US 4,053,249 AGranted

Apparatus and method for precision overboring an arcuate, variable diameter bore

AssigneeGeneral Electric Company

InventorsPhillip D. Ness, Robert A. Long

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Abstract

An apparatus and method for precision overboring a variable diameter existing bore through a metal shaft supported in a position that causes the shaft to sag along its longitudinal axis. A plurality of precision-formed tool pilots are selectively mounted ahead of a spade bit on a rotary boring tool to maintain the path of the bit through the shaft-workpiece within a predetermined tolerance of the path followed by an existing bore. A plurality of fluted follower bearings are positioned around the tool driving shaft to minimize its vibration as the bit proceeds through the workpiece. Liquid coolant is passed at high volume into engagement with the bit and thence through the follower bearing exhaust passageways to flush metal shavings and chips from the overbore. According to the method of the invention, tool vibration is carefully monitored as the bit is forced into the workpiece. Responsive to detection of a predetermined degree of tool vibration, the pilots are selectively changed to maintain on the boring tool a pilot having a guide surface diameter within said predetermined tolerance of the various portions of the existing bore through the workpiece sequentially closest to the spade bit, as the pilot passes each such portion.

Claims10

Dependent claims

Apparatus for precision overboring a variable diameter existing bore along the longitudinal center axis of a metal shaft supported in a position that causes the shaft to sag along the longitudinal axis of said existing bore, comprising, a rotary boring tool including a boring end and having a drive shaft at least as long as said existing bore, said drive shaft including wall means defining a multiple-outlet passageway for conducting coolant to the boring end of the tool, a double-bladed spade bit operably mounted on the boring end of the tool, said bit having a fixed cutting diameter substantially larger than the maximum diameter of said drive shaft, one of a plurality of boring tool pilots operably mounted as the leading end of the boring tool immediately ahead of said bit, each said pilot having a precision-formed cylindrical guide surface that matches within a predetermined negative tolerance to one of the respective diameters of the existing bore through the metal shaft upon which the apparatus is to operate, each of said pilots being selectively mountable in operating position on the boring end of the rotary tool ahead of the bit, with the particular pilot having a guide surface matching within said predetermined negative tolerance the respective diameter of the existing bore of the metal shaft upon which the apparatus is to operate immediately ahead of said bit, and a plurality of follower bearings having precision formed generally cylindrical outer surfaces the outer diameter of which follower bearing matches within a given negative tolerance the maximum fixed cutting diameter of said bit, each follower bearing including a first wall means defining an aperture through the center thereof that enables the bearing to slide snugly over the boring tool drive shaft for rotation therewith and including a second wall means defining a plurality of exhaust apertures extending longitudinally through the bearing for conducting coolant and metal shavings rapidly away from the bit and out of the overbore, said follower bearings being positioned respectively around the tool drive shaft at longitudinally spaced points thereon.

A method for precision overboring a variable diameter existing bore along the longitudinal center axis of a metal shaft supported in a position wherein the shaft sags along the longitudinal axis of said existing bore, comprising the steps of:

a. providing a rotary boring tool having a drive shaft at least as long as said existing bore and having a coolant passageway extending through the length thereof, and providing drive means operatively connected to said tool for driving it through said existing bore,
b. providing a source of liquid coolant and flow control means for selectively forcing coolant through said passageway,
c. mounting a double-bladed spade bit in operative position on the boring end of said tool, said bit having a fixed cutting diameter substantially larger than said existing bore diameter,
d. providing a plurality of boring tool pilots each having a different diameter, precision-formed, cylindrical guide surface that matches within a predetermined tolerance one of the respective diameters of said existing bore, and mounting on said tool ahead of the bit one of said pilots matched to within said predetermined tolerance of the diameter of said existing bore at one end thereof,
e. operating said drive means to drive the pilot through said one end of the existing bore and to cause the bit to cut an overbore the longitudinal axis of which is caused by said pilot to match the longitudinal axis of the existing bore within said predetermined tolerance,
f. operating said flow control means to cool said bit and to rapidly flush metal chips out of the overbore,
g. monitoring the vibration of said rotary tool as the bit is driven through the shaft, thereby to detect a degree of vibration indicative of said predetermined tolerance being exceeded, and responsive to an indication of such excessive vibration changing the pilot initially mounted on said tool for another pilot having a guiding surface diameter within said predetermined tolerance of the portion of said existing bore then closest to the bit,
h. continuing the overboring by repeating steps (e) and (f) and then repeating step (g) to successively substitute different diameter pilots as indicated by the detection of excessive tool vibration until the overbore is completed,
i. providing a plurality of generally cylindrical follower bearings each having a plurality of coolant exhaust passages extending longitudinally therethrough, and each having a maximum outer diameter that matches the maximum cutting diameter of said bit within said pedetermind tolerance, and
j. mounting said follower bearings at spaced points on said drive shaft prior to the movement of said spaced points into the overbore as the operations of step (h) are continued.

7 more elements

Dependencies are inferred from the claim text.