What is constant chord?
CONSTANT CHORD METHOD Defined as “The chord joining those points, on opposite faces of tooth, which make contact with the mating teeth when the centerline of the tooth lies on the line of the gear centers”. Constant chord measured where the tooth flank touches the flank of the basic rack.
What are the different method used for gear measurement?
The methods which are used for measuring the gear tooth thickness is 1) Gear tooth vernier caliper method (Chordal thickness method) 2) Base tangent method.
Which instrument is used for the measurement of gear tooth thickness?
Gear Tooth Vernier Caliper
The Starrett 456 Gear Tooth Vernier Caliper is designed to measure in . 001″ or 0.02mm the thickness of gear teeth at the pitch line (the chordal thickness of the teeth) using the distance from the top of a tooth to the chord. For the same purpose, it can also be used for measuring hobs, form and thread tools, etc.
What is base tangent principle?
PRINCIPLE: The length of the base circle intersected by the opposite flanks over a certain number of teeth is the base tangent length, also known as the span. For involute profiles, the distance between parallel lines embracing several teeth is a constant and equal to the base tangent length.
What are the advantages of the constant chord method?
The advantage of the constant chord method is that for all number of teeth (of same module) value of constant chord is same. In other words, the value of constant chord is constant for all gears of a meshing system.
What is a gear module?
“Module” is the unit of size that indicates how big or small a gear is. It is the ratio of the reference diameter of the gear divided by the number of teeth.
How do you measure the pitch circle diameter of a gear?
The pitch circle diameter is d = zm (where z = number of teeth, m = module). The pitch circle diameters are important numbers in locating the shafts of two mating gears. The center distance of two meshing gears is expressed as the sum of the pitch circle radii of the two gears.
What is gear tooth measurement?
The tooth thickness ts of a gear is defined as the arc length between opposite faces of a tooth, measured around the standard pitch circle. This is a length which cannot be measured directly, so in practice a different dimension of the gear is measured, which is then used to calculate the tooth thickness.
What is cyclic error in gears?
Thus the cyclic error may be defined as the mean value of the range of variation in the kinematic error of the gear taken for all cycles during one revolution. Smoothness of gear operation is also ensured by limiting the maximum permissible deviations in basic pitch and the involute profile tolerance.
What is pressure angle on a gear?
The pressure angle of a gear is also the angle between the line of action and the line tangent to the pitch circles of mating gears. Figure 57.26 illustrates the relationship of the pressure angle to the line of action and the line tangent to the pitch circles.
What is PCD in gears?
Pitch Circle Diameter (P.C.D.). It is the diameter of a circle which by pure rolling action would produce the same motion as the toothed gear wheel. This is the most important diameter in gears. It is defined as the length of the pitch circle diameter per tooth.
How is the constant chord of a gear measured?
The constant chord method does away with these difficulties. Constant chord of a gear is measured where the tooth flanks touch the flanks of the basic rack. The teeth of the rack are straight and inclined to their centre lines at the pressure angle as shown in Fig. 15.16.
How is contact between two gears always the same?
In involute gear design, all contact between two gears occurs in the same fixed, flat plane even as their teeth mesh in and out. Further, the contacting surfaces are always perpendicular to the plane of contact, so the dominant contact forces (in a well lubricated system) are always parallel to the plane.
Why are moment arms kept constant in gears?
This way, the moment arms are kept constant. This is key to minimizing the torque/speed variations which produce vibration and noise in lower quality gears. Note that the involute profile does not prevent the teeth from scraping each other every time they mesh, and this is the dominant source of wear.
How are teeth and tip diameters related in gear design?
The tip diameter (da) and root diameter (df) correspond to the top and bottom of the teeth. The reference diameter is used in gear designing and calculation. It has direct connections with other important gear parameters like the module (m), center distance (c) and pressure angle (α). The turning of 2 gears can be considered engaged turning