Designing a CNC+Printer

[Zondartul]

Hello, 3D Print Board.


I am designing a desktop CNC machine (as a university research topic for the next few months) and would like some advice.


The machine would be primarily a CNC mill (for 3D substractive manufacturing) but also support 3D printing via interchangeable tools. For the budget I'm thinking 500-1000 USD for a finished product, and maybe 3x that for prototyping. The machine would be used for research purposes and to make robot parts. I would like it to cut wood and aluminum.


Do any of you have experience with designing or modifying 3D printers or CNC machines (routers / mills)? I have a masters in electrical engineering but I know precious little about mechanical engineering. I've built a really cheap 3d printer back in the day (kinda like Prusa Mendel i1), but for a project of this magnitude I believe some reading and calculation is necessary.


In particular, I'm worried about the forces involved when cutting wood and aluminum, and how the frame of the machine needs to be extremely rigid to prevent the cutting bit from deflecting so much that it's not actually cutting (and to have any semblence of accuracy).


Example: many DIY CNC mills/routers on YouTube use spindles (motor+shaft+tool holder) rated for 500W, and a napkin calculation tells me that it would give a torque of 0.5 N*m when cutting, which would generate a translational force of 50..150 N depending on endmill size (so like the weight of a half-full 1-gal water bottle for an office cooler... or 2 cats). I'm also considering designs where the tool is stationary (or only moves on one axis) while the workpiece moves on two or three.


Now for my questions:
- What should I use for the spindle and for the linear stages?
- How can I make a printer hot-end attachable in addition to, or instead of, the drill/mill bit?
- What parts should I absolutely not go cheap on?
- How do I calculate the forces involved, the size the mechanical elements, and the precision that can be achieved with the chosen design?
- Are there any free/open-source programs that would allow me to simulate how much the whole thing would bend when a force is applied?
- Are there any university-level books on mechanical engineering I should read?


Thank you for your time.