ASSEMBLY FOR ATTACHING A BORING TOOL TO A DRILLING MACHINE INCLUDING A SAFETY DEVICE TO MINIMISE TOOL BREAKAGE

摘要

1348905 Machine tools O BILZ 18 Aug 1971 [5 Sept 1970 15 Jan 1971] 38714/71 Headings B3C and B3B To prevent axial back-pressure due to increased cutting resistance on a boring tool 25 from exceeding the pre-set axial feeding power of the driving machine, the tool spindle 2, 3, 4 of a machine tool assembly is axially slidable within a blind bore of the machine spindle 1 and connected thereto by means of a spline 24 and spring-loaded balls 15, held between pressure rings 13, 14, engaging a groove 18 in the tool spindle. Under normal conditions of feed, the spindles move axially together, but when the tool 25 encounters an abnormal resistance, the axial back-pressure forces the balls 15 out of groove 18 against the action of the spring 16 and the tool spindle slides deeper into the bore of the machine spindle 1 and thus prevents damage to the tool. The value of the back-pressure at which this occurs depends on the spring force which is pre-set by screwing retaining sleeve 11 on spindle sleeve 10. At the end of the operation when the tool is retracted from the workpiece any abnormal resistance to retraction is also accommodated by the tool spindle which again moves relatively to the machine spindle but in the opposite direction. In another embodiment, Fig. 3, the blind end 32 of the machine spindle bore contains a compression spring 26 which urges the balls 15, when the tool is out of work, to engage the top edge of a wider groove 18. In use the normal back-pressure on the tool spindle causes the balls to engage the bottom edge of the groove so that an electronic switch 30 is activated by a flange 27 on tool-spindle part 2 thus switching on the machine. In the out of work position the switch 30 faces space 28 and the machine is switched off as it is when in the overloaded position when the switch faces space 29. In Fig. 1 a device for indicating when the tool is overloaded comprises a coloured, reflective or radio-active ring 21 which is uncovered, or alternatively covered, by, for example, extension 19 of sleeve 11. The radio-active ring may be used to trigger a Geiger tube 22 and thence switch off the machine.