a way to make an exponential curving helix

eelco_roes

Hello,

I am trying to creat a cam cut in a spherical surface. It works fine using the helix tool and sweep the shape. However I need the curve to have an variable angle where it increases exponential. I found a workaround to create a sketch with the curve as I want it and wrap that over the surface and cut it out. than use that cut line for my sweep. However that deforms the shape I cut for some reason I don't understand. How can I creat a regular line that I can add to the surface as the helix as a curve and use that?

With a regular helix shape

With the drawing wrap and cut and sweep.

Deformed

MichaelPascoe

There are a few different ways I can think of to dynamically change the angle of a helix profile. One way would be to create a variable pattern where you use an equation to adjust the profile as it patterns along the helix. Then you could use Loft to follow the path and use the profiles as your inputs.

Is there a picture of a finished product that uses this technique? I'm having trouble picturing your final result.

eric_pesty

The parametric curve FS might be helpful for that (provided you can figure out the correct equation for what you are trying to do)…
https://cad.onshape.com/documents/578ff8b3e4b0e65410fcfda3/v/69f7db3196182c708f8e4835/e/0c17de6a800d4aed83de417f

eelco_roes

https://forum.onshape.com/discussion/comment/109777#Comment_109777

Thank you I will try it out

eelco_roes

The final product is a lens focusing system. where originally lenses uses an multi start thread. modern lenses uses a cam system like the one I try to make here. when a lens focus from infinity to close focus the focus slows down where you have to rotate very little to go from say 10 meters to infinity but use say 25% of the rotation just from 10cm to 1 meter. So the cam curve compensates that to speed up focus when you go from infinity to close focus. I hope that makes sense.

Here another example of a first attempt, the white block is pushed inside that track (purple part) spring pushes it up. purple part rotates and pushes the lens (yellow part) forward/backwards.

MichaelPascoe

It is still hard to tell what you are actually trying to do.
Please share a link to your model with edit access. Or a link to a copy of a portion of your model if you are worried about people copying your work.

It will help if you share a real life example or model of this helix or thread in it's finished state so that we can see what you are trying to do.