Patent GB-373138-A (GB)
Title: An improved tracer apparatus for use in a milling or like machine for copying (for example in die-sinking) and reproducing articles
IPC: B23Q35/32
Filed: 1931-02-14
Abstract: 373,138. Milling. NORBALLE, H. J., 85, Rickmans worth Road, Watford, Hertfordshire. Feb. 14, 1931, No. 4764. [Class 83 (iii).] Copying-mechanism; stopmotions.-In an electrically-operated milling-machine of the kind in which a tracer is traversed over a model and is thereby tilted or moved endwise so as to open or close electrical contacts which govern the movements of the tracer and of a milling cutter which operates on the work to produce a replica of the model, the tracer acts on the switch contact-arm through a coupling member which moves in a straight line parallel to the mean position of the tracer axis. The coupling member and tracer engage one another through a rounded surface on one and a recess on the other. In one form the tracer 17, Fig. 1, is removably attached to a spindle 15 mounted by means of a ball bearing 14 in a housing 10, the outer race of the bearing 14 being spherical to allow universal tilting of the spindle. A spring 22 acts through a collar 16 on the spindle to maintain it in the outermost position and a cylindrical recess 19 is formed in the inner end of the spindle to co-operate with a ball 21 slidably mounted in a bush 20 secured in a flange 11 of the housing 10. A lever 28 is secured by a screw 29 in a vertically adjustable manner to a bar 27 which is supported by horizontal trunnions 26 on a bracket 23 vertically adjustable on the flange 11. An adjustable screw 49 having a head 50 is secured to the lever 28 and is maintained in contact with the ball 21 by a spring 31 on a guide rod 30 passing through the lever. A contact blade 33 is insulated from the lever and is secured thereto by screws 34. Contacts 37, 39, 41 on the blade are adapted to co-operate with fixed contacts 38, 40, 42 attached to brackets 45, 43 and an insulating panel 44 respectively. The fixed contacts are connected to terminals 46 on the panel, which is covered by a plate 47, and an insulating bush 52 is provided for the electric leads. The spring 22 may be omitted, the spring 31 then serving to maintain the tracer in its outer position. The housing 10 is mounted in known manner on a travelling carriage which also carries the milling cutter or moves therewith and is driven in known manner towards and along the model. Pressure of the model on the tracer rocks the lever 28 and opens the contacts 39, 40, stopping the motion towards the model and allowing that along the model to continue, but should the pressure not be relieved thereby the lever 28 is further rocked, closing contacts 37, 38, and reversing the motion towards the model. A lateral obstruction rocks the tracer in the bearing 14 and causes the ball 21 to be moved rearwardly. Should the contacts 37, 38 fail to act when separated, further contacts 41, 42 are closed to stop the machine completely. In a modified construction a collar 55, Fig. 3, is attached to the spindle 15 and is pressed against the ball bearing 14 by a spring 54. The rear end of the spindle has a recess to engage a ball 57 received in a deep spherical recess in a plunger 56 slidable in the housing and urged forwards, within the range of stopnuts 59, by a spring 60. An annular recess 61 in the plunger acts on a lever 62, pivoted at 63, which carries movable contacts for engaging fixed contacts on blades 64. In a further modification, the plunger 56 is formed into a cylindrical rack by means of a number of annular grooves and co-operates with a toothed sector on the end of the lever 62. In order to reduce friction, the spindle may act on the balls 21 or 57 through rollers, four equally spaced rollers being preferably employed arranged tangentially to the spindle. In another modification, the plunger 56 may be formed with a conical or ball-shaped end to replace the ball 57.