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.
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.
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.
One main reason professional 5 axis CNC machines are so expensive is because they are very rigid yet can move quickly and precisely.
[0]http://millingaccessories.biz/2015/04/07/maxnc-10-cnc-millin... [1]https://lh3.googleusercontent.com/-TkXnpUUXqLg/T4Qj3qVU9JI/A...
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.