Shaft internal lubrication with rifling grooves

1. A shaft internal lubrication system comprising:

a shaft body having an outer wall and a central bore defining an inner wall;

a plurality of lubrication holes axially distributed along the central bore and fluidically connecting the inner wall and the outer wall;

at least one rifling groove on the inner wall, the at least one rifling groove forming a lubrication flow path to two or more of the lubrication holes; and

a feed tube within the central bore operable to drip feed a lubricant to the inner wall.

2. The system of claim 1 , wherein the at least one rifling groove comprises two or more riffling grooves, and each of the two or more riffling grooves contacts a different subset of the lubrication holes.

3. The system of claim 1 , wherein the lubrication holes provide splash lubrication to a plurality of components coupled or proximate to the shaft body.

4. The system of claim 1 , wherein the feed tube is configured to receive the lubricant from an excess lubricant supply collected in a passage formed substantially perpendicular to an axis of rotation of the shaft body.

5. The system of claim 4 , further comprising a scupper configured to collect the lubricant splashed upon exiting the shaft body, wherein the scupper is in fluid communication with the passage to provide the lubricant collected.

6. The system of claim 4 , wherein the passage is a vertical column in a gearbox housing, and the lubrication flow path within the central bore is a substantially horizontally oriented spiral configured to urge the lubricant toward a driven end of the shaft body.

7. The system of claim 1 , wherein the at least one rifling groove is configured to urge the lubricant longitudinally through the central bore due to centrifugal forces.

8. A reduction gearbox of a core-turning system for a gas turbine engine, the reduction gearbox comprising:

a reduction gear train operable to drive rotation of a starter gear train of the gas turbine engine, the reduction gear train comprising a plurality of gear systems driven by a shaft having a shaft internal lubrication system comprising:

a shaft body having an outer wall and a central bore defining an inner wall;

a plurality of lubrication holes axially distributed along the central bore and fluidically connecting the inner wall and the outer wall; and

at least one rifling groove on the inner wall, the at least one rifling groove forming a lubrication flow path to two or more of the lubrication holes; and

a mounting pad comprising an interface to couple a core-turning motor to the reduction gear train.

9. The reduction gearbox of claim 8 , wherein the at least one rifling groove comprises two or more riffling grooves, and each of the two or more riffling grooves contacts a different subset of the lubrication holes.

10. The reduction gearbox of claim 8 , wherein the lubrication holes provide splash lubrication to the gear systems driven by the shaft.

11. The reduction gearbox of claim 8 , further comprising a feed tube within the central bore operable to drip feed a lubricant to the at least one rifling groove, wherein the feed tube is configured to receive the lubricant from an excess lubricant supply collected in a passage of a housing of the reduction gearbox.

12. The reduction gearbox of claim 11 , further comprising a scupper configured to collect the lubricant splashed upon exiting the shaft body, wherein the scupper is in fluid communication with the passage to provide the lubricant collected.

13. The reduction gearbox of claim 11 , wherein the passage is a vertical column, and the lubrication flow path within the central bore is a substantially horizontally oriented spiral configured to urge the lubricant toward a driven end of the shaft body.