How to generate a screw based on wrapped curves and depth curves?

brad_phelan

Here is what I have so far.

https://cad.onshape.com/documents/63c77e740cd8b149ab1fa50d/w/2e6eedaf2b3ecc3b7480152d/e/df162b42ecb1048d0818c450



generated from a wrapped curve. Now I would like to raise make a ridge or lower, make a channel from the folder closed curve. Any idea how to do this?

To make this more interesting I would like the depth of the extrusion to vary along the z axis using a sketched curve.



and to make it even more interesting the extruded edged should look like a ramp not a cone. So a cross section of the screw
might look like


It's an interesting challenge. I have not been able to figure it out myself Be aware there is no guarantee that the width of the flights is constant. The wrapped curve can vary the width of the channel / flight. I would restrict it to say that it should be screw like in that the curves are monotonically increasing or decreasing in angle as they wrap around the cylinder.

If you want to see pictures of the kind of parts follow a google search here. http://bit.ly/2Dtwg7k. Here is an example of a typical screw.

konstantin_shiriazdanov

in some CAD's there are features like "varying section sweep" when you can set dimensions of the cross section to depend on distance along sweep path, or even to depend on the law given by sketch curves. but in this case you should be ready to write a custom FS, or at least do some job in surface style separately for each face of the "thread"

brad_phelan

I have some progress with manual operations that could be feature scripted and automated. 

https://cad.onshape.com/documents/63c77e740cd8b149ab1fa50d/w/2e6eedaf2b3ecc3b7480152d/e/df162b42ecb1048d0818c450

The curve of the flight was sketched in an unwrapped form then using "fold" from konstantin wrapped onto a cylinder. Unfortunately there is no emboss or scribe tool in OS yet so I had to do a sweep around the wrapped curve using another thirdpath featurescript "normal sweep" which is a bit buggy and then intersect that with a cylinder to generate a face which I then thickened to the correct offset.

Variable depth is not something I have a solution for yet.

konstantin_shiriazdanov

i would reccomend you to apply "Use path" checkbox and round corner of the helix line inside the sketch, so you get a smooth single edge helix

konstantin_shiriazdanov

some good enough starting point for variable depth helix cut, want to admit that surface sweeps and splits behave awfully, split fail almost every time and sweep does something strange with translation of original trajectory
https://cad.onshape.com/documents/aed55cfbfac2349650697209/w/a400c56074f1f4f9d5538f91/e/fbaed9534f99e3cf82731799

brad_phelan

I think if I will do it properly I will take the unwrapped channel curves, monotonic in angle ( when wrapped ) or Y axis when unwrapped and a depth curve as arguments to a single featurescript feature. Then I will generate all the intermediate profiles manually and loft them. It should be the easiest. I'll give it a go when I have some more time. Basically it is a matter of slicing the curves up at all the discontinuities and ensuring that there is a profile inserted at each point and enough in between to get the curvature tight. 

Thankyou for the effort