Help with Sweep Tool with Rails

[Anonymous]

Hello,

I am incredibly new to Inventor and trying to create a model to 3D print for school (I do have some experience with Fusion360, but the project requires that I use equation based lines, so I am using Inventor here). I have used the equation based lines to make two 2D bases, which I then want to sweep across with a semicircle to create a 3D shape (the semicircle diameter changing throughout, giving a different cross sectional area at each point). To do this, I am trying to do the sweep with rail function so that one line of the base shape can be the path and the other guide the semicircles to fit within the created bases. Whenever I try to do this, although fine for sweeping without the rails, I get an error. This is the case with any segment of the shape(s) when I try to use rails. Ideally, I could just have two work planes for each base shape (4 total) and scale both shapes up once the semicircle has swept across each so that the length of the big piece is about 7" and small piece about 4".

Would anybody happen to know what is giving me the errors and how to best move forward? I have attached a screenshot and the part file as that seems to help a lot within other help posts.

Thanks!

[tmoxam]

you are trying to Loft not Sweep.

a loft requires a series of sketches (profiles) that are strung together. (usually sketches are parallel-"ish")

you could for example create a series of parallel planes and then put a sketch on each one and then Loft them together.

a sweep requires a sketch with a 'path' that is perpendicular to the sketch with the profile that you want to Sweep

[WHolzwarth]

Basically your sketches are not precise enough.

- Curves need to meet in a single intersection point. Some position in the neighborhood will not work
- That's true for sketch planes, too. You've placed them near some endpoints, but not coincident with them
- Best results can be achieved with tangential transitions between curve elements. Not good between Equation Curve3 and Equation Curve5

[johnsonshiue]

Hi! Please share the part here. This should be either doable or not doable (bug or limitation). Without the file, it is impossible to tell.

Many thanks!

[Anonymous]

Lofting sounds like a good backup plan, but it would also be a royal pain to do and less accurate, as in this instance it appears that lofting would just be the equivalent of sweeping with checkpoints, no? In math terms, I am currently viewing this somewhat like the difference between an integral and a Riemann sum. Also if I were to try to loft, the rails still do not work as intended, giving me an error (1). This is the case besides the fact that I could loft without rails (2). I am also not entirely sure how I would do the end points of the shape without doing a really small cross section close to the end (on the inside of the shape) and lofting to it, which again adds inaccuracy. Pictures and the files are included (and labeled) showing a section to demonstrate what I mean, and I did close the shape in these images and files like a later comment suggested.

1)

2)

Thanks for your help though!

[Anonymous]

a) Ah, yes, my apologies, I forgot to close the loop on this file (I redid it from an older one to see if I might have accidentally clicked something somewhere along the line that would have caused the error). I closed the shape, but it still does not work.
b) The edge planes were more for me than for the design, sorry again for the confusion. I am trying to use a middle plane to sweep in both directions. That way, I can start with one initial semicircle cross section and sweep along the curve. This would, I think, make the other planes redundant, so I would only need the one central plane (with the semicircle) to intersect the base shape, which I believe it does. If I am still being unclear on what I am trying to do (which I might be and I apologize for that, still trying to merge the math/CAD parts of my head a bit), this link might explain it better, checking the semicircle and solid boxes and making n=49: https://www.geogebra.org/m/nKbHnter. I want to do this but with n=infinity and starting with a semicircle cross section in the middle.
c) Noted, but the rails are not working at all (even in segments that are not using that curve, where I am only going one way). If this issue is resolved but the curves being not lined up tangentially as you state creates another problem, I can probably change the curves to be tangential in their transitions without drastically changing the shape. My first priority is the rails.

All this being said, I can sweep without rails on both parts of the shape (top and bottom) (1&2). It is only when I try to use the rails that it gives the error (using either the top or bottom part as the rail) (3). Pictures and the file are attached (and labeled). The additional planes with another semicircle in the picture and file are for trying with lofting (which also does not work with rails), but I theoretically would only need one plane and the base shape, at least as I am picturing this in my head.

1)

2)

3)

Thanks!

[Anonymous]

Hello! I would guess this is probably just my inexperience with the program over a bug, but I have attached the file both to this reply, and it is attached to the original post. Some of the pictures in the other replies might help you gauge if it is a bug or a me problem as well. Thank you for any help you can provide!

[johnsonshiue]

Hi Spencer,

Sorry I did not see the part attached to the post! I took a look. There are a few places I would do differently. First, I don't think you will get the desirable shape using one feature or two. You need multiple features in this case. More than likely you need to use Loft. However, the Loft sections need to intersect with the section rails on the boundary. Also, the section rail needs to be tangent continuous.

I think you will be better off using Freeform environment. Then tweak the shape as you go. I will take a closer look and see if I can find an easier workflow to get the shape.

Many thanks!

[johnsonshiue · Accepted solution]

Hi! I took a closer look at the sketches. Based on my understanding, these curves are more like conceptual curves. You are playing around with concepts. I don't believe Inventor is the right tool for such exploration. This is because Inventor is a precise modeler. The objective of using such tool is to create the ideal shape for manufacturing.

There are still some workflows allowing you to play around, such as Loft or Freeform. In attached file, I used the profiles to create a Loft. Then convert it to a Freeform surface. There are a few tools to manipulate the shape. Please take a look.

Many thanks!

[Anonymous]

Hi,

While the curves were originally conceptual, I was then trying to bridge the gap with Inventor to make the real shape to 3D print (in which case the curves would be the perimeter of the shape). That said, after looking more closely at what you did, that was incredibly helpful, and I managed to create more cross-sections and loft together an even more precise version from your freeform, which meets my needs. I am accepting this comment as a solution as a result, and I really appreciate your, and the other commenters's, help.

Thank you!