GEAR HOBBING FORMULA PDF

GEAR HOBBING FORMULA PDF

The article “Helical Gear Mathematics Formulas and Examples” appeared in the May/June issue of Gear Technology. Summary The following excerpt is. Hobbing isa continuous gear generation process widely used in the industry between first and second cut so that a different formula isused. Spur Gear design formula for geometry, pitch, tooth clearance and critical functional data. Circular Pitches and Equivalent Diametral Pitches Table.

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Gear size, pressure angle, number of teeth…we introduce the basic terminology, measurement, and relational expressions necessary to understand basic gear technology. However, other methods are used too. Pitch is the distance between corresponding points on adjacent teeth.

Pressure angle is the leaning angle of a gear tooth, an element determining the tooth profile. Number of teeth denotes the number of gear teeth.

They are counted as shown in the Figure 2. The number of teeth of this gear is Dimensions of gears are fotmula based on these elements. Tooth depth is determined from the size of the module m. Please see Figure 2. Tooth depth h is the distance between tooth tip and the tooth root.

Addendum ha is the distance between the reference line and the tooth tip. Dedendum hf is the hobbinb between the reference line and the tooth root. Tooth thickness s is basically half the value of pitch p. In this section we introduce the basic parts of Spur Gears Cylindrical gears and dimensional calculations. The size of gears is determined in accordance with the reference hobbig d and determined by these other factors; the base circle, Pitch, Tooth Thickness, Tooth Depth, Addendum and Dedendum.

The Addendum and dedendum circle introduced here are a reference circle that cannot be seen on a gear, as it is year virtual circle, determined by gear size.

When a pair of gears are meshed so that their reference circles are in contact, the center distance a is half the sum total of their reference diameters.

Gears can mesh as shown in the Figure 2. Backlash is a play between tooth surfaces of paired gears in mesh.

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Mating gears also have a clearance play vertical to tooth depth. This is called Tip and Root Clearance cthe distance between tooth root and the tooth tip of mating gears. Spur gears with helicoid teeth are called Helical Gears. The majority of calculations for spur gears can be applied to helical gears hhobbing.

This type of gear comes with two kinds of tooth profiles in accordance with the datum surface. Hobbinv axis denotes the centerline of the gear. Reference diameter d of the helical gear with transverse system can be calculated from Equation 2. Reference diameter d of the helical gear with normal system can be calculated from Equation 2. When the gear surface is repeatedly subjected to load and the force near the contact point exceeds the material’s fatigue limit, fine cracks occur and eventually develop into separation of small pieces, thereby creating pits craters.

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The initial cause comes from small convex portions of the gear surfaces contacting each other and the local load exceeding the fatigue limit. As gears are driven and surfaces become worn in, local convex portions disappear and hobbinng load is equalized and pitting stops. Even after gear surfaces are worn in and load is equalized, with time more pitting starts to occur and pits get enlarged. These are some of the possible reasons of progressive pitting.

This is the condition in which the lubricant coating breaks down forula to overheating of local geag areas causing the deterioration of the gear surface from metal to metal contact.

Helical Gear Mathematics Formulas and Examples – May/June 1988

It is possible for this condition to forumla from moderate to break down. In the direction of gear sliding, groove like condition appears. This is part of abrasive wear and the following causes are possibilities. Wear that looks like an injury from abrasion or has the appearance of lapping. Below are some of the causes. Wear commonly occurring between metals in sliding contact.

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Wear reduction is related to type, pressure, speed, distance and lubrication. A minute portion of the material in contact welds adheres and the wear mechanism comes from peeling off of these by shearing force. This refers to the symptom of relatively large metal chips falling off from the gear surface due to material fatigue below the surface from high load.

The gear surface’s concave part is large and the shape and the depth are irregular. Because the applied shear force exceeds the material’s fatigue limit, fatigue cracks appear and grow leading to possible breakage of the tooth. Wear from the gear surface being subjected to intense repeated metal to metal contact which occurs when the oil film is thin and the lubrication is insufficient relative to the load and surface roughness of the gear. This condition tends to occur when operating at very low speed and high load.

Breakage that comes from an unexpectedly heavy load for one or several action cycles Normally, mistakes in design or manufacturing are not included. The fracture surface spreads fibrously from a starting point and indicates a sudden splitting. The cause is due to the load exceeding the tensile strength of the gear material.

This may come from the prime mover, driven mechanism or breakage of bearings or other gears which could cause biting of teeth, sudden stop, or concentration of load due to irregular tooth contact.

This is the case in which the root portions of gear are subjected to a repeated load exceeding the material’s fatigue limit. A fracture that starts in the corner of the gear root propagates until the tooth breaks.

The fractured surface is relatively smooth and the starting point can often ohbbing recognized by the beach mark shell pattern around it. This describes when a tooth separates from the body by shearing due to a one time extreme overload.

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The breakage is straight in the circumferential direction and appear flat as if machined. The nearby area shows plastic deformation.

It happens when the applied force exceeds the shear strength of the material. It happens when a high stiffness and strength gear is meshed with a gear which has a relatively low modulus of elasticity and weak material. Click Here to request the documents in PDF format. Tooth Depth and Thickness Tooth depth is determined from the size of the module m.

Diameter of Gears Size The size of gears is determined in accordance with the reference diameter d and determined by these other factors; the base circle, Pitch, Tooth Thickness, Tooth Depth, Addendum and Dedendum. Practice calculating the dimensions of gears. Calculations for the dimensions of gears.

Explanation of Terminology Pitting Bobbing the gear surface is repeatedly subjected to load and the force near the contact point exceeds the material’s fatigue limit, fine cracks occur and eventually develop into separation of small pieces, thereby creating pits craters. Initial Stage Pitting The initial cause comes from small convex portions of the gear surfaces contacting each other and the local load exceeding the fatigue limit. Progressive Pitting Even after gear surfaces are worn in and load is equalized, with time more pitting starts to occur and pits get enlarged.

Scoring This is the condition in which the lubricant coating breaks down due to overheating of local contact areas causing the deterioration of the gear surface from metal to metal contact. Slotting In the direction of gear sliding, groove like condition appears. Abrasion Wear Wear that looks like an injury from abrasion or has the appearance of lapping. Adhesion Wear Wear commonly occurring between metals in sliding formuls.

Spalling This refers to the symptom of relatively large metal chips falling off from the gear surface due to material fatigue below the surface from high load. Excessive Wear Wear from the gear surface being subjected to intense repeated metal to metal contact which occurs when the oil film is thin and the lubrication is insufficient relative to the load and surface roughness of the gear. Overload Breakage Breakage that comes from an unexpectedly heavy load for one or several action cycles Normally, mistakes in design or manufacturing are not included.

Fatigue Breakage This is the yobbing in which the root portions of gear are subjected to a repeated load exceeding the material’s fatigue limit. Shear Breakage This describes when a tooth separates from the body by shearing due to a one time extreme overload. Kohara Gear Industry Co.