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Rail extrude question (#305)
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rojharris  
#1 Posted : Wednesday, May 30, 2007 1:57:05 PM(UTC)
rojharris

Rank: Junior Member

Joined: 5/28/2007(UTC)
Posts: 15
Hi There,

I am a complete beginner with nurbs and I am having some frustrating difficulties doing what would seem to be a simple operation. I have bought ViaCAD (because it seems amazingly powerful for its price) mainly to model bottles (my client is a bottle product designer). Now very few of these bottles are your basic revolved profile round an axis critter. Usually they have different x and y dimensions, like an elipse. So here's what I'm trying to do:
I draw a cross section, like an elipse for eg. then I procede to draw the profile of the height of the bottle, starting with the recessed base bit, then down to the bottom, then out a bit, then up the side to the top, then in for the neck, then straight up then finish (with an interpolated spline). When I try to use rail extrude to skin the bottle shape I always get a "self-intersecting" errror.
How can I avoid this? Should I always use cross sections and skin them (but then how to get the domed recess in the base)?
This is very frustrating as I am sure there must be an easy way.

Here is a grab of a profile so you can see what I mean.

Any pointers much appreciated. I can't believe I'm stumped at the first hurdle on this one!

cheers
Roger
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rojharris  
#2 Posted : Thursday, May 31, 2007 2:18:33 AM(UTC)
rojharris

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Joined: 5/28/2007(UTC)
Posts: 15
OK. I've figured out, by looking at other software methods, that what I need to do is a 'boundary sweep'. Can I do this in viaCAD?
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jlm  
#3 Posted : Thursday, May 31, 2007 11:54:33 AM(UTC)
jlm

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Rojharris,
You're right, it's difficult to make it !
I tried all the methods I could think of to make a similar shape (one or two rail sweep surface, one or two rail sweep solid, solid skin with guides, guide skin surface...).
They all failed.:mad:
"self intersecting or cusping surface found".
I'm sorry, it doesn't help...

Hey Punch people !
What is cusping ?

JL
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jlm  
#4 Posted : Thursday, May 31, 2007 12:42:25 PM(UTC)
jlm

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Though, if you need to make this shape, use a set of ellipses (ie the one you have + a bigger one at the base + 2 for the body + one for the neck) and use the simple skin solid tool.
You can change the ellipses parameters afterward and get a very smooth solid.
I used this method for a few shampoo bottles.

The nurbs nerds should still fix the cusping :rolleyes:

JL
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rojharris  
#5 Posted : Thursday, May 31, 2007 1:54:47 PM(UTC)
rojharris

Rank: Junior Member

Joined: 5/28/2007(UTC)
Posts: 15
Hi Jim,

Thanks for the reply. I did make it with skinned elipses in the end, although I found it difficult to get the top nice and straight. Sometimes it's better to be able to define a clean profile so it's exactly what the design specifies, so I agree that this should be fixed! It would be ok if we could make it from cross sections and then afterwards edit a profile curve but I couldn't get that to work.

Of course this would be a doddle in sub-d's but then that's not the point.

cheers
Roger
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jlm  
#6 Posted : Friday, June 1, 2007 12:07:10 AM(UTC)
jlm

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rojharris wrote:
Hi Jim,
I found it difficult to get the top nice and straight.
Roger

Roger,
Then, make the top part with another solid (cylinder or extrude), boolean add and blend the junction.
JL
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