2D line to 3D line loft

[Anonymous]

I am recreating a motorcycle seat and took some pretty good top and side pictures to give me something to trace.  I was able to trace the profiles, and created an intersection line without much difficulty.  However I am having some problems Patch-Lofting one of the 2D sketch lines to the 3D sketch lines. I can't get any farther than the picture below, it keeps adding the additional sections of the 3D sketch as another profile as opposed to adding it the Profile 2.  I attached the archive file too.  Thanks!

[Anonymous]

So I redid my sketches so that the two lines I am trying to create a plane between are one single line each.  However I'm still having an error message when trying to Patch - Loft the two lines.  I have messed around with the profile order and the continuity and eventually did get some sort plane inbetwwen them but I don't think it really is a true plane.  The thicken command isn't working and when I zoom in on the corners I can see theres some circle edge, which shouldn't be apparent on a infinitely thin surface.  I went ahead and put a picture of the error and the plane error if it helps.  Also attached the archive file.

[Anonymous]

Just realized you can't really see that first picture.

[jakefowler]

Hi @Anonymous,

I think the Loft issues are stemming from the fact that the two profiles don't meet precisely at a point. If you look at the model from the Top view, and zoom in close to one of the end points, you should see a small gap between the two profiles:

Ensuring these meet precisely is important to getting a high-quality resultant surface. The way to do this is:

1. When you draw the first curve, ensure that the end points lie exactly on the plane of the second curve.

2. Before you draw the second curve, use the Project tool to project the end points from the first curve into your second sketch. Then add Horizontal/Vertical constraints to make sure the end points of your second curve align with those from the first.

I'd also recommend using fewer points in your splines. It's tempting to match a shape by adding as many points as needed to closely match the shape, but having a lot of points in your curves will result in surfaces that have little bumps (sometimes barely perceptable - use the Zebra Analysis tool to better visualise this), and/or might cause more problems when you try to add features downstream. It's much better to add a few points as possible (generally I insert one point every time the curve changes direction) and use the tangent handles to adjust the curve shape so that it matches you reference image.

Lastly - since your surface effectively travels in a straight direction, you might actually be better off to Extrude this surface rather than Loft it. Extrude the side profile, then open the Trim tool and use the other spline to trim the extruded surface. This will result in an extremely smooth and clean surface (as a general rule, Extrude + Sweep give the cleanest results but can only be used in some circumstances, whereas Loft + Patch are more flexible but result in more complex surfaces).

The screencast below hopefully explains these issues and suggestions. I've attached the f3d I ended up with as well. Get in touch if you get stuck with any of this.

Thanks,

Jake