Abstract: A worn titanium blade for a gas turbine engine has metal displaced at its aerofoil tip, so that the aerofoil can be dressed to restore it to length. The titanium is not amenable to cold forging, or to being entirely heated, a forge is therefore provided which has dies which contact only the immediate area containing the metal to be displaced. The dies are heatable so as to heat the said area by conduction and powered so as to apply suitable pressure in a way which brings about isothermal displacement of the titanium.

Abstract: Electro-discharge machining device including means for preventing the machining electrode from surging forward when the electrode breaks through a workpiece. The machining electrode is mounted on a first movable member including a portion which engages a motor driven second movable member. Once the first and second movable members are engaged, the first movable member is constrained to move toward the workpiece at a speed no greater than the speed of the second movable member. Sensing and signalling means control the speed of the second movable member by a signal representing the proximity of the first and second movable members.

Abstract: The spark rate across electro-discharge machine tool electrodes and workpiece, is counted and compared with a given pulse output from a reference source. A constant ratio of spark pulses to reference pulses indicates a stable machining operation. Variation in the ratio indicates breakthrough of the electrode, into e.g. a passage in the workpiece. A signal is derived from the ratio variation and is utilized to operate a switch to cut off power to the electrode. The invention is particularly useful where a bank of electrodes machine a row of holes into a passage, for it may be that some electrodes break through before others, making it possible for them to machine the back wall of the passage if power is not cut off.

Abstract: A pair of complementary rod electrodes, one of which machines the other, is added to the circuitry of an electro-discharge machining system in which holes are drilled into existing passages in a workpiece, by other machining electrodes. When a machining electrode breaks into the passage, the resulting sharp increase in electrical potential thereacross is prevented from affecting the electrode advance control mechanism because the mechanism only senses the low potential across the continuously machining rod electrodes. Thus the electrode which machines the workpiece is prevented from rapidly traversing the passage and machining the opposite wall.