loft trouble

[DoWork]

First I tried lofting a simple shape: I drew two rectangles of different sizes (one slightly off center of the other), each with rounded corners. I converted to NURBS. Moved the smaller of the two rectangles +3" in Z (using the 3D Move command). Then "loft with no rail". Worked great.

Next I try the same thing only added some detail to one side of the smaller rectangle (IE: now the upper and lower rectangles do not exactly match). The details are some partial arcs protruding out and coming into the rectangle. At first when I attempt to "loft with no rail" I either got a warning "this loft can not be done" or when it does loft, the whole thing is twisted. I found out how to somewhat control the twist. In the Loft Creation box I got the arrows on each rectangle pointing the same direction (using the reverse button) and adjusted the Alignment by Percentage until it looked as straight as possible. But then when I previewed it, that particular part where the bright red line was (indicating the angle or twist) was the only part perfectly straight. Everything else had a slight twist away from it. Is there anyway to get no twist what so ever?

Could this all be due to the fact that my rectangle at the ground plane (Z=0) does not have the same details as the one that is above it(Z=+3)?

If that was too confusing please let me know and I can try to clarify or post files.

thanks,

DW

[Benson Shaw]

Lofts are great for some things, solid addition/subtraction works better for other things. Try making the protruding arc components (truncated cones? tilted cylinders?) as separate solids then add or subtract them to/from your first loft shape.

-B

[DoWork]

B,

That was my back up plan, but since I already had the two surfaces drawn with the protrusions I was hoping to get the loft working correctly. I guess at this point I have spent more time trying to get the loft to work than it would have taken to go the add/subtract solids route. I'm still interested in figuring out how to get the loft to work how I want it, if it's even possible.

thanks,

DW

[islandmon]

When Lofting make sure that both profiles have the same number of vertices.

But when one or more of the vertices is offset from one of the profiles... breaking the common plane... the Loft will skew from the desired solid. This is the case with protrusion & projections. It seems that the Loft is seeking the path of least resistance

in order to resolve the surface regardless of the shape of the profile.

Lofting is a really great procedure but restricted as to the shapes it can produce.

[DoWork]

islandmon,

There are no sharp corners, all corners have fillets. So I guess technically there aren't any vertices (is this correct?). Unless the ends of the fillets are also considered vertices, in which case there are different numbers of vertices between the two profiles as you mentioned. When you say "breaking the common plane", you mean the plane that connects two sides of the profiles that I am attempting to loft, right? This would describe the "more complex side" with arcs that I was referring to.

I tried lofting with just fillets in the corners (same # of vertices, no offset vertices) and no other arcs and got a similar result (twisting). Again I understand how to have general control over the twist, but not how to accurately control it.

thanks,

DW

[islandmon]

There are no sharp corners, all corners have fillets. So I guess technically there aren't any vertices (is this correct?).

Convert to mesh will show how that profile surface is derived mathematically .. and those polygons eventually will determine the sufficiency of the Loft.

If all the polygonal vertices match up .. bingo ... the Loft connects them into a surface.