Advice on cnc design dual feedback control

Hello to everyone in the forum.

Thank you all for sharing all your insights it is very helpful.

My son (a designer and developer) and I (engineering background) started a project to build a CNC router capable of manufacturing non-Ferro materials with a wide as possible product envelope, within the (well known) optimal balanced performance, prize and quality triangle constraints.

The project is in its final design phase using CAD to define the details such as length of the structural elements: 30x30mm aluminium extrusions, aluminum front and back plate length, brackets, etc.

Some products have been ordered to narrow the design choices leading towards the final detailed design.

This design is based on the following assumptions:
1. 2x X-axis, 1100mm leadscrew kit with SFU1605 Ball nut (C7) (effective 1000mm)
 2x SBR16-L1100mm & 4PCS SBR16UU per axis

2. Y-axis, 1100mm leadscrew kit with SFU1605 Ball nut (C7) (effective 1000mm)
 2x SBR16-L1100mm & 4PCS SBR16UU

3. Z-axis, 400mm leadscrew kit with SFU1605 Ball nut (C7) (effective~ 300mm)
 2x SBR16-L1100mm & 4PCS SBR16UU

4. 4x Nema 34 Stepper Motor (34HS5435C-37B2) of 1600oz-in & flexible Jaw Coupler

5. 4x Stepper Driver DM860A with individual power supply

6. 8x Inductive 4mm Proximity Sensors on the axis (LJ12A3-4-Z/BX)

7. 1.5KW Water Cooled Spindle Motor ER16 kit

8. 14x 30x30mm aluminium extrusions

9. 2x 1100x150x10mm aluminum (6060) support plates

10. ~1100x1100x500mm steel-welded support table

11. Dedicated computer system
a. Motherboard: Z87-Plus, i5 4690 / 3.5 Ghz - 6 MB cache
b. Memory: 16 GB DDR3 OS
c. Storage: 128 GB SSD and 1 Tb HD
d. OS: Ubuntu 14LTS with of course LinuxCNC

12. EMC mitigation by shielded cables matching the max. power demand

13. Linear scale encoders on all three axes ~ 1000x1000x400mm

Some questions arose during the design process which I would appreciate your judgement on:
1. Is this a feasible design setup, why or why not? What must be changed?

2. What (open loop) accuracy could be expected on the machine? My calculation resulted in about 450 µm.

3. I’m interested in adding linear scale and rotary encoders to the setup:
www.aliexpress.com/item/3-AXIS-DIGITAL-R...rue&isOrigTitle=true

3.1. Are these in the 1 micron scale suitable?
3.2. Are 2 linear encoders for the X axis recommended, since we'll be using 2 motors on the X-axis?
3.3. If these aren't suitable, are there other recommendation?
3.4. Are there recommendations for rotary encoders?
3.5 Can the rotary encoders be connected to the end of the leadscrews opposite of the motors?

4. What is the expected frequency on the motor wiring system?

5. Must the 4 motor wires be twisted and shielded individually up to the DM860A?

6. Is an isolation transformer recommended?

Thanks a bunch,

Harry and Marco

You may want to post a picture of what this machine looks like, but I can tell you those stepper motors and ballscrews have no business together.

I could see much smaller motors with a 5mm pitch screw. Or those 1600oz-in nema34's with a much lower pitch (yet with less resolution)
If you use what you listed, you will have something like 750 mm/min (30 inch per minute) max travel speed. (don't know what power supply voltage you will run, maybe twice that with 80V input)
Very slow for a router.

Don't bother with encoders if you are using stepper motors. You will have 0.025 mm resolution, but your ballscrews are only accurate to 0.05mm per 300mm (if they are actually C7 spec)

Also rethink using the round linear bearings. Profile rails are not much more expensive, yet much more rigid.

I think first you need to figure out what your maximum required force is, and also maximum travel speed.

It is very easy to build a machine with budget as the first consideration, and find you have a machine that dissappoints you.