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BASIC METHOD OF CALCULATING AND DRAWING SPUR GEARS

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EXAMPLE: DRAWING A SPUR GEAR WITH 15 TEETH, PITCH 22.44mm
 
1. Draw the profile of one tooth. Measure the distance across a tooth (see below), along the ‘root’.
 
 
 
 
2. To determine the circumference of the gears circle (root diameter):
 
 
3. To determine the circumference of the gear’s circle (root diameter) with 15 teeth :
 
 
4. If drawing the gears by hand, trace the profile with tracing paper and transfer each tooth to the root diameter.
If using graphics software, simply copy and paste each ‘tooth’.
 
 
5. Please note: Because distance ‘A’ is a ‘linear’ measurement (in a straight line) and it is being applied to a circle, you may need to add a couple of mm to the diameter, for all the teeth to fit.
To check if this is necessary, draw a circle to the root diameter (112mm in this case) and use a pair of dividers to mark the 15 ‘A’ divisions around the circle. If they are slightly out, draw another circle with a diameter a couple of mm larger, and try with the dividers again. If the ‘A’ measurements fit, carry on to the next stage.
 
 
6. Use a pair of dividers to mark the profile of the tooth on the tracing paper, onto the root circle.
 
 
 
 
7. Completed spur gear.
 
 
SET OF EXAMPLES - CALCULATING AND DRAWING SPUR GEARS
 
 
THE TRUE SHAPE OF SPUR GEARS
 
Spur Gears are found in the majority machines, including Lathes and Milling machines. A gear train made up of spur gears allow for the precise, efficient change of speed, which is an essential requirement for accurate machining.
 
TYPICAL PROFILE
 
 
 
 
CALCULATIONS FOR TWO MESHING SPUR GEARS 10 TEETH AND TWENTY TEETH
 
FOR GEAR 'A' (SEE DIAGRAM OF MESHING GEARS BELOW)
 
To determine the circumference of the gear’s circle (root diameter) with 10 teeth :
 
 
 
FOR GEAR 'B' (SEE DIAGRAM BELOW)
 
To determine the circumference of the gear’s circle (root diameter) with 20 teeth :
 
 
 
 
 
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