeg?dl=0)  
(that oval at the top previously said “Invalid Selection” before I tried to capture the screen)

But I drew another line and it ended up being straight, I guess, because it would revolve around that line.

How can one tell for sure if a line is straight?