#1 By: Ray Watson, August 20th, 2013 06:11
I have been working my way through Rhino tutorials, and am doing the one where you loft two surfaces, then trim them. I have attached the part of the instructions that I find incomprehensible.
I cant understand
1. Why you have to draw a line 1/2" "towards the hull surface"
2. What "towards the hull surfaces" means
3. Why trimming the two surfaces results in warped panels.
If anyone can shed some light on the process, it would be really appreciated
#2 By: Pascal, August 20th, 2013 12:10
Hello- it depends a bit on what happens later on but I suspect the trim line is off center so that a) it will not fall exactly on the edge of the target surface where that edge falls on the centerline- this would make a cleaner trim all along the length of the surface rather than a trim which sweeps gradually into an untrimmed edge. Just a guess. b) trimming off center will leave a small gap when the hull surface is mirrored and it may be that there is a step further along where a blend surface is created to fill that gap smoothly.
#3 By: David Cockey, August 20th, 2013 15:01
"toward the hull surfaces" refers to the side of the centerplane which the side and bottom have been created on.
The hull surface is trimmed off-center so there will be a gap in the middle after the side and bottom are mirrored. This gap is filled with the keel surface. See p106 of the tutorial in the Users Guide.
"3. Why trimming the two surfaces results in warped panels." - Can you elaborate on your question? Are asking why the trimmed panels don't coincide with the stem curve? It appears that you are using the "developable" option in the Loft command which is appropriate for a boat which would be built from plywood or sheet metal. The shape of the lofted surfaces at the ends depends in part on the shape of the curve extensions. Note the direction of the isocurves in the image you posted. The shapes of the ends of the lofted surface can be changed by changing the shape of the curve extensions.
#4 By: Ray Watson, August 21st, 2013 06:17
Thanks gentlemen, those suggestion were very helpful. The comment about the 'developable' option during loft did make a big difference.
The detail on the exercises is quite miserable, obviously they have never been tested on new users.