See: Add GearPair
A GearPair is a kinematic joint.
Before you add the GearPair:
•  The input to the GearPair is a rotatingPart, with a known motion  it is a Green, kinematicallydefined Part. 
•  The output is a rotatingPart that is not kinematicallydefined, 
After you add the GearPair, the elements are:
•  The output Part becomes kinematicallydefined. 
•  The motion of the output Part is a function of the ratio of the gearteeth and the motion of the rotatingPart at the input. 
To edit the parameters of the GearPair, open the GearPair dialogbox:
1.  Click the GearPair element in the AssemblyTree or the graphicarea. 
The GearPair element should show in the SelectionWindow.
2.  Rightclick the GearPair in the SelectionWindow to show a contextualmenu. 
3.  Click 'Edit element' in the contextualmenu 
There are three tabs in the GearPair dialogbox. 
Gear Mesh and # Teeth Mech Gears can have an internal or external mesh (also called 'tooth form').
 or 
Centre Distance  [ReadOnly (see also Clearance in the Adjustments tab)] If External Mesh: CentreDistance = Clearance + [Module × (NumberofTeeth Gear1 + NumberofTeeth Gear2) ∕ 2] If Internal Mesh : CentreDistance = Clearance + [Module × (NumberofTeeth Gear1  NumberofTeeth Gear2) ∕ 2] NumberofTeeth, z1 [Minimum =5] This is the Gear on the DriveR Part that has a Green PartOutline before you do Add GearPair. NumberofTeeth, z2 [Minimum = 5] This is the Gear on the DriveN Part that has a Blue PartOutline before you do Add GearPair. The Part becomes Green after you add the GearPair. 

Gear Segment Parameters Gear N Segmentation
GearSegments are incomplete gears. If you want to reduce the numberofteeth of Gear 1 or Gear 2 so that the Gear is 'incomplete', click GearSegment Gear 1 is the 'input gear' Gear 2 is the 'output gear' Start Angle : 'Start Angle' of the Gear Segment for the Gear [0 – 360]. 0º is at the point between the gears when the Master Machine Angle = 0. Segment Range : How much of the Gear you want as a Gear Segment To see one GearTooth Segment Rangemin = RoundDown[NoofTeeth[total] ÷ 360 ] They have an integer numberofteeth. 
Adjustments GearSlip [degrees] These two parameters move Gear 1 and Gear 2 around the rotating centre of each Part at the PinJoint. This parameter does not rotate the Part, only the Gear. To adjust GearSlip, and keep the gears in mesh, you must adjust the gears by –vegear ratio. TopTip: To keep the gears in mesh: GearSlip 2 = – Z1 ∕ (Z2 × GearSlip 1) Clearance [to move gears apart] This parameter increases or decrease the centredistance between the two gears. It is intended to add a Backlash [Play] between the Gears  and thus it should normally be a +ve value Notes: Recommend Backlash:
An alternative way to get a small amount of backlash is to cut the gears more. The gear teeth become slightly smaller but the centre distance remains the same. We do not offer this design parameter. 
Gear Tooth Parameters Edit the Standard Gear Parameters to define the gear teeth. 

Module [m] = P.C.D (in mm) ∕ NumberofTeeth. [Fewer teeth for a P.C.D., means each tooth is bigger]. The default module is calculated from NumberofTeeth, CentreDistance and External Mesh. 

Pressure Angle [α] [Default = 20º]. Standard gears are typically 20º. Other 'standards' are: 14º (weaker, quieter), 17.5º, 22.5º and 25º (stronger, noisier). 

Addendum [Default = m]. The radial height of the gear tooth from the pitch circle to the tip of the tooth. 

Dedendum [Default Value = m * 1.25 (when m > 1)]. The radial depth of the Gear tooth below the Pitch Circle to the root of the tooth. It is usually larger than the Addendum so there is clearance for the Gear Teeth to mesh without binding. If 0.25<m<1, Dedendum is typically = m *.1.4 If m>1, Dedendum is typically = m *.1.25 

Root Radius, or 'Flank Radius' [Default is 0.3 * m] The small fillet between the Flank and the Root of the Gear Tooth. Note: In reality, if the gear is manufactured from a Hob/Rack Cutter, then the root of the gear is a Trochoid. 

# Points along Profile' [and # Points Root Radius*2] The number of 'facets' along the gear tooth flank [and around the two Root Radii]. To display Gears more accurately, then increase the number of points. Otherwise, 4 is adequate, 10 is good. There is a CPU overhead when drawing GearPairs, do not increase the number of facets without a good reason. 

For information: Working Clearance = Dedendum  Addendum Working Depth = Addendum * 2 Whole or Tooth Depth = Addendum + Dedendum Pitch Circle Diameters: d1= z1*m ; d2=z2*m, Addendum = 1.0*m; Dedendum = 1.25*m ; Root Radius =~0.3*m Tip Diameter = d + 2*m Root diameter = d  2.5*m Centre Distance = (d1 + d2) / 2 

Gear Parameters There are a number of parameters that are available for Gear Analysis. ContactRatio: Each gear tooth is in contact with another gear tooth as it moves through the meshing position. The 'ContactRatio' gives the numberofteeth that are in contact with another, on average, as they pass through the meshing point. A contact ratio between 1 and 2 means that contact alternates between two and one pairs of teeth in contact at any one time. Gears that have a 'high' ContactRatio are smoother and quieter. The ContactRatio of an Internal GearPair is higher than that of a similar External Gearair, even greater than 2. ContactRatio should never be less than 1.1. ContactRatio should nearly always 1.2 or greater. If the ContactRatio is too low, then consider:
Working Clearance = Dedendum  Addendum The distance between the top land of a gear tooth and the bottom land of the gear with which is meshed. Gear 1 PCD & Gear 2 PCD PCD is Pitch Circle Diameter of each Gear. PCD = Module * NumberofTeeth, m*z Normal Backlash [mm] If you move the Gears apart, with the Centre Distance Adjustment Parameter, then there is backlash between the Gears at the mesh point. This is the gap between the gearflanks with a 'feeler gauge'. Angular Backlash  Gear 1 [deg] This parameter gives the maximum rotation of Gear 1 without moving Gear 2, as a consequence of moving the gears apart with the Centre Distance Adjustment Parameter. Angular Backlash  Gear 2 [deg] This parameter gives the maximum rotation of Gear 2 without moving Gear 1, as a consequence of moving the gears apart with the Centre Distance Adjustment Parameter. 
Image Courtesy of the Internet  an image available from so many sources it is difficult to know which is the original source. 


Term 
Definition 

Addendum: 
the height of the gear tooth above the pitch circle diameter 
Backlash: 
the angle the output shaft of the gearbox can move without the input shaft moving 
Base Circle: 
an imaginary circle used in involute gearing to generate the involutes that form the tooth profiles 
Bevel Gears: 
used for rightangle applications. There are two types of bevel gears which are straight and spiral 
Center distance: 
distance between the axes of two meshed gears  Length of the Lineof Centres 
Circular Thickness: 
the thickness of the tooth on the pitch circle. 
Dedendum: 
the depth of the tooth below the diameter of the pitch circle. 
Diametrical Pitch: 
the teeth per inch of the diameter of the pitch circle 
Differential Gear: 
a bevel gear which allows two shafts to rotate at a different speed. 
Gear: 
a wheel with teeth that meshes with another wheel with teeth to translate motion. 
Gear Center: 
the center of the pitch circle. 
Gear Train: 
two or more gears meshed by their teeth. A gear train generates power speed through the meshed gears rotating 
Gear Ratio: 
the ratio between the numbers of teeth of meshing gears. 
Helical Gear: 
gear with the gear teeth cut at angles 
Line of Contact: 
the line or curve along which two tooth surfaces are tangent to each other 
Involute: 
the curve which describes a line which is unwound from the circumference of the gear 
Pinion: 
a small cogwheel which fits into a larger gear or track. 
Pitch Circle: 
the curve of intersection of a pitch surface of revolution and a plane of rotation 
Pitch Diameter: 
the diameter of the pitch circle 
Pitch Radius: 
the radius of the pitch circle 
Planetary Gears: 
a system that consists of three components: the sun gear, ring gear, and two or more planet gears. The sun gear is in the center, the ring gear is the outermost gear, and the planet gears are the gears surrounding the sun gear inside the ring gear. 
Pressure Angle: 
the angle between the lineofaction and the normal [90º, perpendicular] to the surface of the tooth 
Spiral Bevel Gears: 
shafts whose axes are perpendicular [90º] to each other and are used in rightangle applications 
Spur Gear: 
connect parallel shafts which have involute teeth that are parallel to the shaft 
Sun Gear: 
a gearwheel that rotates around its own axis and has other gears (planet gears) that rotate around it 
Torsional Strength: 
the measure of the amount of torque that a radial shaft can sustain during its rotation in a mechanical system 
Working Depth: 
the max depth a tooth of one gear extends into the tooth gear of a mating gear 
Worm Gear: 
a gear with one or more teeth with screwed threads 
Image 
Term 

Crowning: 

EndRelief 

Topping and SemiTopping 

End Radius and Edge Radius/End Relief Top Round/Semitopping


Definition of Circular Pitch, p Circular Pitch = pitch circle circumference[pi.d] / number of teeth[z] ; p = Π.d / z Module = Pitch Diameter[d] / Number of Teeth[z] ; m = d/z Circular Pitch[p] / Module[m] = pi ; p/m = Π Pitch Diameter[d] = module[m]*number of teeth[z] ; d = m.z α 