Laser machining has emerged as enabling technology that holds immense potential for advancing the miniaturization across various industries. With the rapid advancement of laser technologies, the boundaries of what is attainable in the miniaturization have expanded significantly. In this paper 3D direct laser ablation of microchannels in glass for microfluidic and medical applications is reported. Process understanding and optimization plays a decisive role in achieving controlled volumetric material removal with specified surface roughness. By harnessing adequate combination of machining parameters, a trade-off between surface roughness and ablation rate is achieved to ensure the required quality, reproducibility, and process reliability.