Circular Pattern using Loft Not Perfectly Aligning with Other Circular Patterns

[sdfiguer]

Hello! I am a novice with Fusion 360 and I wanted to try messing around with the program to 3D model a few objects I think are cool in order to improve and sharpen my skills. One of the objects I've wanted to model is a dodecahedron pentagonal-face nanostar with divets (picture attached). 

My process is shown in the pictures attached. First, I made a dodecahedron using the surface tool, then I created identical sketches on two adjacent faces to create the divets. I lofted this sketch to a single point and achieved what I wanted. Then, I tried to proceed using the circular pattern tool to replicate these divets, but upon using it, I found that it somewhat achieves what I want but not perfectly. As can be seen in the pictures attached, the divets don't align and intersect at the same point. Rather, they seem to be off by a very small amount, and this amount compounds as I utilize the circular pattern tool until it's not a perfect nanostar dodecahedron.

I should note that I have tried all three circular patterns: Adjust, Identical, and Optimized. All three give the same result. I also have made sure the axis for the circular patterns on each face are directly perpendicular to the center of each pentagonal face.

What do I do to have the circular pattern tool work for me? I of course could go in manually to each face, make a sketch, and loft until my eyes bleed, but I really want to know if I am doing something incorrect, or if there is a more optimal way to 3D model this object.

Any help is appreciated, thanks!

[g-andresen]

Hi,

here are some tutorials 

günther

[davebYYPCU]

Blue sketch lines does not inspire confidence you have the correct centre point.

[TheCADWhisperer]

Can you File>Export your *.f3d file to your local drive and then Attach it here to a Reply?

[Oceanconcepts]

Far more helpful than the screenshots would be if you could attach the f3d file. Export, choose f3d (Fusion Archive), then attach the resultant file. We should be able to see where the inaccuracy comes from. 

Are your sketches constrained to a fixed point, say a reference to the origin? 

[sdfiguer]

Here is a .f3d file for my part. Despite the blue sketch lines, I think I have the correct center point, but I could be wrong. I checked and it seems correct to me. 

[sdfiguer]

Attached in new reply! Thanks!

[davebYYPCU]

There is a gap in the seam of the first pattern, 

blue lines in sketch 1, 

how do you know you have the right centre point?

[Oceanconcepts]

I’m not able to work through what you have done right now, so my comments are based on just a quick look… When you have elements that have moved or have gaps as noted above, and then base sketches or construction references off of those bodies, it’s pretty easy to get inaccuracies that compound.  

Getting your sketches to be fully constrained (black) and ideally defined in relation to elements that won’t move (like the origin, or construction planes or other elements that remain fixed) will help ensure that the geometry works as you want it. You have several instances of yellow warnings in the timeline that indicate where references have been lost. It’s best to roll back the timeline and make sure those get fixed. Axis 4 is placed at a point where edges don’t join, for instance. That underlying geometry should get repaired.

This class recording does a good job of illustrating why you want to be careful about how sketches are defined and constrained. It might help you to rethink the approach to this kind of design. 

https://www.autodesk.com/autodesk-university/class/Debugging-Your-Fusion-Design-Lets-Get-Rid-Red-and... 

[KristianLaholm]

Everything is about a solid base to build the geometry on.
There is an earlier post with link to my "tutorials" on how i create geometry in Fusion and i included my tries creating the geometry you want.

I can't find much info on these "nanostars" but I think you are starting with the wrong solid.
The Dodecahedron gives a solid that feels "flat" starting from an Icosahedron and growing the center of the triangle faces gives something that looks more like the picture.

Dodecahedron start:
Starting from Dodecahedron

Icosahedron Start:

Starting from Icosahedron

Slightly different workflows used to create the 2 solids, have a look in the files and I hope they can inspire you.