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# How to draw a helix with varying pitch

Hi

I need to draw an item that has a helix that varies in pitch as it goes around a cylinder. as per attached picture.

I started to try and do it by adding multiple surfaces going up a cylinder and adding a different helix on each surface. but it didn't really work.

It would be good to be able to use spline tool around the cylinder. but you can't sketch on the surface.

So how would you do it?

I need to draw an item that has a helix that varies in pitch as it goes around a cylinder. as per attached picture.

I started to try and do it by adding multiple surfaces going up a cylinder and adding a different helix on each surface. but it didn't really work.

It would be good to be able to use spline tool around the cylinder. but you can't sketch on the surface.

So how would you do it?

0

## Answers

1,005✭✭✭✭✭x=r*cos(t),y=r*sin(t),z=k*t^2, r - radius of helix, k ~0.1 - some free factor1,381If this was a feature, what would the input parameters be?

Philip . . .

1,005✭✭✭✭1,381If i want a constant rate of change of gradient, the projection of any curve that exhibits that behaviour would become very skewed (rapidly decreasing gradient as you move away from normal to the surface). Is there a trick that i am missing?

1,005✭✭✭✭Or, just do as konstantin suggested and use my parametric FS to generate the 3D curve

33✭✭✭Then extruded a polygon with 50sides.

Plotted points along the polygon following the imported images.

Used the 3D spline feature script and selected all the created points to create a curve that matched the part.

I then tried to sweep along the 3d spline but the sweep doesn't stay tangent to the polygon and ends up turning into it.

Using helix sweeps stay tangent to the part but don't suit in this case.

1,005✭✭✭✭https://cad.onshape.com/documents/57acdfaae4b005c413ed9b6f/w/3fd585a46d3af1b3ba413c53/e/052b9b1376888b5d8b16e4f1

1,381https://appstore.onshape.com/apps/Utilities/KQ5H3ZDPXICD2PJKVGR6RJZ3HFNAJ2IQQMBBZFQ=/description

1,005✭✭✭✭1,3811,005✭✭✭✭✭about swift calc and related engeneering calculations, did you heard about wolfram cloud invironment/wolfram language? they developed a very powerful symbolic calculations environment, would be nice if OnShape had an integrated tab with wolfram notebook, and even some featurescript functions might be implemented in Wl