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2D guide lines on a loft
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May 02, 2015, 06:22:39 AM
Question for a TC Pro 18:

Anal as it may be my objective is to show a rubber band mounted and realistically twisted up between two round posts much like you’d have in a model airplane’s fuselage.  The issue is the transition segment between each end and the helix at the center. Admittedly I simplified the part not including the bothersome bulging exterior as shown on the helix.

The rule for a loft has the guide lines as shown in a 2D plane, but I think this actually needs a 3 D plane here, looking at the end view as the material (yellow) leaves the helix abruptly and doesn’t remotely comply - unless I’m not doing something right?

Thanks,

Bob   

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* May 02, 2015, 07:05:20 AM
#1
Bob, I just wondered if you had seen Henry and John's replies (and Henry's file) in you other thread.

http://forums.turbocad.com/index.php/topic,16476.msg96848.html#msg96848

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* May 02, 2015, 08:44:51 AM
#2
Hard to tell what's what in that drawing, since I can't find any profiles, paths, or guide lines.

Henry H

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* May 02, 2015, 11:25:06 AM
#3
Have you considered a Twisted Extrude, with G1 or G2 Continuity, for the twisted portion and a Sweep for each end?

Henry H

EDIT: I see the problem with this approach. There should be some twist in the transition, too.
« Last Edit: May 02, 2015, 03:16:41 PM by Henry Hubich »

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* May 03, 2015, 08:49:03 PM
#4
I'm finding this to be a real challenge. Here's my latest stab at it...

The twisted band in the first attachment consists of two Rail Sweeps with a Twist Angle (white and pale blue in the second attachment) and one with no twist (green). These were copied and rotated 180° about a Z axis located at the upper end of the set. Nonuniform twist was achieved by controlling the placement of nodes on the Splines used as sweep paths. (My article on Springs has a fairly detailed explanation of this technique.)

Henry H

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May 04, 2015, 04:40:42 PM
#5
Thanks guys this was different all right and most challenging.  It seems if you look at the simple things the more complex it really is.  Maybe in part that’s why projects evolve incrementally; otherwise Orville Wright would have made a 747.

Bob

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