Problems with loft?

[Anonymous]

Hi Guys, I have been having a hard time getting Fusion loft to work the way I would like it to?  See pic, I am trying to create a teardrop-shaped loft with two profiles and three guide curves however I get a crease every time I mirror my newly created one half of the teardrop shape shown in blue. Profiles and guide curves are made up from splines is this causing my issue?  Should I be creating it a better way? I am setting the spline handles to horizontal at the top of the guide curves in an effort to have a smooth center line over the top of the shape. 

Thanks for the help!

Werner

[ryan.bales]

It's tough to say without getting to mess with it. Can you upload a file? I'm not sure what outcome you are trying to achieve so i'm not positive what crease you are talking about. 

[Anonymous]

Thanks for the reply Ryan!  The Crease is apparent most at the ends (see pic).  I am wanting to achieve a smooth top of the teardrop shape. I am thinking it is a problem when using splines?  One other thing I have noticed is that the spline handles are buggy when trying to set the handle horizontal and then create a coincident constraint to the end of the spline and a profile. This operation seems to lock up the spline handle but not horizontal. The coincident constraint to profile shifts the handle to what looks like a random angle and can no longer be manipulated. 

[TrippyLighting]

@ryan.bales no, that's actually fairly easy to explain.

The loft rails, or profiles are all set to "connected". I believe when the rails/profilaes are sketch objects "connected" and "direction are the only options.

So the first thing the OP can try is to set the option for the central rail to direction.

A better workflow would actually be to extrude a helper surface from that center profile/rail and use the edge of that extruded shape as one of the profiles. Then the loft options allow to define tangency(G1) and continuity(G2) and associated weights. When the loft then is mirrored there will be no crease.

@Anonymous if you can post the design (export as .f3d and attach) I can demonstrate this in a screencast.

Edit: In general I predict this loft will have crappy curvature on the edges where it connects to the main body. The reason for that is the base profile for the loft is offset from a projected profile. That combination has the tendency to kill smooth curvature.  

[ryan.bales]

Dare i use a pun and say you have 'loftier' Fusion lofting knowledge?  I agree with you, although without seeing the loft dialog box I tend to err on the side of caution. But as usual, i'm glad you chimed in.

I really like this suggestion!

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@TrippyLighting wrote:

So the first thing the OP can try is to set the option for the central rail to direction.

A better workflow would actually be to extrude a helper surface from that center profile/rail and use the edge of that extruded shape as one of the profiles. Then the loft options allow to define tangency(G1) and continuity(G2) and associated weights. When the loft then is mirrored there will be no crease.

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[Anonymous]

Thanks so much for the ideas Guys!!  You have given me some ideas to play with!  There does seem to be some magic in creating an extended first to select the profile from!  I am still not fully understanding the direction option? For example, the takeoff weight and takeoff angle don't seem to do anything?  I do have the file I am playing with attached!  Thanks again, have a great day!

Werner

[TrippyLighting · Accepted solution]

Ooookay.......

So There are a number of things that need to be considered when trying to loft a shape such as this.

1. In order to get good curvature across the shape the profiles in sketch 1 and sketch 2 should have the same number of control points to control the spline. The shape of the spline can be changes with the spline handles.

2. The rail you created will control the curvature of the loft. That is one of the reasons the weight settings don't do anything. However, that rail is not tangent or curvature continuous to anything.

So here is how I would loft this. Sometimes lofting in the model environment works beautifully, but sometimes it works better in the patch environment. In general, however, when lofting in the patch environment one has more control over the surface.

[Anonymous]

Peter, I can't thank you enough!!  You made it crystal clear in the video, I watched it a few times!  Patch is a powerful tool I just need to go to it more often.

Thanks again Buddy, have a great weekend!

Werner