.. _node-bevel-gear-set:

**************
Bevel Gear Set
**************


.. figure:: /images/nodes-bevel_gear_set.png
   :align: right

   The Bevel Gear node.


The **Bevel Gear Set** group generates two bevel gears, pinion and a
bull gear, matched to one another. Typically, the term pinion refers
to the driving gear but it is used here to distinguish one gear
from another. The reason bevel gears are provided in pairs is because
changes in tooth counts on either gear will cause cone angle
changes. This will become apparent as you use the toolkit. Both pinion
and bull gears have their origin at world center, with the pinion
translated to properly oppose the bull gear.

See the section on :ref:`bevel-gear-notes` in the :ref:`working-notes`
for more detail on the math used to generate this node group.

Inputs
======

|FLOAT| Module
   The module for this gear.

|INTEGER| Pinion Teeth, Bull Teeth
   The number of teeth on the gear.

|FLOAT_FIELD_SINGLE| Pressure Angle
   The pressure angle in degrees. This effects the shape of the gear
   and plays a role in meshing. The default of :math:`20^\circ` is
   reasonable for most gears.

|FLOAT_FIELD_SINGLE| Face Width
   In a spur gear this would be known as the depth, basically the
   length of the cog.

|FLOAT| Shaft Angle
   The purpose of bevel gears is to change the rotational direction of
   a gear set; this attribute sets the angle. The default is
   :math:`90^\circ` which is likely for the majority of bevel gears.

|FLOAT_FIELD_SINGLE| Hole Radius
   The size of the center hole. This may be zero. The upper bound is
   constrained so the hole can't be larger than the dedendum.

|INTEGER| Flank Resolution
   This integer value sets the resolution of the sides of the gear
   cog. The default sets a reasonable default but set this lower if to
   control vertex count. Any large value may be reduced by distance
   merging in the implementation.

|FLOAT| Collar Depth
   This adds some control over the length of the collar or spindle
   extending from the part of the gear away from the gear teeth.

Outputs
=======

|GEOMETRY| Pinion, Bull geometry output
   Each output generates a gear in the bevel set.

|INTEGER| Pinion, Bulll teeth count
   For convenience, the number of teeth on this gear.

|FLOAT| Shaft Angle
   For convenience, the shaft angle this pair was set at.


Examples
========

Miter gears
-----------

The miter gear is the simplest example. Note that the object origin
for both gears is the apex of the pitch cone (this is a little easier
to see if you click on the image to view it in full resolution.) This
allows relatively easy alignment if you had to do this manually.

.. figure:: /images/eg-bevel_miter.png
   :width: 800

   A miter gear: both gears have the same number of teeth and the
   shaft angle is :math:`90^\circ`.

Bevel gears with 1:2 ratio
--------------------------

This example shows a bevel gear set with more teeth on the bull gear
than the pinion. The shaft angle is still set at :math:`90^\circ`.

.. figure:: /images/eg-bevel_16_32.png
   :width: 800

   Pinion with 16 teeth, bull with 32

Multiple bevel gear sets
------------------------

Multiple bevel gears can be employed in more complex
configurations. As with spur gears the module must be identical,
however, changing the number of teeth in a bevel gear set will alter
the pitch cone apex. Probably the best approach is to use only the
gear geometry from a single **Bevel Gear Set** node as shown below.

.. figure:: /images/eg-bevel_16_32_32.png
   :width: 800

   Pinion with 16 teeth, driving two bull gears with 32

The bull gear in this configuration was simply rotated
:math:`180^\circ`. The cogs lined up and didn't need any
other adjustments.