Epoxy-granite gantry cnc - Ballscrews with direct or belt drive? (Noise/precision)

[MaxH]

Hi,
Im new here, from Austria and currently planning to "massively" upgrade my cnc-router.
The base will be arround 110x75x10cm with U shaped cutout on the front for the 4th-axis

Currently i have a ground ballscrew 2510 in the center with 1:1 belt drive (limited space) with jmc 400W Servo (3k rpm nominal)

I want to upgrade to two screws (left and right with slave axis) with ground C5 screws from TBI
Unfortunately, space, weight and noise is a concern. (Flat)
Rpm and torque wise it would make more sense to go 5mm pitch (24mm dia) and maybe direct drive.

Im now thinking about the pros and cons of 5mm vs 10mm pitch and direct and belt.
Does anybody have experience when it comes to sound/vibration when changing from 10 to 5 and also from belt to direct?

I have limited tools and will/want to cast the epoxy directly on a~20mm facemilled aluminiumplate

I can add a 3D preview later if its too unclear how its supposed to look.

Greetings and thanks in advance,
Max

[pippin88]

Direct drive is easier but requires larger / more powerful servos compared to belt reduction.

You won't be spinning your ball screws at 3000rpm generally, so much of the operating range of the servo is wasted if you don't hear down.

3:1 gives you 3x the torque but 1/3rd the rpm.

[MaxH]

With 5mm pitch i would actually spin them with up to 3k rpm
My fastfeed is now 10m/min which would is 1krpm for the 10mm pitch one

[pippin88]

How long will the screw be?

You may run into screw whip issues at 3000rpm.

Have you calculated the critical speed of the screw?

[MaxH]

Yes i calculated it and chose 25mm to be safer there, with 20mm it eouldnt be possible. It will be arround max 1100mm but including end-machining.
The other option would be to take 10mm pitch and gear the servo down with belts 2:1
I would then have a max of 1500rpm on the screw.
Noise is really a big concern for me but i never worked with bigger 5mm screws so i cant estimate the impact on sound.
My 10mm screws, if lubricated, free of chips and mounted properly were always quite ok.

Lower pitch = more ball movement/rpm = more sound?

[Neale]

Can't believe that ballscrew noise would ever be a problem. My steppers are noisier than the ballscrews (although servos are quieter) but all that is lost once the spindle starts running - even water-cooled - and cutting noise is loudest of all.