Nice Hat! I'm hoping to become proficient with MoI as you. I have also been trying to do Sweeps and the rail thing.

I beleive it's the same as another modeler "Carrara" I use. creates a "Spline object" which has "Symmetry" lines for manipulation.



Seems as though the Rails option (Two Rails) represent the Extrusion path in the 2 planes? (Carraras shows 1 symmetrical pink line) and the "Scaling rail" represents the "Blue and Green" symmetry paths"?

I'v been trying to figure out the 2nd rail option.

From Carrara, The scaling rail is the one with 2 "Plane" options, and if you need to change the extrusion path (the rail) you would add a "Cross section" and new rail and continue. Have I equated the 2 the same?

I'm not getting the result with the second sweep rail I thought and trying to adjust as needed!

Any thoughts? (did my question make sense?)

Thanks Burr

Hi Ed, yup that Pod video has a good example on a scaling rail in action.

The basic idea is that when you normally do a sweep of something like a circle along a rail path, the result will be a very evenly sized tube.

That's great if you want something very evenly sized, but if you want something that flares out at the end or swells up or pinches down in the middle a bit, something other than just a very even tube, then that's when a scaling rail can help to make that kind of a customized tube shape.

You can also use more than one profile cross-section curve in the sweep to get a kind of similar result, like for example use 5 different circle profiles each of a different radius, as the profiles for the sweep and it will make a kind of bulgy tube as well.

But if you find yourself using quite a whole bunch of profiles like that, it is a good idea to switch to using a scaling rail instead, because it basically controls the flare of the sweep with one "side" profile curve (which is much easier to edit and tweak) rather than a whole bunch of individual circles of different sizes.

Here is a visual example:



The basic sweep there produced a very sort of "normal" tube, then applying the scaling rail in the last image shows how it stretches the sweep out until it matches that additional shape, making a bulge in the middle and flaring out at the end.

You can also use it in spots where you don't need such a dramatic flare or bulge bug still want some control over changing the profile gradually over the course of the sweep.

Please let me know if you need some more examples, that Pod video is a pretty good spot to see it though.

- Michael

Hi Burr,

> I'm not getting the result with the second sweep rail I thought
> and trying to adjust as needed!

Please post the .3dm model file with your curves in it that you are trying to sweep, that will really help me to see what problem you are running into and give you some advice on what to do differently.

I'm not really familiar with that Carrara tool, but it looks to be different from a sweep - a sweep in MoI is not really constrained to work relative to the x/y/z planes only, it follows the rail curves.

So that allows for stuff like this for example:



I'm not sure if that Carrara tool is going to be able to do stuff like that, if it is focused very much on editing from a side plane projection it probably will have some difficulty when a path wants to kind of loop around more freely...


To do a shape more like what you are showing there in MoI you would probably draw cross sections and then use loft, something like this:



It is possible to use sweep to do something similar with a straight line as the sweep rail, but Loft would probably be more typical for something like that.

- Michael

[EDIT] Just saw a reply as I posted, May answer my question.[EDIT]

Here I am trying to do a fishing led. I create the shape I want but need the neck to narrow in only one plane. this model has symmetrical polygone on both ends.

If anyone can point me in the right direction I'd much ablidge. Was trying to fool with (demo from pod) adding other profiles as it goes. I think this is right but still trying to squish my polygone (On the small end only, and for only 1/8 the length) asymmetricaly. How would I do this? (Scale in x/y only?)

Sorry it's so newb. Trying to switch my brain.

Thanks again,
Burr

Hi Burr, if I understand you correctly try switching the "Maintain height" option to be on (checked) for your sweep.

That's one of the options that will show up in the upper-right area of the screen when you are doing your sweep.

When "Maintain height" is on, it will stretch things only in the one direction towards the scaling rail which I think is what you are asking about?

When "Maintain height" is off, things will instead get scaled in a uniform way, getting bigger or smaller in all directions instead of just in the direction towards the scaling rail.

In your case you have the scaling rail running along the top of the object, if you wanted the squishing to be more lateral instead of vertical, then switch ot the right-side view and rotate your scaling rail 90 degrees so it is on the side of the object that you want the stretching to go in.

Please let me know if this doesn't make sense!

- Michael

Michael,
The Maintain height check does indeed produce the "squish" I am looking for, though, I want the symmetrical path for 7/8 the length and the "squish" for the last 1/8.

Heres a picture of the end result I want.

Hi Burr,

> though, I want the symmetrical path for 7/8 the length and the
> "squish" for the last 1/8.

There isn't any way to do maintain height only for just a portion of the sweep, it's either on for the whole sweep or off for the whole sweep.

But you could do the sweep in 2 portions if you want, with different options set for each portion, will that do what you need?

I'm sorry I can't quite follow what you want from those images, they're kind of dark. Is there any way you can describe it a bit more?

It may be possible for the case you are talking about here where you want shifts in behavior at different spots in the rail, that using multiple profiles would be a better way to go than using a scaling rail, but I'm still just not quite sure what your desired end result is though.

- Michael

Seems probably loft is more what I need. can I make my Polygon asymmetrical for the last inch? Probably more the newb question is how. Thanks for your time.

DO these show the difference in neck width?

Mutiple profiles and Lofting is my answer. Thanks again.

I'll post a new thread for my basic questions on "How to draw" for dummies.

Burr

Hi Burr,

> Mutiple profiles and Lofting is my answer. Thanks again.

You're welcome - sorry I didn't understand sooner.

Yeah if your shape is kind of following a straight line, then yeah sweep is probably not really very necessary.

However, sweep and loft are similar in some aspects, like you can also use multiple profiles for Sweep in the same way that you used them in Loft, it's just that sweep also uses a kind of "spinal column" rail to follow along.

- Michael

Is there somewhere that would tell me How you would do sweep in 2 portions with diiferent params for each?
Is this the second rail thing? Or, how is the second rail used?

I think this is what the original thread was getting at and I would like to know also.
Thanks.

Also, I think this is what was confusing me before. In the Carrara program, they have a sweeping tool that does the scaling rail, also with symmetry (your keep height check) and they ALSO do the cross-section lofting in the same area. Yours is split into 2. (yet dual functionality in both. sweet!)

Hi Burr,

> Is there somewhere that would tell me How you would do sweep in
> 2 portions with diiferent params for each?

Sorry I didn't describe that better earlier - to do that you would need to cut the rail curve into 2 pieces.

Then you would repeat the sweep twice, the first time picking one piece of the original rail, and then doing a second sweep using the remaining portion.

To cut the rail, select it and then run the Edit/Trim command. It will prompt you for "Select cutting objects". If you have a line or something that crosses the rail you can select it as the cutting object here, or you can also click the "Add trim points" button, which will then let you click a point on the curve to use that point as the split location.

After you have finished picking the cutting objects or cutting points, the Trim command will prompt you to "Select pieces to remove or push Done to keep all" - here just push Done (or right-click inside a viewport which is a shortcut for Done) because you want to keep all the cut-up pieces and not discard any.

So after doing that your sweep rail will now be cut into 2 curve pieces. Do sweep twice, using a different piece for each sweep and that way you can use different settings for each time you run the sweep command.

Please let me know if this doesn't make sense and I can make some illustrations.

- Michael

Very Clear, No need to illustrate this. Please when you have time, illustrate the "2 rails" sweep. I'm thinking this equates a way in my old modeler and want to be sure. ie;

Part on wall plane z.

first rail on wall plane x.

second rail on wall plane y.

???

When you have time.

I also posted a thread on our previous discussion here regarding sweeps and lofts. Please review my results!

Thanks,
Burr

http://moi3d.com/1.0/docs/moi_command_reference7.htm#sweep
(scroll)
PS You can select any numbers of profil before to choose the 2 rails
You are not obliged to put your profils on the rails! (they must be in the same plan)

Thanks Pilou. The old "look at the instructions trick". I'll mow through there a bit before I do any more irritating posts! The reference is enough for me to get started.

Thanks again,
Burr

RE: Scaling Rail

Thanks Michael.

OK - the scaling rail modifies the profile.

When would I use this as opposed to using using two rails with multiple profiles? Is this basically a shortcut to using two rails with multiple profiles?

Just trying to better understand when and where to apply the tools :)

Ed

My 2 cents ( and it is only 2) is that the sweep doesnt do well with more than a couple or few profiles. Multiple profiles would become a Lofting operation.

Eh?

Burr

Hi Ed, well you can actually use a scaling rail with 2-rail sweep as well, it's something that acts as an additional modifier on top of the basic sweep itself (either 1-rail or 2-rail).

If you find yourself trying to add a whole bunch of cross-section profiles to a sweep to try and control the side-view profile of it, that can be a good sign that you should be using a scaling rail for that instead.

Here's an example of that from a while ago:



You can kind of get the idea there that someone is trying to make the sweep fit to that guide curve that you see running along the upper part when viewed from the side.

But it can be frustrating to try to get the shape to match purely by adding more and more and more profiles, you may have to add quite an awful lot of them to control the profile and that tends to be a lot of work.

That's what a scaling rail will handle for you - it will pull those profiles up so that they match that additional "scaling" rail going down the center so you don't have to try and add many many profiles to try and get more direct control over the side profile.

Also, a one rail sweep with scaling rail is not quite the same process as a 2-rail sweep.


A 2-rail sweep works something like this - if you have 2 rails with a profile curve:



The profile will be moved by incrementally sliding it along each of those rail curves, so it will draw out a path something like this:



So one thing to note here is that the profiles are not necessarily always perpendicular to any one single rail curve, like here is a more exaggerated example:



You can kind of get an idea there how the profiles kind of slide around for 2-rail sweep. If you want something that is guaranteed to be a perpendicular construction off of a single backbone or spinal-column type curve, then one rail sweep will do that - it will move the profile curve along that spine curve and be perpendicular to it at every spot.



With 2 rails it just is not physically possible to be perpendicular to both rails at the same time at every spot unless your curves happen to be offset curves from one another.

Now when you use a scaling rail with a 1-rail sweep, it keeps the perpendicular-to-spine type arrangement and then will shrink or expand those profiles still in the perpendicular direction. So for example if this is the scaling rail that is added to that one rail sweep:



The profiles will get then expand in this kind of manner:



So one-rail sweep with scaling rail does not "slide" the profile along the scaling rail, it only slides along the spine rail and then grows to intersect the scaling rail, that's what is different about it from 2-rail sweep.

Hope this helps!

- Michael

Hi Burr,

> My 2 cents ( and it is only 2) is that the sweep doesnt do well with
> more than a couple or few profiles. Multiple profiles would become
> a Lofting operation.

It all kind of depends on what areas of your result you want to have control over.

If you want something that has a kind of automatically calculated "tautness" in one direction, then Loft should work well for that.

Like for example if you take these 3 circles:



A loft will build a shape like this:



It's sort of passing through those shapes in a kind of minimal smooth way.

If you wanted to control more details of how it is shaped as it is marching along in the "lofting direction", then a sweep will let you get more control over how the sides are shaped, like for example:



You could get that with just doing Loft by adding in a whole bunch of circles, but it is easier to draw a curve to use as a rail for sweep to get more control over that.

If you need additional shaping control, then use sweep, otherwise if you don't need exact control over that side shaping, then Loft is more likely the way to go.


(By the way, for doing things made up of all perfect circle sections actually doing one profile and using revolve is easiest for that, but still this example should show the right idea I hope).

- Michael