topic Re: Tricky 3D modelling concept in Fusion Design, Validate & Document Forum

Tricky 3D modelling concept

Anonymous — Fri, 05 May 2017 16:44:03 GMT

Hi all,

Really need some help. Long story short, I have a model I need to make, which was supplied on paper (rather as a PDF) as cross sections in 2mm steps. I have got these into Fusion as outlines, and I have stacked them up. I now really need to find a way of smootly linking between the cross sections, in order to make my 3D shape. Here is a link to a picture of what I mean:

If I loft each of them to meet the next, I end up with this, which matches the specification, but I want to 3D print it, and obviously it's not ideal for that:

I want a smooth representation of the shape, that hits the cross sections where it needs to at each 2mm step. Anyone know the best way to do this? I've asked and tried everything I can think of so fat, and I'm quite new to all this!

Many thanks for any help

Lee

Re: Tricky 3D modelling concept

etfrench — Fri, 05 May 2017 16:57:53 GMT

How did you do the lofting, individual for each layer or one continuous loft? I expect the later to give you a smooth shape.

Re: Tricky 3D modelling concept

Anonymous — Fri, 05 May 2017 19:07:42 GMT

Thanks for the reply!

I did the lofts individually... How would I go about lofting the whole thing? I want it to go from the bottom, via all the cross sections, up to the top.

Re: Tricky 3D modelling concept

SaeedHamza — Fri, 05 May 2017 19:20:53 GMT

Hi,

The loft command lets you choose as many profiles as you like, and then creates a smooth geometry between them

Regards, Saeed

Re: Tricky 3D modelling concept

TrippyLighting — Fri, 05 May 2017 21:02:14 GMT

@SaeedHamza is right, you can connect all those profiles in a single loft and then "might" get a smooth shape.

Whether that really works in reality is another question and depends to a degree on the precision on these profiles. Generally, using fewer control points/profiles creates a smoother shape.

However, I am wondering if that is not a rather inefficient technique to create a 3D model of a human ear in Fusion 360. Unless you are interested in exactly this particular model, this can be done so much more efficiently and with more control with T-Splines.

Re: Tricky 3D modelling concept

Anonymous — Sat, 06 May 2017 09:03:51 GMT

Thanks for the replies guys. I'm investigating the loft over all of them next, I think I may have tried this before though, I can't remember. This has been an ongoing problem for me!

The trouble is that I need this exact model as it's a specified model in a standards document. It's a dumb way of doing it, but they provide it in cross sections like that, so it's the way I have to do it 😕

Any other wisdom is greatly appreciated!

Re: Tricky 3D modelling concept

SaeedHamza — Sat, 06 May 2017 10:29:46 GMT

Could you please attach the file?

Re: Tricky 3D modelling concept

Anonymous — Mon, 08 May 2017 13:13:26 GMT

Hi Saeed,

Thanks very much for your help so far. As requested I have attached the archive file of the project, of the stacked up sketches. If I try and loft through the entire stack it gives an error for intersecting parts and doesn't work. If I do them individually, I eventually get to a point where the result of the loft is not right, and is jagged, folded back on itself and crazy. Not sure where to go from here, I'm just hoping it is possible.

I am still very new to this kind of thing though, so I'm hoping I just missed something really obvious!

Many thanks,

Lee

Re: Tricky 3D modelling concept

SaeedHamza — Mon, 08 May 2017 17:30:09 GMT

Hi,

I checked your file and to be honest it's a mess man 😛

Your problem is that your profiles are just too much, not to mention how different they are from each other

for example if you try to loft the first 3 profiles from the bottom it's fine, but adding the 4th is an error, and that's because of the difference between the 3rd and the 4th

so try to decrease the number of your profiles and make them more alike

Best regards, Saeed

Re: Tricky 3D modelling concept

Anonymous — Mon, 08 May 2017 20:05:23 GMT

Hi Saeed,

Thanks for looking at my file! Yeah, it's a mess. The trouble is that I can't add or remove profiles as they are supplied like that in the standards document, and I need to match that model. It's really dumb. I'm specifically trying to use this model to cheaply be able to use this type of model in my PhD project, so I need to figure out some way to do it. This is my 3rd 3D modelling software that I have tried 😞

Any other ideas or am I screwed / back to square one?

Many thanks,

Lee

Re: Tricky 3D modelling concept

SaeedHamza — Mon, 08 May 2017 20:33:53 GMT

Hi Lee,

You still have a chance of getting this right, you only have to fix you files so that they are similar to the ones near them

if you do that I assure you that it will work

check this screencast for better understanding

https://knowledge.autodesk.com/community/screencast/01105767-b33a-4332-82f3-23445453c00e

Regards, Saeed

Re: Tricky 3D modelling concept

TheCADWhisperer — Mon, 08 May 2017 20:41:43 GMT

Rather than attempting to loft those closed profiles as a solid - I would loft various surfaces and then stitch to a solid.

I would use Autodesk Inventor rather than Fusion, because I am more familiar with lofting in that software.

Re: Tricky 3D modelling concept

Anonymous — Thu, 11 May 2017 08:57:12 GMT

Wow, this screensharing feature is great!

Thanks so much for the run through of my project. I know what you mean, I have had the same problems with the dissimilar profiles not working properly, but the issue I have is that it has to match that physical spec. Quite a painful mission!

I will do my best with what I have. Thanks so much for the help! I also might give Inventor a try.

Thanks,

Lee

Re: Tricky 3D modelling concept

etfrench — Thu, 11 May 2017 17:49:40 GMT

2mm layers are really coarse for the size. One way you can try to resolve the loft problems is to add one or more layers between two problem layers. For example, between layers 3 and 4 the loft fails with self intersecting error. This is usually caused by an acute angle in the boundary. Try creating a middle layer, project the boundaries from the outside layers, draw a new boundary midway between the two. You may have to repeat the process several times to get a good loft between the main layers.

Re: Tricky 3D modelling concept

TrippyLighting — Thu, 11 May 2017 19:30:05 GMT

@etfrench wrote:

2mm layers are really coarse for the size. .

Generally the fewer control points are in a spline and the fewer profiles are in a loft, the smoother the spline, loft.

Re: Tricky 3D modelling concept

TrippyLighting — Thu, 11 May 2017 19:37:21 GMT

I would still convert this into a T-Spline with a method that might at first seem onorthodox and is definitely tedious, but will likely create superior results to any lofing attempts.

I am not at my Fusion 360 station at the moment and cannot try out if this works but I'd create vertial costruction planes with about the same 2mm distance as the horizontal profiles.

then I'd project/intersect where the curves intersect thes costruction planes.

the result is - again in theory - a grid of points that can serve to create T-SpLine faces.

You'd end up with a T-Spline mesh that should be a close approcimation of that earmodel. It will also likely be a closer approximation than a loft.

Re: Tricky 3D modelling concept

etfrench — Thu, 11 May 2017 19:37:16 GMT

@TrippyLighting wrote:

@etfrench wrote:

2mm layers are really coarse for the size. .

Generally the fewer control points are in a spline and the fewer profiles are in a loft, the smoother the spline, loft.

But the loft has to be precise and currently it isn't possible to create it.

Re: Tricky 3D modelling concept

TrippyLighting — Thu, 11 May 2017 20:36:50 GMT

More control points does NOT equate with more precision.

Re: Tricky 3D modelling concept

TrippyLighting — Thu, 11 May 2017 23:39:31 GMT

So I tried to approach this with T-Splines (create face with object snapping). Unfortunately not only is this ridiculously tedious, but when snapping the pints for faces to the profile lines the T-spline resulting from the operation is not going through the profile lines. So this is not very practical either 😕

Re: Tricky 3D modelling concept

SaeedHamza — Thu, 11 May 2017 23:58:43 GMT

man the more I try solving this the more it drive me crazy ...

these profiles are disastrous, they are not even moving in a right way like a spline, but still I wanna try something out

could you please send me the file that contains this shape you achieved in this image

Regards, Saeed