Creating solid pentagonal panel from geometry? Spherical Dodecahedra

3dprinting
sketchup
geometry
sphere
modeling

#1

I am working on a project that involves creating a spherical dodecahedra using 12 pentagons glued to a 3 inch plastic sphere. I need to be able to create a 3D printable part (which will be printed 12 times) and I am having trouble figuring out how to make a solid part out of the geometry that I have so far. I am pretty new to 3D modeling in general so this may end up being something very easy for someone with a bit more knowledge of SketchUp.

I have created 2 spherical dodecahedra. One of them is three inch and the other is 3.25 inch. I then joined all vertices from the smaller dodecahedra to the larger. The part that I am struggling with is creating a solid part out of just one of the panels. I want to be able to increase the size of the interior sphere as well as the depth of the panel incase I end up using a smaller/larger plastic sphere or if I decide to make a thicker/thiner shell.

Any help would be greatly appreciated! Hopefully what I am looking for makes sense. :slight_smile:

I have attached the file that I am currently working from.

Dodecahedron_3.skp (1.2 MB)


#2

Nice modelling!

To get a solid panel:

Explode everything to all raw geometry.

Window select (left to right) around one panel. Cut to clipboard.

Delete everything else.

Paste clipboard contents back in place.

Go round each panel edge, and draw a line across between opposite vertices once, to create a face on that edge. Delete the line (the face should stay).

When you’ve done all five edges, Reverse or Orient faces, to get all front faces pointing out.

Select all, and make a component. Save As…

Here’s the result, with the axes reset to the centre of the sphere:

Pentagonal shell section.skp (161.1 KB)

Remember, to view it AS A COMPONENT, Import the file, don’t Open it.

You may want to reorient the axes for printing.


#3

If you want to change the size of inner or outer spherical face, I THOUGHT you could try selecting just that face, then using the Scale tool.

But it doesn’t work - I can’t get the centre point on the corner of the Scaling box.

Haven’t time just now to try any alternatives.

One to experiment with is to draw another sphere of the changed radius, then either Intersect it with the shell (if you want it thinner), or delete the inner face, then extend the radial lines towards the centre of the sphere till they meet its surface.

Then do as before - window select the new shell piece, cut to clipboard, delete the rest of the sphere, paste clipboard in place, and remake into a component.


#4

You are awesome! Exactly what I was hoping for and a very quick reply. Thank you!


#5

That makes sense. I will give it a go and see what I get. Thanks again for your help!


#6

Not at computer, but another thought.

Does the inside need to be spherical? If you don’t need to assemble it round a sphere, you could make the inside a flat Pentagon at any ‘radius’ from the centre.


#7

Yeah, the inside has to be spherical as the project is dependent on gluing panels to another thin shelled sphere.

I was just thinking of something else that may be an issue. Since the original design had it where the panels shared the same side walls, I might need to take this into account and make the panel slightly smaller before I print as it might make it where the panels don’t fit together into a perfect sphere. Does this make sense or am I seeing something that isn’t a problem?


#8

It depends on how accurately your printing process works. If it makes everything slightly oversize, for example by half the size of the print nozzle (if it’s an extruder), then you might need to allow for that. But try without first.

Have just worked out how to scale the radius.

Draw a pentagon round the inner points (five lines, to make a pentagonal face).

Draw two diagonals, to find a pentagon centre point.

Draw a line from the centre point to the component origin at the centre of the sphere.

Delete the pentagon and diagonals.

Change axes so the red axis is along the radial line from centre to origin.

Mirror (TIG Mirror plugin) the inner face about the central blue/green plane.

Then select both the original inner face, and the newly mirrored face, and Scale about centre to change the radius.

Delete the extra lines and face when done.

Will post GIF animation later.


#9

OK, I think I understand what you explained. The GIF will be really helpful. Thanks!


#10

I think there’s a small glitch in this but it shows the principle. There shouldn’t be an extra line on the ‘top edge’ face. Probably selected a little more than the inner face to mirror - maybe one of the radial lines.


#11

Very cool! nice solution! Thanks again for all your help!


#12

When I look at the GIF again, I can see it isn’t scaling quite about the centre (centre scaling red dot isn’t on the origin). I picked up a stray internal radial line by mistake inside the original shell when scaling - so it isn’t quite symmetrical.


#13

Is there a chance I could get you to GIF the first set of instructions as well? I cant get it create the faces after I add the lines but I am thinking it is just user error. :confused:


#14

Yes, I can do that.

Do you need it urgently? If not, I’d rather do it tomorrow, but could do it tonight if you need it sooner.


#15

What did you mean by ‘shared the same side walls’?

Were they separate from the panels, and with thickness of their own?


#16

Not at all. Whenever you get around to it is completely ok.


#17

Tomorrow then. It’s 10:30 pm here in UK.


#18

They were not separate.

I just meant that the panels shared the same face and thought that once printed, the panels would be a little larger than expected and that the 3 inch ball might be a tiny bit too small once all 12 panels are placed on its surface. I suppose the only way to really test this is to print and see what happens which I am completely ok with.


#19

A bit of sandpapering might be enough if the difference is small


#20

Here’s a GIF of cutting out the elements to make a panel.

I started (but haven’t shown in the GIF) by getting your model the right way up - blue axis up - as I had found myself confused first time round that my panel wasn’t where I expected it to be!

And I only went as far as fixing one edge face - it is easier to do that after turning Xray mode off. Do the others just the same.

Anyway, see if this helps.

You’ll see that I had selected some extra loose geometry with my window select, which I erased before fixing the edges. [And I notice when reviewing the GIF, I erased the point at origin by mistake - you probably want to put that back or deselect it before erasing the other loose geometry].

After fixing the first edge, go round all five edges, reverse faces to get the edge faces facing out, then make a component of the panel and its centre point.

To make it easier for you to follow what I did, I used the menus or toolbars for selections and tool choice. Normally I’d use keyboard shortcuts for all of that - built-in shortcuts {spacebar} for Select tool, L for Line tool, Option (Mac) or Ctrl + X for Cut, Ctrl+A for Select All, Backspace or Delete key for Erase and a custom shortcut Ctrl + V for Paste in place.

Anyway, I hope this helps you.