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FB Finished bore FC Flame cut Fabricated Construction Is a method of manufacturing sprocket or gear blanks by welding pieces of steel together and machining them to required dimensions. Linn Gear Co. has a tremendous amount of experience with this method of manufacturing and can supply large sprockets and gears of fabricated construction as economical alternatives to castings or forgings, particularly when required quantities are small. Face Width Is the width of the pitch surface. For herringbone gears, this includes the width of the surface containing both of the helices and the groove width. Finished Bore (FB) This term is used to identify a sprocket or gear whose center hole has been machined to a tolerance acceptable for mounting the part on a shaft. There are many methods of mounting sprockets and gears on shafts. A common method is the use of a key and set screw(s). Linn Gear Co. stocks a line of Finished Bore sprockets (FB's) which include a keyway and set screw. Flame Cut (FC) Refers to the process of cutting a sprocket from steel plate with a gas torch. The torch cuts the tooth profile on which the chain operates. No additional, close-tolerance machining process is typically applied. This type of nominal-tolerance tooth profile is acceptable for many applications using fabricated or cast chains. We do not recommend the use of flame cut tooth profiles with roller chains. Gear Ratio Is the ratio of the numbers of teeth in mating gears. (Driver/Driven) Gullet Space between two teeth of a sprocket or gear. HT Hardened teeth, indicates that the teeth of a sprocket or gear have been induction hardened HTD ® Is a Registered Trademark of the Gates Rubber Co. manufacturer of HTDr belts and sprockets; stands for High Torque Drive and refers to a particular style of toothed belt and sprockets compatible with those belts Helical Gears Helical gear sets run on non-intersecting, parallel shafts. Instead of being parallel to the shaft axis (as with spur gears), the teeth of a helical gear spiral around the gears shaft axis. Placing the gear teeth on this kind of angle increases the amount of tooth surface in contact during operation. This allows for transmission of a higher load with a given size of gear set relative to spur gears. Use of the helix angle also creates end-thrust forces, which attempt to push the gears away from each other axially. These forces must be allowed for in any gear set design. Helix Angle Is the angle between a tangent to the helix and an element of the cylinder. Unless otherwise specified, the pitch helix is referred to. Herringbone Gears Herringbone gear sets run on non-intersecting, parallel shafts. The tooth of a true herringbone gear is one continuous set of two opposing helices. The two helix angles come together in the center of the gear face to form a `V'. Gains in allowable load through increased tooth contact relative to spur gear sets of equal size are made. This is similar to helical gears, but with herringbone gears the end-thrust forces cancel themselves out. Cutting gears of this type is a difficult process which is made somewhat easier by machining a groove in the face at the point of the apex of the `V', creating a break in the middle of the herringbone gear tooth. This type of gear is technically a "Double- Helical" gear but is sometimes referred to as a herringbone if the center groove is narrow. Hob A specialized cutting tool used for cutting teeth in sprockets and gears by the hobbing method Hub A shoulder or flange protruding from the side of a sprocket or gear. Hubs provide width to a part, which is used, for mounting the part on a shaft. Hub Style Indicates the configuration of the hubs on a sprocket or gear. Type `A' indicates that the part has no hub; Type `B' indicates a hub on one side only and Type 'C' indicates a hub on both sides of the part. Type `A' sprockets are referred to as plate sprockets or "A plates". In the case of parts of fabricated construction the hub style indicates the projection of the hubs beyond the face width. Hypoid Gears Are gears similar in general form to bevel gears but designed to operate on non-intersecting axes. ID Inside diameter Idler A component in a mechanical power transmission system, which simply turns on its shaft without performing any ratio reduction or power transmission, functions. Induction Heat Treating A process of electrically inducing a magnetic resistance between a work piece and an electrode, causing the work piece to heat rapidly. Quenching (quick cooling) follows the heating process. The final result is a change in the steel's microstructure providing a harder wear surface. Linn Gear Co. has extensive experience with and equipment for hardening its products with this process. Induction hardening allows for hardening teeth only, leaving other areas of a part available for further machining. Involute Profile The flanks (or sides) of spur, helical, and herringbone gear teeth are generated by hobbing and shaping machines to approximate an involute curve as closely as possible. In simple terms, an involute curve can be created by tying a pencil to the end of a string and wrapping the string around a cylinder. Hold tension in the string as you unwind it from the cylinder. The curve drawn by the pencil as it moves out from the cylinder is an involute curve. The closeness with which the involute profile of an actual gear tooth approximates a theoretically perfect involute curve is one defining element of the quality of a gear. KW or KWY Keyway Keyless Shaft/Hub Connectors Devices designed to attach power transmission components such as gears or sprockets to shafts using expansion and compression forces between the bore and shaft. Linn Gear Co. recommends the B-Loc brand. Keyway A slot cut into both the bore of a sprocket or gear and the shaft onto which the part will be mounted. A square, steel `key' (straight or tapered) is inserted between the shaft and the sprocket or gear, allowing power to be transmitted between the two components. Length through bore Lead Is the axial advance of a helix for one complete turn, as in the threads of cylinder worms and teeth of helical gears. Length Through Bore Describes the overall width of a sprocket or gear measured axially at the center hole. Lightener Holes Are holes cut into the rim or web of larger sprockets and gears to reduce their weight, without reducing load carrying capacity. Lightener holes reduce shaft loads and shipping costs. LSB Sprocket A sprocket cut to run on the HTD® belts manufactured by the Gates Rubber Co. MD Mounting distance MH Max. hub (maximum allowable hub diameter) MOD Module, the pitch of a metric gear Mandrel Bore This term is used to indicate that the center hole in a sprocket or gear has no keyway, set screw(s), bushing or any other type of machined preparation for shaft mounting. Mandrel bores may be machined to a specified tolerance or a nominal tolerance. Mandrel bores are also referred to as plain bores or stock bores. Milled-To-Match This is a process of machining the ends of gear racks so that they may be mounted end-to-end with pitches running continuously across sections. A pinion may run across multiple sections of milled-to-match racks without interruption. Gear rack ends are normally sawed and may not be mounted this way without additional processing. Miter Gears Are mating bevel gears with equal numbers of teeth with axes, usually at right angles. Module (MOD) The ratio of the pitch diameter in millimeters to the number of teeth; a measurement of gear pitch expressed in metric Maximum Allowable Hub Diameter (Max. Hub) The maximum diameter that will clear below the sidebars of a chain when wrapped around a sprocket. If the hub diameter required for an application exceeds the max. hub of the desired sprocket a chain-recess style hub can be used. This is a hub which is below max. hub diameter at the sprocket face, then steps up to a larger diameter at a distance from the face that allows chain sidebar clearance. The larger diameter hub area is used for installation of set screws or oversized bushings. Mounting Distance (MD) Is the distance, for assembling bevel gears or hypoid gears, from the crossing point of the axes to a location surface of a gear, which may be at either back or front.  |
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