Drafting of involute spur-gears in AutoCAD-VBA customized

Abstract

The design of efficient and reliable gearing mechanism is governed, among other factors, by its ability to withstand the frictional contact condition and high bending stresses experienced at the tooth root. One of the major impediments facing designers is the effective drafting of gears to required configuration. For involutes spur gears, the geometry is tedious and time-consuming; and the geometric complexity increases with helical, bevel and worm gears. This study presents a model developed by utilizing the integration of VBA technology built in AutoCAD for the drafting of spur gear to standard configuration. The design was based on full-depth involute gears of pressure angles 14½°, 20°, and 25°; with module ranging between 0.3 and 25 mm, and number of teeth varying between 12 and 60. The algorithm employed the conventional manual drafting techniques by navigating the IDE of VBA with AutoCAD objects, properties, methods, events, and application of errors handling techniques that will ensure smooth running of the model. The model was tested by physically comparing gear tooth template of the automated and manual techniques for three cases of 14-tooth spur gears with pressure angles 20° and modules 6, 8, and 10; and gave a good representation of the tested cases. The model was implemented for simulation of cases of varying modules and varying number of teeth to investigate the significance of module and pressure angle on the gear structure and tooth profile. The model’s flexibility for simulation makes it a virtual prototyping tool that can enhance design, analysis and also makes it a veritable educational tool.

Keywords: Educational, spur gear, tooth-profile, drafting, AutoCAD-VBA.