How to set Loft Direction?

[Anonymous]

I'm trying to create two lofts that are mirrors of each other (yes, I know I can use the mirror command), but there seems to be a set direction the loft flows, so the second one ends up not looking anything like the first.

Here's my starting Sketch. I want two lofts - one from each pair of circles down to the rectangles:

So I create the loft on the right

Then create the loft on the left

You can see I use the exact same parameters, but they look VERY different. 

Only when using the Mirror feature, can I get what I want:

So, is there a setting somewhere that I'm missing to set the Loft Direction? (I think that's the issue here), or is this something else entirely? Or am I stuck with using the Mirror feature to get lofts to do what I want?
Thanks!!!

[davebYYPCU]

It is more to do with the Mapping handles, the big white dots on the perimeters of the profiles while the tool is in preview, they are movable to guide the shape.  Click and drag a white dot, but you can't allow them to cross over each other, 

You can sorta see why they are different, as the tool is placing those handles differently, and certainly not symmetrically

or you can make your own guide rails, to help the tool work the way you want it.

Might help.....

[Anonymous]

Interesting, but that doesn't seem to be the case - or its a bug.

Here's the right side dot positions:

And here's the result after clicking 'Done'. It like totally ignores the circle positions:

Then, here's the Left Side Dot Positions:

And the result after click on Done. It appears to follow the dot positions there, but not with the right side loft:

Am I just not getting what you're saying??

Thanks!!

[TrippyLighting]

No, that's not a bug. You need to step back for a moment and think about what you are actually asking the tool to do.

You need to think of this object as separate surfaces, because any CAD software has to build this shape from NURBS surfaces.

The rectangle you use as one profile has 4 sharp corners and 4 lines. If extruded straight it would result in 4 planar surfaces..

The 2 overlapping circles  have 2 sharp corners where the circles intersect and would result in two cylindrical segment surfaces if extruded straight.

Now the software has to figure out how to map 4 edges on one profile to 2 edges on the other and makes assumptions. In order to help it you get these 4 twist control circles on the double-circle profile that you need to adjust so the software can actually map these edges the way you want it.

Chances are, however, that both lofts still are not going to be perfectly symmetrical, because we don't have any precise numerical controls for these test control handles.

[Anonymous]

Yup, I'm not getting it.

On the left side, it puts lines where I have dots, but on the right it does Not:

[davebYYPCU]

So click and drag a white dot, you will get a temporary red line showing its respective other end.

The Loft Tool is making its educated guess on how to do the transitions, but you have a limited range to guide it with these handles.  I don't think you can add mapping handles, and I don't think you can delete any either.  Unless you attempt to manipulate those handles, you gets what you are given.

So you can add your own Rails, that the tool has to take into account.

So far there are 5 handles in each loft, I would be making 6 rails three each side and symmetrically paired up.

Did you attach the file - we can demonstrate with your data way easier than on a typewriter.

[Anonymous]

First off, I really want to say "Thank You!" for trying to help me and my old brain understand this thing I'm having issues with. Thank you!
Attached is the F3D file. I've suppressed the last 2 features, as they are the Mirror across a plan to make the lofts match.
And as I said before, I can grab and move the dots, and the lines show up where they are connected, but when I click 'Done', those lines magically move like it didn't pay any attention to where the dots where - but only on the right loft (Loft1).
Again, thank you all so much for your help!

[Anonymous]

Here's another example:
I have I dot set and the line shows where it will go. This is the default the Loft feature gave me. But when I click on OK, the line takes a totally different path than what the Edit showed:

[davebYYPCU · Accepted solution]

Pure guesswork on what you would like for the actual shape, 

solid loft did not look like being close with just 5 handles, that I was able to adjust, 

sketched 6,  3d rails with 2 point splines, and

adjusted for close to tangent (actual tangency fails as well) to the rectangle, and

normal to the figure eight. 

Solid loft was self intersecting, so did it with 6 patch lofts, capped the lofts and stitched to solid. 

File attached, you can tweak the spline handles now for your outcome, 

Might help

[Anonymous]

Thank you for all your help. I have a better understanding of how to control lofts now so that hopefully I can create two or more that are nearly the same inside a model.
But I still don't understand why when it shows a white circle and line in a specific position during edit, that it often moves that circle and line when I click OK. Seems like a bug.

But at any rate, thanks again for your help.