Spur Gear

Topics: Gears, Gear, Rack railway Pages: 5 (517 words) Published: March 3, 2013
The Spur Gear
Prepared by: Henry L. Paz

Objectives:
• • • • To describe the spur gear; To identify the spur gear parts; To draw spur gear; To follow faithfully the steps in drawing a spur gear.

Gear up and get ready to learn!

Let me ask you.

• What is a gear?

Gear is…

• Toothed wheel used to transmit power and rotating motion from one machine part to another.

Gear is…

• The simplest form of toothed wheel used in machinery with radial teeth parallel to the axis.

Types of Gear
• • • • • Spur Gear Helical Gear Bevel Gear Worm Gear Rack and Pinion Gear

Spur Gear

Helical Gear

Crossed Helical Gear

Bevel Gear

Spiral Bevel Gear

Hypoid Bevel Gear

Differential

Worm Gear

Rack and Pinion Gear

We’ll concentrate on Spur Gear.

The Principle

The Principle

Here’s the Spur Gear parts.

Here’s the Spur Gear basics.

• Calculate for spur gear details. • Follow steps in constructing spur gear.

Spur Gear Calculation • Given
–N = 20
–(Number of Teeth)

–P = 5”
–(Diametral Pitch)

– = 20 degrees
–(Pressure Angle)

Spur Gear Calculation

• Pressure Angle
• = 20 degrees

Spur Gear Calculation

• Pitch Diameter • D = N/P • 20/5 • 4” • 101.6mm

Spur Gear Calculation

• Number of Teeth •N=PxD • 20 D = Pitch Diameter

Spur Gear Calculation

• Diametral Pitch • P = N/D • 5” • 127mm

Spur Gear Calculation

• Outside Diameter • Do = (N+2)/P • (20+2)/5 • 4.4000” • 111.76mm

Spur Gear Calculation

• Addendum • a = 1/P • 0.2000” • 5.08mm

Spur Gear Calculation

• Dedendum • b = 1.157/P • 0.2314” • 5.87mm

Spur Gear Calculation

• Clearance • c = 0.157/P • 0.0314” • 0.79mm

Spur Gear Calculation

• Working Depth • hk = 2/P • 2/4 • 0.4000” • 10.16mm

Spur Gear Calculation

• Whole Depth • ht = 2.157/P • 0.4314” • 10.95mm

Spur Gear Calculation

• Root Diameter • D R = D – ht • 4.000” – 0.4314” • 3.5686” • 90.64mm

Spur Gear Calculation

• Base Circle • DB = D cos • 4 x (0.9396----) • 3.7588” • 95.47mm

Spur Gear Calculation

• Circular Pitch • Cp = D/N • 3.1416 (4/20) • 3.1416 x 0.2 • 0.6283” • 15.95mm

Spur Gear Calculation

• Circular Thickness • CT = CP/2 • 0.6283/2 • 0.3142” • 7.97mm

Spur Gear Calculation

• Chordal Thickness • tc = D sin (90/N) • 4 sin (4.5) • 4 (0.0784------) • 0.3138” • 7.97mm

Spur Gear Calculation

• Radius • R = ¼ Dradius • 0.25 x 2 • 0.5000 • 12.7mm

Spur Gear Construction
1. Draw outside, root and pitch diameters. 2. Draw the Base Circle.

Spur Gear Construction

Spur Gear Construction
3. Layout the Chordal Thickness on the Pitch Diameter. 4. Position the needle of the compass on the Chordal Thickness point and make an arc to intersect the Base Circle using the profile (R).  R = ¼ of Pitch Diameter Radius

Note:
• In actual drawing, we can round off calculated values. • Just remember to be consistent in offsetting values.

Summary
• The simplest form of toothed wheel used in machinery with radial teeth parallel to the axis. • Calculate the spur gear details before drawing. • Remember to follow the spur gear construction steps to produce good drawing.

The Spur Gear
Prepared by: Henry L. Paz

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