10 is mounted preferably on a slide assembly 22 for insertion into and withdrawal through a door of welding chamber 20 the welding chamber 20 could be a vacuum chamber such as those used in connection with high energy beam welding techniques including electron beam welding and laser welding and there would be appropriate seals see fig6 between the slide assembly 22 and abutting portions of chamber 20 and its door not shown in this figure are the high energy beam welding means vacuum maintaining means and the means to rotate the turret fixture 12 and swivel all of which are known in the art turning now to fig2 and 3 it will be seen that the turret fixture 12 is a large cylindrical member having a tapered internally threaded surface 24 terminating in a lower port 26 the turret 12 is supported on the rotary swivel assembly 14 for rotation therewith about a generally vertical axis the drill bit 18 illustrated is of a fairly conventional configuration and includes an upper body 28 forming an externally threaded tool joint portion 30 which is shown threadedly received in the internally threaded portion 24 of the turret fixture 12 for welding the bit is inverted from its normal operating position.