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 From:  NightCabbage
2879.1 
Ok, so I'm doing things to get my brain into thinking what the best way to create shapes with NURBS is - so I decided to make my own sphere.

I decided to make it by sweeping a circle along a line, and using an arc as the scaling rail - as the following picture shows...



It kind of worked... it made a sphere, but as you can see below, it gave the sphere a circular cap at each end - and I'm not sure why it would do this...?



I played around with the sweep options, but none had any effect on the circular caps.

EDITED: 26 Aug 2009 by NIGHTCABBAGE

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 From:  Michael Gibson
2879.2 In reply to 2879.1 
Hi NightCabbage - really the easiest way to manually make a sphere is to have a 180 degree arc and then use Construct / Revolve to revolve it around an axis, with the pivot axis being the line between the arc's end points.

The "scaling rail" option in sweep tends to be rather sensitive to areas where the scaling rail collapses down and actually touches the main rail like you have in this particular case.

Also the scaling rail should cover the entire length of the sweep - if the scaling rail is a little shorter than the rail then it would also make the kind of result that you show there so that may be a possibility as well.

It's hard for me to know for certain without seeing the actual 3DM model data - if you have problem it actually helps quite a bit if you would also post the 3DM file instead of just a screenshot, because then I can more closely examine the geometry to see what is going on.

Check out this previous post for some more description and illustration of how the scaling rail option works:
http://moi3d.com/forum/index.php?webtag=MOI&msg=2681.3

Hope that helps!

- Michael
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 From:  NightCabbage
2879.3 
Here is a link to the file with my 2 sweep attempts :)

sphere.3dm

(note: version 1.1)
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 From:  Michael Gibson
2879.4 In reply to 2879.3 
Hi NightCabbage, thanks for posting the file.

It looks like you have things lined up properly, so that was not the problem.

The problem is just that the scaling rail mechanism is not suited for this kind of situation where there is a kind of "cliff" in the scaling rail. See this previous post for some more explanation:
http://moi3d.com/forum/index.php?webtag=MOI&msg=1807.7

Instead of using a scaling rail, use Revolve instead for this kind of a thing.

The scaling rail is more for adjusting things to control how a shape bulges as it travels along a rail, it doesn't really work well for collapsing down to a squished down point like you've got here.

- Michael
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 From:  NightCabbage
2879.5 
Ah, I think I understand it now :)

May I suggest an idea?

Instead of the profile defaulting to 100% of the profile size when the scaling rail runs out, couldn't it just either continue at the last known profile scale, or be 0?

Ah maybe that's a silly idea? Not sure...
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 From:  NightCabbage
2879.6 
Ok so another question...

Say if I'm making a shape - like a cylinder but with one end larger than the toher (like a cone without the sharp end).

I make it out of 2 circles, a small one and a large one.
Then I apply a loft.

Nice, there's my shape.

But there's also those 2 circles that I used to make the shape - they're still there. When I move or change the circles, the shape changes, too.

So my question is this...

Am I supposed to keep the circles after I've used them to make my shape?

Or should I delete them?

What if I want to be able to change my shape later? It seems to be easier to change the shape using these 2 circles than it is to change the shape by itself...

A fundamental question :)
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 From:  Michael Gibson
2879.7 In reply to 2879.5 
Hi NightCabbage,

> Instead of the profile defaulting to 100% of the profile size
> when the scaling rail runs out, couldn't it just either continue
> at the last known profile scale, or be 0?

It's a good idea, but unfortunately hard to fit in with the way sweep actually works.

It doesn't really go "inch by inch" along the rail, as it is building the sweep it can kind of bounce around and sample many different points as it refines the result. So "last known profile scale" is not really so easy to know.

Being 0 at all spots that are not intersected with the scaling rail would run the risk of making a degenerate surface that was all squished down so it looked like a curve... It's generally possible for surfaces to be squished to a point at their very end (just not with this particular scaling rail method) but it's not good for more of a length of a surface to be squished down degenerate like that instead of just the tip.

- Michael
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 From:  Michael Gibson
2879.8 In reply to 2879.6 
Hi NightCabbage,

> When I move or change the circles, the shape changes, too.

Yup, there you are seeing "construction history" in action - when you did the loft, the result surface remembers that it was built by a loft between those 2 input curves, and later on if those curves change the loft is recalculated.

You can disable that update if you want by selecting the Loft result and going to Edit / History / Disable update.


> So my question is this...
>
> Am I supposed to keep the circles after I've used them to make my shape?
>
> Or should I delete them?

Well, it depends on what you are planning to do.

If you think you're going to tweak the shape later on, then you would probably want to just hide them rather than delete them.

It does tend to be good to at least hide them to get them out of the way so that they don't interfere with things like selecting edges.

But the construction history function is limited in several ways, currently once you do something like a boolean or trim of the surface, the history will not be connected up anymore. So you may want to do something like apply your tweaks to those curves soon after you created the Loft and then delete them.

- Michael
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 From:  NightCabbage
2879.9 
Thanks Michael :D

Also, another question...

So I now have my shape, made form the 2 circles lofted...

But now I want to do withngs with it, like rotate and move it.

The problem is that to do this accuratly, I need to know the center points of the object - and these points (for snapping) don't seem to be present.

So I have to go and manually create my construction lines just to get the center point of each object I want to do something with, because there are not points to snap to :(

Anything I can do differently here?

-EDIT-

I've uploaded my file, in case you want to have a look at it :)

engine.3dm
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 From:  Michael Gibson
2879.10 In reply to 2879.9 
Hi NightCabbage - if you want to move your object so that its center is situationed in a particular area, you can use the Transform / Align command to do that.


> So I have to go and manually create my construction lines
> just to get the center point of each object I want to do
> something with, because there are not points to snap to :(

But for what reason are you so focused on requiring the rotation point to be at the center of your object?

If you want to just rotate your object to be angled somewhat, you can do that by picking just any point as the rotation center, it doesn't have to be the center of your object...

Maybe if you could describe a bit more about what kind of result you are looking for it would help me to understand.

But also there is a completely new edit frame for handling rotation and scaling in v2 which makes it easier to rotate around a center point. These are small grips that appear around the outside of selected objects, which allow them to be manipulated similar to how the bounding frame works in 2D illustration programs.

For some more info on that check out the top of the v2 release notes here:
http://kyticka.webzdarma.cz/3d/moi/doc/V2releasenotes.html

- Michael
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 From:  NightCabbage
2879.11 
Aha! You solved my problem twice :D

a) align

b) V2

Thank you!

-EDIT-

Hmm I was wondering... what about nudging with the arrow keys?

Say if I wanted to move an object just a small amout in one direction, is there a way I can just use the arrow/cursor keys to do that?
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 From:  Michael Gibson
2879.12 In reply to 2879.11 
Hi NightCabbage,

Re: Nudging with the arrow keys - yes it is possible to set that up by installing a plugin, see here: http://kyticka.webzdarma.cz/3d/moi/#Nudge

There are a variety of plugins and scripts that you can add in which are listed here:
http://kyticka.webzdarma.cz/3d/moi/

- Michael
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 From:  NightCabbage
2879.13 
That's great! I love nudging things :)

Now, just in case you're not sick of all my questions yet, I have another...

I guess this is still related to my background with poly-based 3d modelling.

Say in that previous file I uploaded, the engine, what if I decided that I wanted the engines to not be quite so "recessed" (or to be more recessed) in the model?

So what I'm saying here is "what if I wanted to move the following surface backwards and forwards"...



So thus I guess I mean moving the surrounding edges. Can I do that?

This is important, because it is my flow of work... I make an object that's basically what I want, and then I edit it later to make it exactly what I want.
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 From:  Michael Gibson
2879.14 In reply to 2879.13 
Hi NightCabbage, you would generally make adjustments like you're talking about in a similar construction type way.

For example to "move that surface forward", you could select it, then run Construct / Extrude to build a new solid coming out from it, then select that new solid and the original one and do a boolean union to combine them together.

That kind of an approach of constructing an additional piece and booleaning it with your model would be the most regular way to do that kind of an adjustment in MoI.

But it is also possible to break things into individual surfaces and do a lot more "low level" kind of tweaks at the surface level. If you want some more information on doing that kind of a thing, check out this object repair tutorial here:
http://moi3d.com/forum/index.php?webtag=MOI&msg=446.17

But it does tend to be better to build your object more closely to what you want earlier on, rather than just make something sloppy and tweak it later like you might do in a polygon modeler.

If you want to do the "tweak a bunch later" kind of workflow, probably a polygon modeler is going to be a better fit with that style of modeling rather than MoI.

- Michael
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 From:  NightCabbage
2879.15 
Oh well that sounds good :)

I guess I'm just trying to minimise my use of booleans, because in poly modellers booleans are horrible and don't work half the time.

But if I can rely on the boolean in Moi to work all the time, then that sounds great :)
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 From:  NightCabbage
2879.16 
Alrighty, so I've unioned the engine block with the 4 jets.

And the 4 jets have a circular hole in them, where you can see through to the back of the engine block.

So I've selected the circles of each of the 4 engines, and used the Planar tool to create a circular plane to cover these holes.

This is good, except that these 4 circular planes are not attached to the engine...

And I don't know how to attach them. Union just removes the circles, and join won't work on objects.

So I'm wondering how I can do this?
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 From:  BurrMan
2879.17 In reply to 2879.15 
Cabbage,
A good tip to remember with your solids also is the "Seam edge". When you create a sold to use, before you do anything, try to have that seam edge rotated out of the way of other operations. It's not a must, but in certain circumstances having 2 seam edges exactly graze along each other can cause problems. Like if you create a sphere and align some other cutting object directly on that sphere seam edge, then try to fillet that edge, you "could/may" experience poor results.

Again, just a good habit to develope when starting out.
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 From:  BurrMan
2879.18 In reply to 2879.17 
Here's Cabbages Engine file with the Exaust turned into solids and booleaned on to the engine. I tried to disable history on all objects from the beginning. If I select just the face of one of the exausts and run shell, it appears to try and shell All the exausts. If I select all exaust faces and run shell I get a good reslt ( .1 as the defined thickness).

Seems like something is up with his model? Possibly I missed an area I should have hit disable history? I started with the model he posted.
I ran planar on the whole group of exausts to cap them off. Perhaps if I planared them seperatly. I can fool a bit more also.

EDITED: 19 Jun 2012 by BURRMAN

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 From:  NightCabbage
2879.19 
Thanks for the reply!

What's Shell?

Ok so I figured that part of my problem was because I wasn't using solid objects (for the exhausts?)

And I figured out that another of my problems was that I was trying to boolean some things together when I should have been joining.

So you boolean intersecting solid objects, and you join touching lines.

Here's my new version :D

engine3.3dm

Maybe someone could check it out and see if it's done right?
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 From:  Michael Gibson
2879.20 In reply to 2879.15 
Hi NightCabbage,

> I guess I'm just trying to minimise my use of booleans,
> because in poly modellers booleans are horrible and don't
> work half the time.
>
> But if I can rely on the boolean in Moi to work all the time,
> then that sounds great :)

Yeah, that's one of the major differences between NURBS modeling and polygon modeling - booleans are much more robust and you usually focus on using them as a primary method of construction in NURBS modeling.

- Michael
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