Cutting Apparatus and Drive Assembly

A boring apparatus according to any preceding claim wherein the primary feed motor is a hydraulic motor operable at a minimum primary feed rotation velocity and at a maximum primary feed rotation velocity wherein the ratio of minimum primary feed rotation velocity to maximum primary velocity rotation velocity is from 1:10 to 1:30.

A boring apparatus according to any preceding claim wherein each planetary gear assembly comprises three or more planetary gears substantially uniformly distributed around the sun gear.

A boring apparatus according to any preceding claim which is a hot-tap drilling apparatus suitable for drilling a hole into a wall of a pressurised pipe, wherein the cutting head comprises a hole saw cutter and pressure-tight seals around the boring bar whereby pressurised contents of said pipe are prevented from escaping the pipe and/or entering other components of the hot-tap drilling apparatus.

A method for controlling axial movement of the cutting head of a boring apparatus according to any preceding claim whilst the cutting head is rotating at a cutting rotation velocity ω1, the method comprising:

• operating the primary feed drive motor to drive the primary feed drive shaft at rotation velocity ω2 with the ring gear of the other or secondary feed planetary gear drive held with rotation velocity zero,
• whereby the feed screw is driven through the first and second planetary gear assemblies at a rotation velocity (ω1+k·ω2) wherein k is a gear ratio. whereby the relative rotational velocity between the feed screw and the feed nut of the boring bar is k·ω2, causing the boring bar to move axially along the feed screw at a rate P·k·ω2.