Creating a loft from a body to sketches

[Anonymous]

Hello, I'm fairly new to fusion 360 and having a little trouble with creating the shape I need. I am trying to create a loft between the bottom of my fan blade and the circle that that is going to be the base of the blade once done. I can get loft created, but the surface keeps the edges of blade profile. Is there a way to get this to not continue past the first profile of the loft so the end result will be smooth?  

[TrippyLighting]

I am not at my Fusion station at the moment but I beieve there are at least two ways to do this:

1. Instaed of making the loft between a solid 3D body and a 2D circle you can try to create a 3D structure with the circle before lofting between the two solid bodies. This may help maintain tangency between the surfaces and result in smooth transitions.

2. Use a loft with rails. The rails will help you to control the "flow" of the surface and precisely define tangency and curvature but lofts with rails can be bit of a challenge.

[Simon.Hern]

Hi @Anonymous.

I may be misunderstanding what you're trying to do, but I'm assuming that you want to loft between the base of the blade and the circular sketch, like in the picture below, and you want that loft to join smoothly with the blade.

This should be possible by simply selecting 'Profile 1' to be 'Tangent' in the loft dialogue - but as the picture shows, that doesn't appear to have the desired effect.

I'd thought there might be a bug in how 'Tangent' works, but looking more closely at the model it turns out that 'Tangent' is in fact working correctly.  The problem is that 'Profile 1' is actually part of a very, very thin cylinder - you have to zoom in a lot to see it - and that is what the loft is connecting smoothly to.  If the blade is built without that cylindrical part then the loft should connect smoothly.

But as I've said I may have misunderstood what you're trying to do.  @TrippyLighting's tips for controlling loft shapes are good ones.

Simon

[Anonymous]

Yeah I think my other sketch confused you a little. The one you have selected as profile one is where my loft will end. The othere sketch is for a different part. As you can still see towards the blade the edges are still coming down into the circle part of the loft. I have tried to change to profile 1 to smooth and tangent and the results are worse. I tried to change the last profile to tangent and all other loft options, to no solution. I have tried creating rails to guide the outside profile, but having difficulties getting it to intersect all profiles. If there is anything else I'm missing or any other way to do this I'm open to all suggestions. 

[Anonymous]

Thanks for replying.  I tried deleting that thin cylinder and just have a circle sketch and tried creating a cylinder to loft to as well. This did not change the smoothness. It still has the blade edges coming down into the cylinder part. I tried to sketch two rails to guide the profile but having trouble getting it to recognize the sketche intersects all profiles. There must be a step or something I am missing to properly create this loft, Or maybe the shape will not allow it to be smooth, wich will not work. 

[Simon.Hern]

Hi @Anonymous.  Sorry, I had completely misunderstood what you were doing.

If I'm understanding you this time, you want the loft that's already in the model to have a better shape.  In particular you want to get rid of the 'creases' in the loft surface, as marked in the picture below.  (Incidentally, while it looks smooth at one end, the blade profile actually has four 'corners' rather than two.  Fusion is quite fussy when it comes to smoothness.)

Unfortunately I think it's always the case that a loft surface will have a crease where it touches a non-smooth profile.  One way of getting around this might be to fillet the edges of the blade so that it has a smooth profile, but I had trouble getting this to work when I tried it.

A better approach might be to build the shape you want from two separate lofts.  If you sketch a new profile that's similar to the blade profile, but perfectly smooth, then one loft surface could be between that and the blade, and the other between that and the cylinder.  The second surface would be smooth even though the first one wouldn't.  By selecting a 'Tangent' boundary condition, the two loft surfaces could be made to join together smoothly (this would work best by building the smooth loft first, and then joining the non-smooth loft to that).

That said, when I tried that approach quickly just now I couldn't get it to work - the loft operation really seems to struggle to deal with that blade profile.  I'll post something if I can get it working.

I'm a bit of a beginner when it comes to Fusion I'm afraid.  Hopefully other people can suggest better ways of approaching this.

Simon