An abrasive waterjet milling technique has been developed to machine brittle amorphous glass in a controlled-depth milling mode, without using sacrificed masking plates made of hard materials. The main mechanisms associated with the milled channel formation process, i.e. the particle impact erosion, jet flow characteristics and the dynamics of nozzle motion, are analysed to arrive at the models for predicting the material removal rate and the geometry of the channels milled by this technique. It is found that these milling performance quantities are dominated by nine dimensionless variables representing the processing parameters and material properties that govern the major mechanisms involved in the milled channel formation. An experimental verification has been carried out and shows that the model predictions are in good agreement with the corresponding experimental data.