Lofting issue / bug / I'm not doing this right?

[teardrop3d]

I'm having issues with lofting straight line profiles along a single complex rail.

The final surface has the cross-section curved and kinked - even though the 1st and last cross section are straight lines. What am I doing wrong?

I've tried

• adding more cross-sections the surface likes to turn into complex curves on either side of the profile
• trying to do 1/4 of the rail with GO, G1 & G2 (with some horrible twisting with G2)
• tried doing 1/2 of the rail with same results.

However if I take the same surface to Rhino I'm able to generate the surface with no kinks using a 1-rail sweep command. Actually I was able to generate the 2 surfaces in one step allowing the hard edge to blend into a single edge at the tip.

Is it a limitation, me or bug?

Thanks in advance 

[g-andresen]

Hi,

please share your design to take a look.

günther

[teardrop3d]

Here we go!

https://a360.co/3gTqmQ2

I've created a closed loft in the above example which accentuates the kinking.

Thanks in advance

[davebYYPCU]

What am I doing wrong?

Expecting more from Fusion than you are defining. (You need 3 rails)

Fusion has an inbuilt shrink wrapping ability for compound curved lofts, the best example is your quarter Loft, if you deselect the rail, the algorithm works correctly, add your rail and there is not enough definition for the program to know what you want, so it tends to introduce the wave, where a lower rail and centre rail would remove the curling.

Edit; After a second look at this, change your rail to be a centre line rail, fixes it.

Might help....

[teardrop3d]

I tried a lower rail but still gets waves.
A center rail.... That's close to impossible to create using fusion360
tools! But I'll give it a try...Thanks (the problem is that it's so easy to
create in other programs! - but I loose the ability to easily modify the
design later)

[davebYYPCU]

Not sure you saw my edit - update, 

Might help....

[teardrop3d]

Thanks! Center-rail seems to solve the issue for one of the surface (although I end up needing to do a closed loft) but doesn't work for the other loft surface. I think the loft can't resolve the disparity in lengths while maintaining the rail