El contexto (y las referencias adjuntas de, entre otros, Unisig) parecen indicar que la operación es de escariado (término técnico) o ensanche/ampliación (términos más comunes) de perforaciones practicadas previamente con taladro o hechas mediante molde. El término “pilot” puede ser un sustantivo o un verbo. Como sustantivo es el componente o pieza guía, es decir, el piloto de la broca que se emplea en la herramienta con la que se contrataladra (véase ref. de Wikipedia).

Pero en este caso concreto “pilot” es un verbo, sin duda. Puede traducirse como “operar” o “guiarse” (la máquina se guía o desplaza desde…). Y según lo interpreto yo “off” sería una preposición espacial que indicaría el lugar desde el que se practicaría la ampliación de la perforación inicial (para conseguir el diámetro o la concentricidad requeridos).

HTH

http://www.americanheller.com/counterboring-sts1-indexable.h...
If bore straightness is critical to your part processing and you do not wish to make modifications to your machine setup -- i.e. the addition of a Lantern -- American Heller offers a piloted push style counter boring tool. The piloted tool uses a fiber pilot guide to pilot off the pre-bore. Therefore, the piloted tool will be concentric to the pre-bore to within +/- 0.0005". The figure below illustrates a BTA/STS piloted counter boring tool in which the chip exhaust is through the ID of the boring bar.

http://www.unisig.de/en/unisig-deep-hole-drilling-machines/1...
Machines
Counter Boring
Counter boring enlarges existing holes formed either by prior drilling or casting, and is ideal for a large range of diameters, up to 630 mm.
Counter bore tools are designed to either: Pilot off a finished bore, with wear pads supported by the bore diameter, or pilot off the pre-bore, with wear pads supported by the pre-bore diameter, to achieve stringent concentricity requirements. (See Pull Boring for an alternate counter-bore method)

http://www.unisig.com/gundrilling-education/UNISIG-deep-hole...
Deep hole drilling reference, overview, definition, drill tube sizes
Tools for secondary machining and finishing
Counter-boring/reaming
External coolant
- Push configuration tools pilot off finished bore (wear pads hold by a finished hole diameter). They can also be designed to pilot off the pre-bore (wear pads supported by pre-bore diameter) for stringent concentricity requirements.

http://en.wikipedia.org/wiki/Counterbore
Counterbore
A counterbore is a cylindrical flat-bottomed hole that enlarges another coaxial hole, or the tool used to create that feature. A counterbore hole is typically used when a fastener, such as a socket head cap screw, is required to sit flush with or below the level of a workpiece's surface.
Machining
Counterbores are made with standard dimensions for a certain size of screw or are produced in sizes that are not related to any particular screw size. In either case, the tip of the counterbore has a reduced diameter section referred to as the PILOT, a feature essential to assuring concentricity between the counterbore and the hole being counterbored. Counterbores matched to specific screw sizes generally have integral pilots that fit the clearance hole diameter associated with a particular screw size (e.g., .191 inches for a number 10 machine screw). Counterbores that are not related to a specific screw size are designed to accept a removable pilot, allowing any given counterbore size to be adapted to a variety of hole sizes. The pilot matters little when running the cutter in a milling setup where rigidity is assured and hole center location is already achieved via X-Y positioning.