Making a sketch line on cylindrical surface, parallel to axis of cylinder

[tom.vihvelin]

The simple task of drawing a sketch line on cylindrical body surface, parallel to axis of cylinder but always tangent to the cylinder had me stumped. Granted I am a Fusion Newbie, but been doing CAD for years.  I was finally able to accomplish this with a method that I did not think would work, but it did. If someone has a better method, please, please let me know!

Here is how I made it work. On a simple cylinder, I started a new sketch using the flat end of the cylinder as my sketch plane.  To draw the tangent line, I selected a point on the periphery of the flat end of the cylinder. Then I went to the opposite flat end of the cylinder and selected a corresponding point on its periphery. I was shocked to see Fusion create the line.

I though you were only allowed to sketch on the sketch plane and nowhere else but this line is not on the sketch plane. What gives?  Is there a better way?  Thanks for all input.

[jeff_strater · Accepted solution]

Nothing wrong with that method.  Sketches in Fusion (unlike other CAD tools) are inherently 3D.  You just created a "3D line" in that sketch by snapping to those points on the cylinder.  There are plusses and minuses with 3D geometry.  Not all of the functions from 2D geometry are available for 3D lines/curves (offset, fillet, some constraints, etc).

The other way would have been to create a tangent work plane on the cylinder, where you want that line to go.  Then, sketch on that plane, Project in the edges from both ends of the cylinder (this results in a line).  Draw your line from the midpoint of one to the midpoint of the other.

[tom.vihvelin]

Thanks for that super-quick response Jeff and for doing that demo of an alternate solution.

[jordy_keller]

Nice challenge, I had a go at it too.

Sorry no screencast but screenshots

Create a random cylinder with a 3D sketch:

Construct a tangent plane on the cylinder surface

Start a sketch on the new plane and use project/include > intersect on the cylinder 

Use edit feature to adjust the angle