Nice website!
Yeah both humans and multiaxis cnc machines can articulate their arm to apply a tool to a work piece and both a sparrow and an F16 can fly through the air.
A sparrow can take off and land on a branch, and it regularly weaves through thick foliage no wider than its wingspan. So, I assume the human is the sparrow?
Optical tracking might be easier.
I'm not sure how much deflection you could actually tolerate before deforming the joints in the arm. Even with deflection tracking you might end up taking very, very shallow cuts. A 3D printer that runs for 16 hours in your apartment is annoying, a CNC mill running for 16 hours will be genuinely intolerable.
No. There's no substitute for rigidity in fixturing and of the machine itself. There will also be vibration motions that have unpredictable nodes, frequencies, and amplitudes.
Consider that a 2 flute mill at 20,000 rpm will induce vibrations with a fundamental frequency of about 670 hz. This would require a servo system with a bandwidth of about 2 khz to correct, a sampling rate of 8khz would be a bare minimum.
Next, what to do if the tool digs in, and shoves the part? You have to have backlash sufficiently damped, and rigidity enough to keep the tool or part from being snapped off.
There's a good reason machine tools are as heavy and rigid as they are, and why they must be on a thick foundation, and leveled precisely before use.
If you're going high precision, you'll also have everything in a temperature controlled environment, and allow the materials to soak at a day to achieve the proper temperature. Cooling is very important when you get into fractions of a millimeter, or "tenths" (1/10,000 inch) tolerances.
The best machine tools are old American cast iron machines from about 1940 to 1960, rebuilt with modern control systems.
The only issue I have with this design is that the accuracy decreases with the distance from the rotary axis, hence it is not uniform over the building volume.
3d printers don't have forces pushing back on the print head, nor the vibration from a cutting tool to deal with.
This design might work ok for 3d printing, or laser cutting, or anything else where no contact between the working head and the material occurs.
As far as accuracy and repeatability, it's going to be about as good as the average 3d printer design. It's a nifty idea for a system, but it's only a decent machine for cutting if it's scaled up massively and built of cast iron or similar materials.
Either open loop (ie. use mechanical models to predict frame flexing and compensate for them), or closed loop (have sensors to detect realtime head position).
The whole idea of having a frame which is 100% rigid seems like a simplifying assumption that makes everything more expensive, with knock on effects too (eg. making stuff stronger makes them heavier, which in turn means a bigger motor is needed, which uses more power, so a bigger power supply is needed, etc)
Even then, compensating for sudden release in tension, where the tool tries to spring back, seems perhaps insurmountable.
Then you can use that to apply large brief forces in whatever direction is needed to stop chatter for a few milliseconds with each turn of the cutting tool.
It's the same mechanism used in iphones "taptic engines" to make 'clicks'.
The same mechanism can be used to actuate the head at far higher frequencies, allowing cutting fine detail at high speeds.
If a lighter frame was the design goal (but low cost wasn't!) then carbon fiber has an interesting stiffness/weight ratio and could have viscoelastic damping elements incorporated too. Realistically though, lightness isn't a prioritized design goal though I certainly see the appeal in marketing for home usage where you wouldn't need a crane to move the machine about.
I played with a wood router CNC in high school and loved it. I've also played around with 3D printers a bit. The idea of having (and building?) a reasonable system that can do both strong appeals to me.
it is built with that modularity in mind but as other commenters have pointed out building something for rigidity makes it slower and heavier. a cheap 3d printer like an Ender 3 in addition to the MPCNC makes more sense, especially since you can save on the MPCNC by 3D printing the components yourself.
The main benefit to swapping a 3d printer head onto the MPCNC would be the pretty massive XY size you can build the MPCNC out to. If you need to print really large, flat objects it is probably cheaper than a lot of alternatives. But at that point it probably would make more sense just to mill it out of wood anyway.
What's the risk from this? That CNC work will be affected by resistance from materials, causing the frame to bend? What kind of scales would that effect be noticeable on?
You will not be doing any real cutting on this machine.
Also, with a vertical spindle and CNC control, there is no reason to have a vertical rotary axis. The reduced motion doesn't buy any capability upgrade. The 4th axis that is helpful would be angular. (you could put a horizontal spindle on this, I guess, but this machine is not up to the task.
The extent it will be inaccurate depends on a lot of factors, such as tool length, material parameters, feeds/speeds, etc. You can probably cut aluminum somewhat accurately on this if you take extremely slow cuts, with a tiny tool spinning at an extremely high RPM (which keeps cutting forces to a minimum). Surface finish would still be pretty bad simply due to vibration of the arm. Likely going to break a lot of tools too. The majority of metal cutting setups you would do on a mill are simply impossible on this machine.
For a few tiny cuts, it might be handy to have one of these, but it definitely seems more useful as a 3D printer, plotter, etc. Though even most 3D printers are significantly more rigid than this design.
I'd probably argue that anything worse than 0.5mm (~20 thou) will start giving you headaches if your making parts that are supposed to interact with each other. That said, if you're making basically oneoffs and are willing to handfit, that tolerance is probably tolerable (ha!).
"Serious" just means the ability to cut more useful materials, like wood or steel.