Maybe in this order
bottom form with big fillet
top form with little fillet
Loft them

Run edit-seperate on the upper curve and choose the segments between the fillets in this area:



Run "rebuild" on these (or just delete them and reconnect with a single line) and rejoin, then run the loft command...

Hi Alex, so like Burr mentions, the problem you're running into there is due to your 2 curves having a different number of segments between them.

You can see the segments by using the Edit > Separate command on the curves - after you do that you can see that some of your straight line pieces on the upper piece are actually made up of a few pieces instead of just 1 line, as shown in Burr's screenshot above.

When you loft between curves that have the same number of segments in them, MoI will match up the curves segment-by-segment. If they have a different number of segments, then the curves are matched just by distance along whole curve and will produce the kind of result that you were seeing.

So if you edit your curve so that you only have single segments in those areas shown above, then your Loft will work with the kind of matching that you want. You can either use the Rebuild command like Burr mentions above, or you can also just delete those pieces and draw in a new line there so that you've got just one segment for those straight pieces instead of multiple sub segments.

I've attached the fixed up 3DM file here - if you use Edit > Separate on the curves in this file you can then select pieces and see that the top one is not broken up into multiple pieces in those areas where your original one was.

See this other recent post for another description of the same kind of thing:
http://moi3d.com/forum/index.php?webtag=MOI&msg=4214.1


Also sometimes to get more specific control over how things are matching up it can be good to do the loft between smaller pieces instead of between long curves too. But you can do it between long curves if you have the segmentation of each curves set up to match each other.

- Michael

So we must have at any time same number of segments between 2 curves lofted?
So why the mecanism is not automatic (about number of segments) ?

Hi Pilou,

> So we must have at any time same number of segments
> between 2 curves lofted?

Only if you want to have control over which specific parts of each curve is connected to the other.

If you have the same number of segments, then each segment is matched to the other corresponding segment - for example segment #1 on the first curve is matched to segment #1 on the second curve.

You can still make a loft between curves that have a different number of segments between them, but when you do that the matching will happen by a distance traveled along each curve, which will not necessarily match one small feature like a rounded corner with another rounded corner of a different length on the other curve. Having connections just by traveled length can make for a kind of twisting effect when there are small localized features between the curves.

See this previous post for some more illustration and explanation:
http://moi3d.com/forum/index.php?webtag=MOI&msg=4214.1


> So why the mecanism is not automatic (about number of segments) ?

There is an automatic mechanism that will be used if there is a different number of segments, but remember that MoI does not have artificial intelligence and so it's not really able to analyze curves and identify particular small pattern features that you would like to have matched - for example it's not able to just look at 2 long curves and automatically recognize that you'd like to have 2 smaller sub-regions of different lengths (like the rounded corners in this case) to be matched with each other.

But if you have the same number of segments between the curves, then MoI will be able to match things segment to segment.

So it's not required to have the same number of segments, but it can help to have it if you want to have some particular zone of each curve matched to the other instead of just having them connected by length traveled along the curve.


The other way you can control these things is to do lofts between smaller sections at a time, instead of doing the loft between 2 long curves that have various small sub features within them like rounded corners. If you do the loft between smaller sections (like between each separate feature), that can help you to control how the curves are being connected together instead of them being connected just by distance traveled along each curve.


- Michael

thx for explanations
an easy way is duplicate the curve make some deformations without add segments then make the loft

Hi Pilou,

> an easy way is duplicate the curve make some deformations
> without add segments then make the loft

Yup, that will make the result have the loft created with each segment matching the corresponding segment in the deformed curve.

Basically when there is the same number of segments between 2 curves, then the loft is the equivalent of doing the loft between each pair of segments separately and having the results joined together.

- Michael

BurrMan, Michael Gibson: thank you so much!

I understand that the program itself can not figure out what to do in a given case. But if such curves a lot, what do you do? Each curve will have to edit?

As I recall, in Google Sketchup no such problem, although there is another principle of modeling - the polygon.

In any case, thanks again for your help!

Hi Alex,

> But if such curves a lot, what do you do? Each curve will have to edit?

Well, instead of editing each curve, it's actually better to not create a curve like that in the first place.

So for example instead of drawing those parts with several different lines, just draw a single line for those straight areas of those curves.

You definitely want to make your initial curve structure to be nicely and cleanly constructed - any kind of messy structure in your initial drawn curves will tend to create correspondingly messy surfaces...


> As I recall, in Google Sketchup no such problem, although
> there is another principle of modeling - the polygon.

As far as I know there isn't any kind of similar loft tool in the regular Google Sketchup program, it is based more on creating straight extrusions, so there isn't really an equivalent operation that involves this kind of matching between different curves.

The overall method of operation is quite different between MoI and SketchUp.

- Michael