HEXAGON Newsletter 175 - May / June 2019

by Fritz Ruoss

The gear wheels of screw gears or crossed helical gears are actually normal helical gear wheels, as calculated with ZAR1 +. But the axes are not parallel, but crossed. In the normal helical gear, the sum of the helix angles is 0 (beta right-toothed - beta left-toothed), in the helical gear with crossed axes, it can be 1 ° to 90 °. Helical gear can be used for crossed and skewed axes. For example, with gear ratio 1 used for change of direction, and with a gear ratio 50 at pinion teeth number 1 as a replacement for worm gear, when the demands on load and service life are low. The strength is calculated according to Niemann.

ZAR9 is available now for the price of 650 Euro (single license).

Clamp parts could already be generated and printed as STL files. Now this is also possible for bolt and nut. So you can create a model of the bolted joint with 3D printer. This is especially interesting if self-designed bolts are used.

For better traceability of the fatigue strength diagrams, the intersection of the vertical working line tauk1-tauk2 with the fatigue strength curve (10 million cycles) is now listed as tauoz' as a numerical value. This is the permissible upper shear stress for fatigue strength for the given application. The lower shear stress is then tauu = tauk1, the permissible stress variation is taukh = tauoz '- tauu. The same with bending stress in FED3,4,9,10,13,14,15,16. Here, the intersection sigmao' in the Goodman diagram is displayed.

The load-extension curve can be exported as a table in Excel under "OLE \ Chart F-s".

The center line of a conical spring can be output for any clamping length as a step file.

Spring drawing: spring length in inches, if set to imperial units.

Operating temperature saved.

A model of shaft and hub can now be produced on the 3D printer. Only as an illustrative object, the press fit can of course not be produced in the required accuracy and surface quality with the 3D printer.

WN2,4,5,10,WNXE: Warning cffmin < 0

Warning cffmin < 0, if distance between form diameter tooth root to tooth tip diameter of counter wheel too small.

ZAR3+ generates an STL file for a gearbox housing consisting of 2 halves. You can print with the 3D printer 2 times and assemble a worm gear model.

In the diagram with the center distance as function of the helix angle, pitch diameter, tip diameter and root diameter of worm and worm wheel are drawn. An additional curve is drawn for the root diameter of the worm. Thus, you can estimate which helix angle is feasible for a high efficiency and a specific center distance, without the core diameter of the screw becomes too thin.

A thread of a screw has the same shape as the single-flight worm of a cylindrical worm gear. The shape of the cylindrical worm is again the same as a helical spur gear with a number of teeth 1 and large helix angle. The dimensions of a trapezoidal thread spindle can be calculated as a worm in ZAR3 +. The wedge angle of a trapezoidal thread is 30 °, then the pressure angle of the worm 15 °.

The module of the worm is P / pi, the pitch circle diameter of the worm is the pitch diameter of the thread. However, unlike gears, the head and root diameters of the thread are arbitrarily set or rounded, so you have to extra calculate tooth head height and root height factor for each thread size:

hf / mn = (d2-d3) / (2 * m), ha / mn = (d-d2) / (2 * m), axial modulus mx = P / pi, tan gamma_m = z * mx / d2

Number of threads of the screw z is the number of starts of the worm, normal 1.

Also normal ISO threads can be calculated as a screw. With pressure angle 30 °, calculate head and foot height factors also from outside diameter and core diameter.

With the mouse wheel you can enlarge and reduce size of drawings and graphics. Unfortunately, Windows 10 does not always work as it should, sometimes the background age is brought to the foreground and zoomed in when you just type in and unintentionally touch the mouse wheel. Therefore you can now turn off zooming with the mouse wheel ("Zoom Mouse Wheel?").

When releasing new programs had been neglected to adjust the price for the complete package. From 1.7.2019 the price for a complete HEXAGON package of 63 modules is 14950 EUR (previously 12900). Update price for a complete package is now 1200 Euros (previously 1000).