I thougt this was the question.
“Looking for some brilliant ideas on how to go about carving a 3 foot foam sphere.”
and carving is in my opinion with a machine
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As above. The question was how to make a foam sphere. From what I’m seeing here, there are very few actual ways to do that purely with the CNC, which means they’re using other tools as well. To limit responses to only CNC would be slightly odd limitation, in my opinion.
I frequently find that the best (for whatever criteria I’m using at the time) way to do something is in fact to not just use the CNC. Maybe it’s to use the CNC machine to make a template. Maybe it’s to make something with conventional tools and then finish it with the CNC, or make an inlay.
If your goal is to make things purely or primarily on a CNC machine then have at it, good luck and I wish you well. Personally, I don’t like to confuse that with the goal of making things while having a CNC, as I find that’s typically a more reasonable perspective.
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I’ve been thinking if it’s possible to bend a TIG welding wire (don’t know if that is the correct name) i n a curve and electrically heating it. Then put a block of styrofoam under it with a turning point under the highest point of the curve, then you an turn it and get a sphere:
A quick drawing:
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I plan to have two spheres total, but two different size. the second would be about 2’. So a similar process would be used.
I was thinking of using XPS foam from the big box store.
Let’s assume I use the ring method, I’d make the rings 2-3" wide by however thick the foam is.
There is not specific thickness needed other than not wanting to waste material but need it sturdy.
this reminded me of how stone spheres are ground.
Wonder if I have a rough cut the sphere with layers then make a wood ring with something like a band saw blades attached (sort of a circular rasp). then I could roughly smooth out the steps from layering by moving it around the sphere and then follow up with hand sanding?
Sorry, the video is not playing on my end so can’t see what you are showing.
inside is not important other than it needs to be hollow. I will be placing some components inside.
Printing a mold would be pretty large and costly I think. At least for me.
As jono mentioned it does not need to be CNC, which is why I put it in the Random Off Topic section.
I haven’t completely thrown this idea out yet. I’ve though of it before too. I keep thinking it’d be tough to keep the wire stable as it goes through the foam.
Just ran across this.
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That’s odd. Here’s a different one:
Have a look for the Izzy Swan videos on his ball turning router jig, if you’re interested. That’s what that video is. It’s basically just 2 right angle brackets to make 2 vertical faces. One bracket is fixed in place and has a bolt that rotates in a hole in one of the vertical faces turning a piece of wood to act as a ‘chuck’. The other bracket has a part sticking out the ‘front’ that gets pinned so it can swivel around a point that’s under the face of the chuck piece and then it has a router mounted to it so that the bit sticks out towards the chuck. To use it, the stock gets rotated slowly using the bolt head and the router is advanced by swinging it around the pinned point at the front. Once a full pass has been taken the router can be moved closer, either by changing the height of the router in the base, moving the hole for the pin or moving where the pin is.
For foam, I’d probably just move the router in by hand until it was close and then only pin it in place for the final few passes. It’d depend on how you make the blank a bit, though, I think.
Yeah, that wouldn’t make sense for a one-time use, but if you wanted ~10 or something, the spray foam might be cheaper than the ~30 sheets of XPS or something! 
You could also potentially do it with something like a metal pipe (steel brake line?) or some ~1-2mm flat bar or something like that? It’d be a bit more challenging to heat but it’d hold its shape well. I suspect it’d be too hard to heat electrically but with a blowtorch it’d go. You could CNC cut a 1/4 circle to bend/hammer/press it into shape over.
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this is totally doable.
I could build an A frame sort of thing with conduit running through the foam buck for the sphere.
space the router right on a fixed pivot.
Hmmmm. I’m liking this idea.
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It worked amazingly well for the wooden domes I’ve made before. The nice thing is it also gives you an easy way to sand/finish them because it’s still on the rotary tool.
My thinking is that the challenge is likely getting enough adjustment in the router position to easily go from a rough blank to the sphere, but that depends on how you’re making the blank in the first place. From 2" thick foam pieces cut either by CNC or jigsaw/hand saw/hotwire I suspect you’d end up pretty close, though.
I was thinking you’d also need to make it solid and then hollow it out afterwards, but if you made the chuck face big enough that you could mount the hollow ring directly onto it then you could make it hollow to begin with, which might save you some material if you stacked it up from rings.
I kinda wanna make one now. Sounds fun.
absolutely.
The top and bottom of the sphere need to be opened as well. I can just put a flat temporary “cap” on both and use that to mount it. Maybe wood cap for stability.
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That seems like it’d work quite well. You could start with just a plywood round, mount it to cut the half sphere, cut the center out afterwards and you’re away. That way the foam could just be glued to the plywood straight up without needing to be cut off after…
The plywood round could be oversized and cut at the same time as the rest of the sphere, giving you perfect registration between them, too.
The idea of the stacked foam rings is a good one! To sculpt the sphere, a circular cardboard template can help to check the shape. A milling machine on a swivel arm could also give a more precise result. Otherwise, a sander with a template can work. It all depends on the level of precision sought!
Yep, that is something I need to work trough for the final project.
the ideas on this thread has helped a lot.
Thanks everyone.
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