MIL-D-22233D
External surfaces of the rod shall be carburized to a case depth of not less
than 0.045 inch but not more than 0.065 inch. Internal surfaces shall be
carburized to a depth of not less than 0.035 inch. Rod shall have a case
hardness between Rockwell hardness (Rh) 58C and Rh 65C. The manufacturer's
standard means for maintaining thread lubrication shall be provided.
3.4 Type II - Coupling. Coupling dimensions shall be 2-3/16 inches
±1/16 inch in od by 7 inches ±1/16 inch in length. Internal threads conforming
to figure 3 shall be mismatched at the coupling's center to stop rod movement
through coupling. Mismatched threads shall not interfere with or prevent the
ends of rods from butting against each other when coupled. Coupling shall have
a case hardness between Rh 52C and Rh 58C.
3.5 Type III - shank. Shank shall be style A or B as specified herein.
Style A shank shall conform to figure 1. Style B shank shall conform to figure
2. Shank material shall be alloy steel with the necessary properties required
for toughness, hardness, hardenability, and shock resistance. All machined
surfaces shall be finished to 125 microns. Figure dimensions are in inches.
Unless otherwise specified, tolerances shall be: Fractional ±1/32 inch, decimal
±0.005, angular ±1 degree. The shank ends shall be square with the thread
within 0.005 inch, the thread shall be turned at 90 degrees to centerline of
piece, and all diameters shall be concentric within 0.005 inch. The shank end
to be coupled to the drill steel shall be threaded with 1-1/2-inch rope thread
conforming to figure 3. External and internal surfaces shall be carburized to a
case depth of not less than 0.040 inch but not more than 0.080 inch. Shanks
shall have a case hardness between Rh 56C and Rh 63C. The manufacturer's
standard provisions for retaining the flushing tube seal shall be provided for
the style B shank.
3.6 Type IV - rock bit. All bit bodies shall be of alloy steel having a
case hardness of not less than Rh 42C. The face of style C bits shall have a
case hardness of not less than Rh 36C. Brazing material used to secure the
tungsten carbide inserts to the body of the bits shall be 40 to 50 percent
silver-bearing alloy or not less than 40 percent copper alloy. Bonding
characteristics of the copper alloy shall be not less than those of the
silver-bearing alloy.
3.6.1 Style A bit. Style A bit shall conform to MS 39330, except the
tungsten carbide inserts shall be positioned on the face of the bit to form a
cross configuration.
3.6.2
Style B bit.
Style B bit shall conform to MS39330.
3.6.3 Style C bit. Style C bit shall conform to MS39335. The bit shall be
capable of drilling through 600 feet of Barre granite before destruction.
3.7 Type V - extractor. Extractor shall have the capability to score and
grip broken carburized drill rods and couplings for the purpose of withdrawing
a broken drill string from a hole. Internal threads, at the drill rod end,
shall conform to figure 3. Internal threads, at the extractor end, shall be of
the manufacturer's design.
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