<< Click to Display Table of Contents >> Navigation: MechDesigner Reference & User Interface > Dialog-Boxes > Dialog: Gear-Pair |
See: Add Gear-Pair
Gear Mesh: |
Inter-locking gear-teeth that allows a torque to be transmitted from shaft to shaft. |
External Gear Mesh : |
The gears have teeth that engage and diverge out from their centers-of-rotation. |
Internal Mesh : |
One of the gears has teeth that converge in to its center-of-rotation. |
Simple Gear-Pair : |
Two gears that rotate about fixed centers. |
Epicyclic Gear-Pair : |
One gear orbits around the center of the other gear. |
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Edit the Gear-Pair:
The Gear-Pair dialog-box is now open. |
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There are three tabs in the Gear-Pair dialog-box. Define tabAdjustments tabParameters tab |
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Gear Mesh and # Teeth Mesh - see Terminology above oExternal - or - oInternal center Distance - (Read-Only) see center-distance calculation in Adjustments tab Number-of-Teeth, z1 (Minimum =5) The number of-teeth on the input-gear - called the Driving-Gear Number-of-Teeth, z2 (Minimum = 5) The number of-teeth on the Driven-Part - or the output from the Gear-Pair. |
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Gear Segment Parameters Notes: A Gear-Segment is a gear that must oscillate. Gear 1 or Gear 2 can be a Gear-Segment Gear # Segmentation ◉Complete Gear - a normal gear ◉Gear Segment - to reduce the number of teeth. To reduce the number-of-teeth of Gear 1 or Gear 2 1.Click ⊚ Gear-Segment 2.Edit the Start Angle : Minimum = 0, Maximum = 360 3.Edit the Segment Range : Minimum = 0; Maximum 360 Each Gear will have an integer number-of-teeth. |
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Adjustments Gear-Slip (degrees) These parameters move Gear 1 and Gear 2 around the rotating center of each Part at the Pin-Joint. This parameter rotates the gear teeth, not the Part. Top-Tip: To keep the gears in mesh: Gear-Slip 2 = –Z1 ( Z2 × Gear-Slip 1) |
Clearance (move gears apart), jr This parameter increases or decreases the center-distance between the two gears. It is intended to add a small amount of Backlash (Play) between the gears - and thus it should usually be a +ve value. Although backlash may be introduced by increasing the center-Distance, it is more typical to thin the gear-teeth. The minimum value should be enough to accommodate a Lubricating Film. center-Distance Calculation If External Mesh = Clearance + (Module×(Number-of-Teeth Gear1+Number-of-Teeth Gear2)÷2) If Internal Mesh = Clearance + (Module×(Number-of-Teeth Gear1+Number-of-Teeth Gear2)÷2) Notes: Recommend Clearance - approximately. •Minimum: 0.006 × (center-Distance)0.5 •Maximum: 0.024 × (center-Distance)0.5 An alternative way to get a small amount of clearance is to reduce the size of the gear teeth and not to change the center-distance. We do not offer this design parameter. |
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Gear Tooth Parameters Edit Gear Tooth Parameters to define the shape of the gear teeth. |
Module m = P.C.D (in mm) ∕ Number-of-Teeth. |
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Pressure-Angle α - default = 20º Standard gears are 20º. Other standards are: •14º, 17.5º (weaker, quieter), •22.5º and 25º (stronger, noisier). |
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Addendum, ha - default = m. The radial height of the gear tooth from the Pitch Circle to the top of the tooth. |
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Dedendum, hf - default = m * 1.25. The radial depth of the gear tooth below the Pitch Circle to the root of the tooth. The Dedendum is usually larger than the Addendum to give clearance for the teeth. If 0.25<m<1, Dedendum is usually = m *.1.4 If m>1, Dedendum is usually = m *.1.25 |
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Root-Radius, rf - 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. |
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# Points along Profile The number of 'facets' along the gear tooth flank (and around the two Root Radii). To display Gears more accurately, increase the number of points. Otherwise, 4 is adequate, 10 is good. There is a CPU overhead when drawing Gear-Pairs, do not increase the number of facets without a good reason. |
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Gear Parameters all Read-Only Contact-Ratio: ε Contact-Ratio should not be less than 1.1. Contact-Ratio should be a minimum of 1.2 for working gears. See below for more details. 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 = Pitch Circle Diameter. PCD = Module * Number-of-Teeth, (m*z) Normal Backlash (mm) This is the gap (backlash) between the gear-flanks you can measure with a 'feeler gauge'. Normal Backlash is a function of the center Distance Adjustment parameter ONLY. Angular Backlash - Gear 1 (deg) jΘ1 This parameter gives the maximum rotation of Gear 1 if you do not move Gear 2. Angular Backlash is a function of the center Distance Adjustment parameter ONLY. Angular Backlash - Gear 2 (deg) This parameter gives the maximum rotation of Gear 2 if you do not move Gear 1. Angular Backlash is a function of the center Distance Adjustment parameter ONLY. |
TO OBTAIN |
FROM KNOWN |
USE THIS FORMULA |
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Pitch Diameter |
Module, m, number-of-teeth, N |
D = mN |
Circular Pitch |
Module |
pc = m.π = D.π ∕ N |
Module |
Diametrical Pitch, Pd |
m = 25.4 ∕ Pd |
Number-of-Teeth |
Module, m, Pitch Diameter, D |
N = D ∕ m |
Addendum |
Module, m |
a = m |
Dedendum |
Module, m |
b = 1.25m |
Outside Diameter |
Module, m, Pitch Diameter, D, or number-of-teeth, N |
Do = D + 2m = m (N + 2) |
Root Diameter |
Pitch Diameter, D, Module, m |
DR = D – 2.5m |
Base Circle Diameter |
Pitch Diameter & Pressure Angle |
Db = D cos μ |
Base Pitch |
Module, m, & Pressure Angle, μ |
pb = m π cos μ |
Tooth Thickness at Standard Pitch Diameter |
Module, m |
Tstd = π. m ∕ 2 |
center Distance |
Module, m, number-of-teeth, N |
C = m . (N1 + N2) ∕ 2 |
Contact Ratio for Spur Gears ( 1 < CR < 2 ) |
Outside Radii, Base Circle Radii, center Distance, Pressure Angle |
CR = (√R012 – Rb12 + √R022 – Rb22 – C sin μ) ∕ m π cos μ |
Backlash (linear) |
Change in center Distance, ΔC |
B = 2( ΔC )tan μ |
Backlash (linear) |
Change in Tooth Thickness, ΔT |
B = ΔT |
Backlash (linear) along Line-of-action |
Linear Backlash along Pitch Circle, B |
BLA = B cos μ
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Backlash, Angular |
Linear Backlash, D |
Ba = 6880 B ∕ D (arc minutes) |
Min. No. of Teeth for No Undercutting |
Pressure Angle, μ |
Nc = 2 ∕ sin2 μ Nc (20º) = ~17 Teeth |
Term |
Definition |
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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 right-angle 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 Line-of centers |
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 line-of-action 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 right-angle 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 |
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Term |
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Crowning: |
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End-Relief |
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Topping and Semi-Topping |
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End Radius and Edge Radius/End Relief Top Round/Semi-topping
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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
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