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Re:The Polar Bear – Open-Source, Multipurpose CNC Machine wi... by donquichotte on Thursday August 19, 2021 @05:05AM (#28231777)
Very cool project. I guess actual subtractive manufacturing can only performed on very soft materials like foams - I have an eShapeoko which is stiffer than this construction and the frame starts flexing quite easily.
Re:The Polar Bear – Open-Source, Multipurpose CNC Machine wi... by kadirilkimen on Friday August 20, 2021 @07:41AM (#28244941)
Hi, I made some carving on wood while developing the prototype. But didn't documented it. It is possible to cut wood. But not metal of course. You can get good results with the wood.

I machined plaster and wood on this machine. Both works well. I had only one 775 motor without speed controller while developing the machine. So, if you have a configurable rpm spindle with low vibration, you can get very good results on wood.

It's a 3d printable cnc machine. Of course it is not rock solid rigid and can't machine hard parts precisely.

It is pointless to compare this machine with a high end high precision machine. You can't get that rigidity and precision from a 3d printed part.

But, may be someone wants to build it from metal. Then you may consider to get better results.But this requires more modification because you can't expect high precision while using v-slot wheels.

Re:The Polar Bear – Open-Source, Multipurpose CNC Machine wi... by abdullahkhalids on Thursday August 19, 2021 @05:35AM (#28231918)
What do you mean? Lathes have been used to do subtractive manufacturing with metal for thousands of years. Modern Lathes are CNC types and can build a lot of stuff.

https://en.wikipedia.org/wiki/Lathe

Re:The Polar Bear – Open-Source, Multipurpose CNC Machine wi... by donquichotte on Thursday August 19, 2021 @05:53AM (#28232042)
Rigidity of the frame is key for accurate and safe subtractive manufacturing.

You do not want your frame to flex while a spindle is cutting aluminium at 20kRPM. See Marco Reps and Kris Temmerman on youtube, they built formidable high precision CNC mills out of steel and concrete. For machines that rely on frames made out of extruded aluminium, flexing has always been an issue, even with much sturdier designs such as the Avid CNC machines.

Also, FYI, in a lathe the workpiece spins, and in a mill the tool spins.

Re:The Polar Bear – Open-Source, Multipurpose CNC Machine wi... by sschueller on Thursday August 19, 2021 @05:49AM (#28232007)
This thing is not very rigid and the interconnections are made of plastic. There is a lot of flex and anything other than soft materials can not be milled with any precision.

One main reason professional 5 axis CNC machines are so expensive is because they are very rigid yet can move quickly and precisely.

Re:The Polar Bear – Open-Source, Multipurpose CNC Machine wi... by GravitasFailure on Thursday August 19, 2021 @05:56AM (#28232052)
That cantilever design is known for having rigidity problems for 3D printers and isn't used at all for subtractive manufacturing. Compare it to a MaxNC 10[0] or a Taig[1] micro mill and you'll be able to see how much more robust their construction is.

[0]http://millingaccessories.biz/2015/04/07/maxnc-10-cnc-millin... [1]https://lh3.googleusercontent.com/-TkXnpUUXqLg/T4Qj3qVU9JI/A...

Re:The Polar Bear – Open-Source, Multipurpose CNC Machine wi... by imtringued on Thursday August 19, 2021 @05:53AM (#28232038)
And they were built using solid cast iron. Meanwhile this machine consists of one big aluminum extrusion and a thin extrusion. It's clearly built for speed not rigidity.
Re:The Polar Bear – Open-Source, Multipurpose CNC Machine wi... by Turing_Machine on Thursday August 19, 2021 @12:02PM (#28235531)
> Meanwhile this machine consists of one big aluminum extrusion and a thin extrusion.

With long cantilevers (i.e., supported at only one end) on both, to boot. Long cantilever, thin material = slop.

Even a small bench top lathe has hundreds of pounds of cast iron in the bed and ways, as you said.

That aside, a lot of the jobs they show in the video (pen-plotting, wood-burning, 3d printing, etc.) don't really demand a huge amount of rigidity. I wouldn't want to try any serious milling or turning with this machine, for sure, but for those jobs it looks like a totally reasonable design.

And I do like the fact that it's designed to be 3D printed itself (other than the extrusions and stepper motors, etc.), so well done on that.

Re:The Polar Bear – Open-Source, Multipurpose CNC Machine wi... by erdii on Thursday August 19, 2021 @05:45AM (#28231976)
Lathes are kind'a more rigidly built though and I think that is what GP tries to point out.