Desktop sized CNC

[JAZZCNC]

As for rails, I think to use MGN12 rails with MGN12H carriages for Z and X axis. For Y axis HGR15 with HGW15CA (or other type, depending on final design) carriages.

I have concerns if MGN12 with MGN12H will be enough for Z and X axis ? (even though I have seen those used in small cnc machines).

You will be better with HGR15 or better still HGR20. The bearings are easier to work with and not so tiny.

I really liked the CSMIO/IP-M 4-axis Ethernet Motion Controller, but in specs it shows that the spindle axis is not supported ?

No this means you can't control the spindle has an Axis like you would if using Servo Motor with Encoder, say for Spindle orientation with ATC or ridged tapping. But it does have 0-10v Speed control with Relay Output for On/Off.

As for stepper drives, I will go with DM556 (or if needed - AM882). But what about steppers ? What torque I would need? (I plan to use pulleys and make 2:1 gearing or just leave it 1:1). The size is important too - smaller steppers are better for my design :)

Well difficult to say exactly without knowing Mass etc but like Lee says 3.1nm will give good balance of power and speed so often used. More important is that you choose Steppers with Low inductance to give good torque at speed.

Do I need closed loop steppers and drivers ? are they worth the money[/URL] ? )

No you don't need them and provided you match the electronics correctly and don't overtune motors you won't lose steps.

But if you can afford them then there are some advantages other than the closed Loop.? . . Three phase motors are much smoother and give more torque across the speed curve. They also handle resonance much better.

Thou I'm not sure about those Drives/motors has I've never used them and not all Closedloop are the same. You'll also need at least 2Nm, ideally 3nm.