Reversible casing for a down-the-hole percussive apparatus

A casing for a down-the-hole drill, said casing adapted to be connected at a first casing end to operative elements of a drill backhead and at a second casing end to operative elements of a drill fronthead, said casing being capable of being reversed lengthwise when one end thereof becomes abraded during use, comprising:

• a. an elongated, hollow tubular body extending in a lengthwise direction between said first casing end and said second casing end;
• b. an internal surface on said body forming a bore having a diameter D, said bore having an axis extending in said lengthwise direction;
• c. snap ring groove means in said internal surface for retaining therein a snap ring adapted for supporting operative drill backhead elements within said bore, said snap ring having a snap ring aspect ratio between 1.0 and 6.0, said snap ring groove means being substantially centered between said first and second casing ends, said snap ring groove means extending in a radial direction from said axis of said bore, as viewed in a plane transverse to said lengthwise direction of said body, said snap ring groove means having:
• i. a length L, as measured in said lengthwise direction;
• ii. a depth t, as measured in said radial direction;
• and
• iii. a shoulder ratio D/t, said length L having a maximum in the following ranges:
• ______________________________________ Range of Range of Max. Range of Range of Snap Ring Groove Length, Bore Diameter, Shoulder Aspect Ratio, L, (inches) D, (inches) Ratio, r = D/t k = l/t ______________________________________ 0.25-7.80 2.0-10.0 10.0-150.0 1.0-6.0 ______________________________________
• whereby a snap ring will be restrained by said snap ring groove means from skewing out of said snap ring groove when casing is not connected to operative elements of said drill;
• and
• d. said bore internal surface having a profile that is substantially a mirror image, as measured on either side of said snap ring groove means.

A method for producing a reversible casing for a down-the-hole drill, said casing being capable of being reversed lengthwise when one end thereof becomes abraded during use, comprising:

• a. providing an elongated hollow tubular casing having a first casing end and a second casing end;
• b. providing a bore formed by an internal surface therein;
• c. providing a snap ring groove in said internal surface for retaining therein a snap ring adapted for supporting operative drill backhead elements within said bore, said snap ring having a snap ring aspect ratio between 1.0 and 6.0, said snap ring groove being substantially centered between said first and second casing ends, said snap ring groove extending in a radial direction from said axis of said bore, as viewed in a plane transverse to said lengthwise direction of said body, said snap ring groove having:
• i. a length L, as measured in said lengthwise direction;
• ii. a depth t, as measured in said radial direction;
• and
• iii. a shoulder ratio D/t, said length L having a maximum in the following ranges:
• ______________________________________ Range of Range of Max. Range of Range of Snap Ring Groove Length, Bore Diameter, Shoulder Aspect Ratio, L, (inches) D, (inches) Ratio, r = D/t k = l/t ______________________________________ 0.25-7.80 2.0-10.0 10.0-150.0 1.0-6.0 ______________________________________
• whereby a snap ring will be restrained by said snap ring groove from skewing out of said snap ring groove when casing is not connected to operative elements of said drill;
• d. providing a first groove means in said internal surface between said snap ring groove and said first casing end, for supporting operative elements of a drill backhead in said bore and for defining, with said operative elements of a drill backhead, passageways for flow of percussive fluid therein, when said first casing end is connected to a drill backhead;
• and
• e. providing a second groove means in said internal surface between said snap ring groove and said second casing end, for supporting operative elements of a drill fronthead in said bore and for defining, with said operative elements of a drill fronthead, passageways for flow of percussive fluid therein, when said second casing end is connected to a drill fronthead.