StarGear in detail

The user-friendly program interface conforms to the Windows Drag and Drop standard and can be operated easily. StarGear® for spur gears provides the basics for the design and calculation of spur toothed and helical toothed gears, externally toothed and internally toothed involute gears. No fictive mating-gear is necessary for the layout of individual gears. In addition to externally and internally toothed gear sets, it is possible to calculate and size single-stage planetary gear transmissions as well as rack and pinion sets.  The parameters can be chosen almost freely: - normal module up to 100mm,   can be graduated arbitrarily - number of teeth up to 10000 - normal pressure angle 5-40° - helix angle of 0 to 60° - any chosen addendum modification - any chosen height of cutter tooth and root

StarGear and 2D or 3D-simulation

The animation illustrates the kinetics of a gear set. This form of presentation permits an exact study of operational behavior. The test run analysis helps in finding where and what corrections have to be made at the tooth contact. The 3D-simulation program is an absolute necessity for the development of low-noise transmissions!

Specific gliding

The diagram of factor Zeta shows the specific gliding along the path of contact and therefore makes a fast and simple judgment on operational behavior. Changes in  shape, such as tip relief and smoothing are considered in the output of the diagram. The combinational analysis for tooth numbers provides the transmission ratio and center distance which deliver possible solutions for transmissions according to the module series of DIN 780, part 1. The diversity of solutions depends on the defined range for tooth numbers. The calculation of bearing strength, normal wear (pitting) and tooth fracture is made according to DIN 3990, part 11. The safety factors are determined on the basis of data such as number of revolutions, drive capacity or drive momentum, material (metal, plastics, sintered metal) and specified manufacturing data. The features of the most common materials are included. Furthermore, user specified material features can be entered into the calculation.

General outlook on all data

The integrated program routine Geometry is based on DIN 3960 and provides all relevant gear wheel characteristic quantities. Examples are:generated pitch circle, base circle, tip circle, root circle, center distance, contact ratio, diametrical pitch, theoretical base tangent length control measurement, theoretical ball measurements, active pressure angle, gliding factor Zeta,  exact calculation of usable tip and root circle diameters. The program section Tolerances provides the measurements for control needed in manufacturing  and manufacturing quality control. The calculation can be made according to DIN 3961-3967 (heavy machinery) or DIN 58405 (precision engineering) or according to specified data. The minimal and maximal span measurement, ball- and roll test dimension, backlash and angle of rotation as well as tolerances required for a single and double flank test are determined according to quality and measurement lists.

Worm gears and plastic

A variation in tooth thickness can be calculated by addendum modification in spur gear pairs of combination PA-steel . In worm gears, the expensive bronze gear could often be substituted by a significantly cheaper plastic gear. Nevertheless, addendum modification in worm gears is not included in the DIN. Star Gear provides addendum modification for single and multiple worms (Fig.7). This feature broadens the constructor’s freedom and makes the manufacture of significantly cheaper transmissions possible. The investigated combination has to transmit a rather large power with a pitch of 25. Hence, power and geometry are mostly determined. The most important criteria in determining the bearing capability of a PA-PA pairing is the rising temperature of the tooth flank. The elastic modulus of PA is less than 800N/mm² and therefore not of practical use at temperatures above 70°C (158 °F). Thus, the aim must be to stay as far under this temperature as possible. In the given example a gearing based only on PA is out of the question because even an efficient lubrication cannot reduce the surface temperature to below 90°C (194°F). A possible solution consists in a PA-steel-combination in which gear 1 runs with a surface temperature of 52°C (125,6°F)( Fig.5). It would then be possible to calculate an expressive fatigue life (e.g. according to Niemann/Winter).  StarGear offers not only a module for temperature calculation to complete the calculation of load capacity, but also offers various data on the properties of numerous plastics.

The influence of temperature

The aim of the following section is to investigate whether an existing transmission ratio of two steel gears can be alternatively calculated for PA. These considerations are normally made for economic reasons. Seen from a technological view, the application of plastic is called for when for example lubrication-free operation or noise and weight reduction are desired.