Analysis of the Deviation in a Low-Cost System for Stepless Digital Control of Conventional Lathe Spindle Speeds

Abstract

A conventional manual lathe electric motor drives the multi-stage gearbox transmitting torque to the spindle so that the workpiece makes contact with the machine tool at a given speed. The cutting speed is proportional to both the diameter of the workpiece and the spindle speed, however, the increments in spindle speed are limited. Manual lathe machines cannot be regulated at the optimum cutting speeds for all diameters. An innovative modernization of the main driveline of a TSB16 manual lathe is proposed in this paper, allowing for a cost-effective system for digital control of spindle speeds using an inverter. The inverter is controlled using an 8-bit AO (analog output) converter with special software developed with Visual Basic. The results of the analysis and various test runs with this new system for automated control of spindle rotation, showed that the required cutting speed can be achieved for any workpiece diameter. The deviation of cutting-speed of the upgraded system for any turning diameter is greatly reduced in comparison with the deviation of cutting-speed of a manual lathe. Finally, tests on this versatile system demonstrated a cost-effective method for modernizing the drive system of conventional lathe machines.

Keywords

• Turning
• cutting speed
• manual lathe
• speed control
• AO converter
• inverter