# Construction lines on a curved surface

**URL:** <https://discourse.shapr3d.com/t/construction-lines-on-a-curved-surface/26991>\
**Category:** Modeling Questions\
**Created:** [July 26, 2023, 9:11pm UTC](https://discourse.shapr3d.com/t/construction-lines-on-a-curved-surface/26991 "2023-07-26T21:11:18Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![jmstovall](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.shapr3d.com/jmstovall/32/21395_2.png) [@jmstovall](https://discourse.shapr3d.com/u/jmstovall)\
**Post date:** [July 26, 2023, 9:11pm UTC](https://discourse.shapr3d.com/t/construction-lines-on-a-curved-surface/26991/1 "2023-07-26T21:11:18Z")

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Got another one that I think is straightfoward, I’m just lacking knowledge.

I’d like to place an object dead center on the “bottom” of this object:

 ![Screenshot by Dropbox Capture](https://us1.discourse-cdn.com/flex002/uploads/shapr3d/original/3X/b/e/bed6ca40f8bde895f43970d61533c28e4d68aab5.jpeg)

But I can’t get a sketch to “stick;” it’s not allowing me to put a plane on a curved surface so that I can draw construction lines to guide me.

For context, the goal is to put a simple block on the bottom of the cylinder that aligns to a cutout on a base (not shown) to make a traincar for my kid.

Thanks in advance!

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**Author:** ![Lout](https://avatars.discourse-cdn.com/v4/letter/l/a6a055/32.png) [@Lout](https://discourse.shapr3d.com/u/Lout)\
**Post date:** [July 27, 2023, 2:11am UTC](https://discourse.shapr3d.com/t/construction-lines-on-a-curved-surface/26991/2 "2023-07-27T02:11:28Z")

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One way would be to add a construction plane to the end of your cylinder, rotate 90° and then lower to the base of the cylinder

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<div class="post-metadata">

**Author:** ![jmstovall](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.shapr3d.com/jmstovall/32/21395_2.png) [@jmstovall](https://discourse.shapr3d.com/u/jmstovall)\
**Post date:** [July 28, 2023, 5:22am UTC](https://discourse.shapr3d.com/t/construction-lines-on-a-curved-surface/26991/3 "2023-07-28T05:22:41Z")

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Yup, that’s what I went with. Thanks for the trick!