Lofting problem in Inventor

[cjt12b]

Hello,

I am trying to loft multiple sketches. All of my sketches are able to be lofted and extruded, but when I try lofting multiple sketches together, I run into some problems. When trying to loft, I can loft so many sketches, then it gives me an error message. I cannot loft all of my sketches together. The direction I seem to loft and what sketch I start at seems to be important. For the sketches that I can loft, the loft becomes unsymmetric even though all of my sketches are symmetric and all in line. I am not sure why I cannot loft my sketches all at once, and I am also not sure why the loft becomes crooked and unsymmetric. Is there a way to fix this? I am a college student and I have the student version from Autodesk, so I am not sure if this could be the problem.

Thank you for your help

[chrisjuk12]

Hi,

Lofting can be a bit of a problem when your not 100% sure of the correct process. Can you upload your model so that I can take a look?

Regards,

Chris

[cjt12b]

Yes. I will attach it in this post. Thank you for your quick response.

Clint

[wilkhui]

Hi Clint,

Welcome to the forum!

The sketches that you've created seem to oscillate around the type of surface you're looking for - I isolated a few of the sketches below and when I look at them head-on it shows the bumpiness in the profiles, which results in a bumpy loft, which eventually fails in the way that you're seeing because the oscillations create some very unfriendly curvature:

When I skip a couple of the bumpy profiles you can see that the result is a lot 'cleaner':

Hope this helps, let us know how you get on.

Cheers,

Indy

[cjt12b]

This makes a lot of sense, and I understand what is happening a little now. Thank you for your help. There are some sketches that I cannot skip though, because it produces a crucial feature in my design. Although skipping a sketch here and there does work, this still does not solve the problem of not being able to loft the whole thing at once and having it come out symmetric. I have edited each sketch to were all the sketches that taper from the front of my design to the widest point in my design are constantly growing and do not have conflicting lines that could cause a problem. I did the same thing for the back half of my design, by making sure each sketch continually was getting smaller and smaller with no conflictions. It still will not allow a continuous loft, and some of my sketches won't even loft, even though they can be extruded and are closed. Shouldn't I be able to loft everything all at once now, and what would be the cause of the sketches that can't loft?

Clint

[cjt12b]

Also, I get this error message when I can't loft.

The attempted Loft operation resulted in self-interesecting surfaces. Try with different inputs.

[wilkhui]

Hi Clint,

Sorry to hear that it still isn't working. Can you attach a part with your redesigned sketches?

Thanks,

Indy

[cjt12b]

Yes sir, thank you for your help. Those videos made a lot of sense. I reattached my file to this email with all of the sketches updated. It is somewhat hard to explain what is going on and what I exactly am trying to do, but to put it simply, these are my main goals and problems:

• I want to be able to loft all of my sketches together in order to form my design. Although some of my sketches can be skipped to help eliminate a problem here and there, this still does not allow me to achieve a final design that is straight and symmetric.
• My number one goal is to loft of the sketches together and the loft come out straight and symmetric. I am not sure why I can't loft all of them together and what is happening.
• The sketches that I am able to loft always come out a little twisted, not so much bumpy, but twisted in a manor that some what corkscrews (the left side of my design will come out different from my right side
• All of my sketches are closed and can be extruded, but not all of them can be lofted.

Sorry for the detail, but this is a strange problem that I haven't run into and none of my professors have either. Thank you very much for your help.

Clint

[wilkhui]

Hi Clint,

Forgive me for the delay in getting to this, is it ok if I get back to you on Monday?

Thanks,

Indy

[cjt12b]

Yes sir, that would be great. Thank you once again for your help, I really appreciate it. I have been stuck on this problem for quite some time now.

Clint

[JDMather · Accepted solution]

My opinion is that you are trying to do too much in one loft.

I think you would be better of by concentrating

Top Surface

Side(s)

Bottom as at least two separate features.

Trim and stitch or sculpt.

[mrattray · Accepted solution]

I don't really have time (today) to experiment with your file, but my 2 cents would be to draw only one half of the object and then mirror the whole body. This will be easier for Inventor to solve and will force symmetry.
My second suggestion would be to explore the use of guide rails. This will help to prevent the "twisting" effect.

[cjt12b]

Thank you, I have been experimenting with a couple of different options and luckily I have come to an answer. Because of the complexity of the loft going from each cross section, I decided to try and simplify my design. Basically, what I did was try to make sure each sketch was perfectly aligned, I tried to make the change in each cross section as smooth as possible, and what made the ultimate difference was deleted half of each sketch so that I only had one half the amount of lofting to do. This forced some symmetry as you said it would and made perfect symmetry. I then mirrored my loft and came up with the design I wanted. I am now ready to continue with my design.

Thank you once again for yall's help, as all the information you gave me helped to make a succesful loft. I truly appreciate it.

Clint