Hi,

I'm trying to model a flight around the inside of a cone, so that the width of the flight increases as it goes up.

So far I have swept a surface around a helix, starting from a 20mm line at the bottom:

I'd like the sweep to be 30mm at the top, increasing gradually until I get there, so this falls short obviously.

My guess is this isn't possible with a sweep, so I tried to loft it instead, using the helix as a guide:

This sort of works, but the profile twists outside the cone in an unexpected way as it goes up, which is no good. I thought I'd be able to drag the cyan dots to fiddle with it and maybe pull it into position, but it won't let me do that.

Next, I tried creating another helix on the inside of the flight (effectively between the cyan dots above) to act as another guide, using a variable helix based on the position of the point:

But this failed because this inner helix "does not intersect" with the end of the upper line, even though it looks like it does.

Is there another method for this? Ultimately I need to thicken, then flatten the flight to make it out of sheet metal.

Many thanks,

Tom