Trying to make a gusset for an eyelet

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practical
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Trying to make a gusset for an eyelet

Post by practical »

I've been trying several ways now to make a gusset for a toroidal eyelet, the desired result being this:

Image

The issue is, every way I've built this, something fails to fuse. Strangely, sometimes it will fuse at first, and then many boolean operations later, it will break. So, is there a way to build one of these robustly? Maybe a loft? Any ideas are appreciated, and I'm using FreeCAD 0.18.

Things I've tried so far, that I can remember:
  • Making the gusset a sketch, then extruding it, then filleting the edges. This had two problems. First, the fillet couldn't be the same radius as half the width of the extrusion, or it would fail. I made it 99.9% of that, and that worked at first, but later boolean operations caused issues.
  • Using two other tori (not full 360's, but 90 degrees each), and then using an extruded sketch to fill in the last bit left over. This is what you can see in the image above. Although the three tori would fuse, it would not work with the final fusion of the extruded sketch.
  • Using no torus, creating the whole thing from a sketch, and then filleting the necessary edges. This is very close to ideal, but you can't set the fillet radius to half the extrusion depth as that causes it to fail. If there's no better solution, I'll probably just use this with a radius 99.9% of half the extrusion depth.
chrisb
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Re: Trying to make a gusset for an eyelet

Post by chrisb »

You may upload the file you have to make experimenting easier. If you make a Part->CheckGeometry with BOPCheck enabled and you see errors then there is a high probability that later boolean operations will fail.
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practical
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Re: Trying to make a gusset for an eyelet

Post by practical »

I've attached the current file, stripped down to the bare essentials. The boolean works, but it's not ideal. The main problem I'm having with the current fillet method (the last method on the list in my earlier post) is when trying to analyze the object with FEM. I get "nonpositive jacobian" errors whenever I try to run the analysis, which I assume is because it's not a true torus and actually has very small "flats" in what would otherwise be a circle.
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hammax
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Re: Trying to make a gusset for an eyelet

Post by hammax »

… from torus to plane with an adaptive loft.

Eyelet.PNG
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Eyelet.FCStd
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practical
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Re: Trying to make a gusset for an eyelet

Post by practical »

My only issue with your method is that the hole is not a circle when viewed from the side:

Image

That said, maybe I just need to play around with placement and I might be able to get it to be circular.
freedman
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Re: Trying to make a gusset for an eyelet

Post by freedman »

Part design with a fillet.
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practical
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Re: Trying to make a gusset for an eyelet

Post by practical »

Thanks, that looks like it will work. I'm not as familiar with the part design tools, but it looks like they may be the best way to approach this.

I do wonder if you can replicate this using the other method though, by fusing a torus to the object first, and then filleting the edges. I'll have to test it out. Yes, this can be done in standard part tools as well, just fuse the torus with your object first, then use a fillet on the edge.

Edit: Not sure why, but I'm still getting nonpositive jacobians, so FEM isn't working. If anyone finds a way to fix that, or knows why it's occurring, please let me know. Searching around for other posts on the forum hasn't revealed why.
Last edited by practical on Wed Dec 11, 2019 9:51 am, edited 1 time in total.
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hammax
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Re: Trying to make a gusset for an eyelet

Post by hammax »

… also after some finetuning

Eyelet_2.PNG
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Kunda1
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Re: Trying to make a gusset for an eyelet

Post by Kunda1 »

practical wrote: Tue Dec 10, 2019 12:44 pm ...I'm using FreeCAD 0.18
practical wrote: Wed Dec 11, 2019 2:35 am Edit: Not sure why, but I'm still getting nonpositive jacobians, so FEM isn't working. If anyone finds a way to fix that, or knows why it's occurring, please let me know. Searching around for other posts on the forum hasn't revealed why.
If you want to use FEM it is recommended to use the 0.19 development version. What platform are you on?
(btw, please attach you Help > About FreeCAD > Copy to clipboard info to the first post (per the forum guidelines))
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bernd
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Re: Trying to make a gusset for an eyelet

Post by bernd »

in most cases it does help to use a smaler mesh size. Attached mode shape 9.


Screenshot_20191212_001922.jpg
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