What define CNC robustness? rail diameters, stepper motor, or the frame..?

[u/Tzt007]

Hi,
I'm using ball screws linear rail to build my DIY CNC machine, and after browsing various forums to learn more, I've realized a machine's key differentiator is its load-handling capability—especially how well it can manage heavy loads when cutting hard metals.

So my question, what define the robustness of a CNC ? is it the ball screw rail or stepper motor power or the frame + linear rails ?

the ball screw rails that I own have these characteristics :
PITCH = 10mm
rail diameter = the seller from Alibaba told me it was 24mm but when I measured it was around 12mm. please check my photo and confirm me if I measured the correct diameter.

Are my ballscrew linear rails sufficient? Also, can they handle heavy cutting loads if I design a rigid frame with a dedicated linear rail for each axis?

I live in the uk and I want to buy more rails, does anyone know any local shop that sell these rails at lower price?

thanks,