The investigation collected some useful information, but I believe it fell short of exploring significantly novel findings. The geometry of the bit remained within existing design and ice properties were neglected. The setup should have been used to explore beyond the range of what is currently used in ice drills to expand into novel territory and give evidence to drive changes to current technology.

• The most interesting finding to me was seen in Figure 9 and discussed in lines 246 to 254; the low frequency oscillations from the formation and clearing of ice chips. I would like to see this concept expended – inherently all ice drills deflect under load so is it possible the oscillating cutting force creates a harmonic in the drill? Does this effect core quality? Can the oscillation be mitigated? Or could the drill be tuned to minimize cutting power by harnessing the momentum created with the ice fractures?
• I would like to see the effect of ice properties explored against the cutting force. We know that the ice properties change significantly with grain size and temperature (Petrovic, J.J., 2003) but this was not included in the study, although a robust drill design must work in a variety of conditions.
• The range of rake angle was from 20° to 40°, which doesn’t even include the range of existing drills. Plots, such as Figure 10, indicated that the cutting force will continue to decrease with increasing rake angle. I would have liked to see that explored, at least until a physical limit was approached (e.g. the rake angle intersected with the relief angle). Then future designers could pursue better blade design and weight it against durability.
• Same with depth of cut – it would be useful continue the trend to a maximum or asymptote.

Overall, I would like to see the paper discuss a novel finding. The range of variables could be expanded, so the data enters new territory that has not already been proven with drills in operation. Alternatively, a discovery such as the force oscillation could be the focus. To my knowledge, this is a new finding that has not been published in connection with ice drilling. 

Petrovic, J.J., 2003. Review mechanical properties of ice and snow. Journal of materials science, 38, pp.1-6.

This paper investigates a few basic variables that influence ice cutting force, but the experiment lacks focus to develop a novel understanding of ice cutting mechanics. Differences in ice properties are briefly mentioned in the introduction, but not discussed further in the context of study.  The range of experimental parameters was limited and is not representative of typical ice coring equipment deployed in polar regions. Evidence for brittle fracture is shown with the high-speed camera for one set of parameters, but there is no discussion on how cutting depth or rake angle could influence failure mode.

Specific comments follow:

• How were the cutters sharpened for this study? Was the rake surface polished? I expect cutter sharpness and rake surface finish to impact cutting performance and cutting force.
• I would like to see a wider range of rake angles investigated that include existing drills. Negative rake angles are not discussed in this paper but could provide an interesting comparison.
• I would like to see a more detailed analysis of how the ice fracture mechanics change with depth of cut. High speed imagery is only provided for one set of parameters. At a minimum, I would like to see a comparison of imagery between different depths of cut.
• The force diagrams in Figure 7. does not account for the presence of a cutter shoe which limits depth of cut. During cutting, I expect F_p to shrink to zero once the shoes are fully contacting the bottom of the borehole behind the cutter.
• I would like to see a comparison of the cutting force trace (Figure 9) for different depths of cut. It would be interesting to compare the resulting frequency as chip size changes.

I would like to see this study revisited to focus on developing a novel understanding of ice cutting mechanics. Focusing on force oscillation or how cutting mechanics vary with depth of cut could yield a novel finding.