nearly eliminated drill body displacement. In all cases, the cycle repeatability in terms of 

 magnitude and repetition of impacts improved with an increase in applied downward force. 

 Figure 8 shows drill body displacement reductions for several values of added force. 



Reductions to Plunger and Piston 



From a practical standpoint, a 150-pound or more rock drill was not an acceptable 

 solution. What was desired was an optimized impact mechanism for the 50-pound drill weight. 

 Viewed as an energy balance problem, improvement was expected through a scaled reduction of 

 the plunger and piston size. The energy used to drive the scaled plunger and piston produced 

 less reaction force to displace the rock drill body. 



Table 1 shows a comparison of several parameters used in the baseline 3P drill with those 

 tested as part of the validation of the reduced plunger and piston areas. Drawings of the 

 redesigned plunger, plunger sleeve, sleeve cap, and piston are provided in Appendix B. 



Of several model runs at various values of plunger and piston areas, the best results were 

 produced with a plunger area reduction of 30 percent and a piston return area reduction of 36 

 percent. The ratio of plunger area to piston return area has a measurable effect on cycle timing. 

 Some slowing of the cycle was desired to preserve timing functions. This necessitated the 6 

 percent greater reduction in piston return area. Further investigation into timing effects revealed 

 that by opening the kicker port to the exhaust port sooner (i.e., move the kicker port closer to 

 the exhaust port in the plunger sleeve), the amount of external applied force could be reduced 

 to 100 pounds. 



Table 1 

 Comparison of Evaluated Design Parameters 



Parameter 



Baseline Production Drill 



Redesign Validation 



Operating Pressure 



1,500 psi 



Tested at 600, 1,000, and 

 1,500 psi 



Added Weight 







Tested at and 100 lb 



Plunger Head Diameter/ 

 Area 



0.555 in. 

 0.24 in. 2 



0.466 in. 

 0.17 in. 2 



End Cap on Plunger 



Yes 



No, single diameter 



Plunger Stop (lower) 



Sleeve 



Piston 



Plunger Length 



3.687 in. 



3.996 in. 



Piston Return Area 



9 



0.0807 in. 2 



0.0514 in. 2 



Groove in Poppet 



Yes 



No 



Piston Stop (upper) 



Housing 



0.31 in. down 



