Variable Pitch Thread/Helix

[Anonymous]

Hi, 

I would like to create the helix as shown below, with variable pitch throughout its set height. In the end, I would like to say the helix's pitch reduces by 35% over its height. 

Is there a function inside Fusion360 for this? If it helps at all I am from a SolidWorks background. 

Thank you in advance,  

Tom

[etfrench]

One of these two threads should have your answer.

[sanket223.patil]

There should be a easier way to do it , Fusion should have This Function .

[andreasbovin]

I found that none of the two threads really fixing my problem. They suggest making separate helices which are then spliced together, but this is not a continuously variable pitch helix. 

I found a workflow that creates this, however! It's pretty tedious and difficult to control with respect to end dimensions and parameters, but it is possible with some fiddling around.

Step 1: Make a spiral tube on the bottom horizontal plane. Include the outer edge 3D geometry of the tube in a separate sketch for later use.

Step 2: On a vertical plane sketch a profile for revolving around the center axis of the spiral. Make a spline or parabola shape or something else that has an varying slope. This is the effect we'll use to gain varying pitch in the end result. Surface revolve the shape.

Step 3: Surface extrude the spiral up to the revolved shape, using the "To Object" end criterion. 

Step 4: Surface extrude a cylindrical shape from the bottom plane. 

Step 5: Project (closest point) the intersection curve onto the cylinder, or split the cylinder face using an surface Extension from the intersection curve. The resulting curve on the cylinder will be a helix with variable pitch. 

See the screencast for details, even though the demo model is not very impressive. And let me know if it is usable to anyone! 

[andreasbovin]

Here is the screencast

[MichaelT_123]

Hi Mr.AndreasBovin,

Ohhh..., I have watched it all until the victorious end.

It looked like you hard break into a banana ... from the wrong end.😉 

Consider a different approach - one with more engineering flavour.

Here is a helix equation:

x(θ) = a*cos(θ)

y(θ) = a*sin(θ)

z(θ) = b(θ)*θ

Your 'variable helix' term is hidden under the factor-function b(θ) (for standard helix b(θ)=const)

Just devise a proper in your circumstances shape of it, gather equation's point, build a spline,....and you will have your spring designed in the precise, predictable way.

Much more, as the spring will be described analytically, you will be able (with some pinch of luck) develop a mathematical model of the spring's mechanical characteristic also.

Regards

MichaelT

[andreasbovin]

Yeah, it felt like opening the banana from the wrong end, too... 

I know about the helical equation, and that you can build splines from points, but I wanted to avoid that since my experience with Fusion 360 add-in stability is not great. And I agree that my method is absolutely not optimal. Nor controllable. 

Do you have suggestions for a good add-in for making equation drives splines in Fusion? By the way I'm not trying to make a spring.

[MichaelT_123]

Hi Mr.AndreasBovin,

... writing the respective script to generate what you want would be quite easy.

Go to API section of the forum and type 'helix' in the search box. You will find some examples there.

Regards

MichaelT