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Introduction
This article contains information regarding push pull cable controls and their use.
You will learn more about topics such as:
What is a Push Pull Cable
How Push Pull Cables are Made
Uses for Push Pull Cables
Push Pull Cable Control Installation Factors
And much more ...
Chapter One – What is a Push Pull Cable Control?
A push pull cable control is used for the transmission of multi directional precision control of mechanical motion. The many varieties of push pull cables or controls are adaptable to a wide range of applications and operations. Push pull assemblies are used in the automotive, aerospace, and heavy equipment industries to adjust and maneuver mechanisms.
The construction of a push pull cable control consists of two separate cables, with one that activates a device while the other shuts it down. The term “push” cable is a misnomer since it does not push but pulls as the other cable does.
Though push pull assemblies have a simple function, they are critical for designing and engineering mechanical components and analog systems. When determining the method for activating equipment by physical force through machinery, the first choice is commonly a push pull control cable.
The design process for push pull assemblies begins with examining the workload for the push mode. The movement of this inner wire can meet resistance, which can cause it to distort and buckle, especially when it extends from the conduit. To adjust for this phenomenon, the diameter of the inner wire can be increased to meet the needs of the workload.
The many factors, such as that of the inner wire in the push mode, are considerations engineers have to make when designing push pull assemblies. Though the basic function of a push pull assembly may be simple, precise and accurate calculations are necessary to ensure their successful performance.
Chapter Two – How Push Pull Assemblies are Made
The design and manufacture of push pull assemblies are critical for machine design. A well designed push pull assembly guarantees that powered functions work properly and experience a long lifespan. They are referred to as control cable assemblies, push pull assemblies control acceleration, actuation, braking, choking, drive latches, hood releases, rotation, and throttles, to name a few of their functions.
During the design phase of a push pull assembly, careful consideration is given to each of the components that make up the assembly since any defects in the assembly can radically influence its performance. Though there are different types of push pull assemblies, certain components are characteristic of all types.
The Making of Push Pull Assemblies
Casing of the Assembly
The casing of a push pull assembly, also known as the conduit, serves as a guide for the inner core. There are a variety of materials used to manufacture the casing, including galvanized steel, nylon, plastic tubing, or spiral wrapped wire. The casing is sufficiently flexible to allow the control system to be bent to meet routing needs. Various types of fittings can be added to the casing to increase the ease of operation.
Casings have an inner diameter where the cables are installed and an outer diameter that is strong and durable enough to protect the mechanism.
Bulkhead Terminal
The bulkhead terminal is swaged to the casing to secure the push pull control into a panel, bulkhead, or solid part of a mechanism. In most cases, they are made of steel, stainless steel, or brass.
Push Pull Assembly Inner Wire
There are several options for the inner wire of a push pull assembly. Though the load may be light, the assembly will still require some form of solid wire. A major consideration in selecting the wire is the pull position where the loads will be the greatest. In most cases, cable wires are made of stainless steel or galvanized steel due to their strength, endurance, and reliability.
As with the casing, the cable wire has to be flexible. Most assemblies are made with 7 x 19 or 7 x 7 wire due to their flexibility. In some cases, 1 x 19 wire is used, which is not as flexible.
Friction inside the casing or conduit can be a problem and cause wear on the assembly. For this reason, uncoated wire is chosen over coated wire. This avoids damage to the assembly, enhances its useful life, and prevents assembly failures.
The travel, or the distance from the end of the conduit to the bearing point of the cable, should be kept to a minimum. Longer travel increases the amount of friction and decreases output. With an increase in travel comes the likelihood of buckling the core. Travel should be kept to less than five inches.
Inner wires or cables are wound together in a uniform helical arrangement to create a strand. The varieties of strands typically contain seven to nineteen wires wound around a core or central strand. In the designation of a strand, the first number denotes the number of strands, while the second number is the number of wires per strand. A 7 x 7 cable has seven strands with seven wires per strand. Cables with more strands and more wires are more flexible.
Solid core wire is used in applications that require motion in the push and pull modes of operation. They are also used when a strand or cable is too flexible, requiring additional stiffness to actuate the process.
Fittings and Terminals
Fittings and terminals attach to the end of the conduit and secure the assembly. They prevent deflection when there is tension, system failure, or loss of control. Fittings and terminals assist in adjusting, actuating, accelerating, regulating, and releasing as well as offer precision and security.
Stamped Eyes
Stamped eyes are one of the most common forms of fittings. They vary in size according to the size of the cable and the size of the eye hole. Stamped eyes are swaged with hydraulic swagers for a tight secure fit.
Ball End
Ball end fittings come in a variety of sizes to fit different cable diameters. They are swaged on the end of a cable.
Ball Shanks
Ball shank fittings are used for push pull assemblies such as throttles, braking cables, and exercise cables to name a few. They protect cables from other metal parts and allow for rotation of the cable.
Thimbles
Thimbles are used when there are loops in the cable. They assist in preventing wear, keeping the loop open, and enhancing the cable’s strength. A thimble is a unique type of heavy duty end fitting that protects the cable.
Threaded Stud
Threaded studs are a way to attach a push pull assembly to a fixture. They are available in a variety of sizes to fit the needs of an application. As with other fittings, they are swaged to the cable.
Strap Fork or Eye
Strap Fork and Eye fittings are pull actuating options using a pin or bolt attachment. A strap fork is used when device actuation is pulled directly in between the forks. Strap eyes are used when the actuation needs to be rigid or straight. They are welded together to make them thinner to be able to fit in small spaces.
Marine Eye
Marine eye fittings are produced for the boating industry and are made of grade 316 stainless steel as a protection from the elements at sea. They have a shiny and appealing finish that makes them aesthetically attractive but are durable and resilient. The corrosion resistant materials and special treatment of marine eye fittings make them more expensive.
Handle and Knobs
Handle and knob fittings are the types of push pull control cable fittings that most people use for lawn mowers, chain saws, and other garden implements. They are used as actuators, methods for performing adjustments, rotating, releasing, and acceleration to name a few.
The end fittings, terminals, caps, handles, and knobs described above are a small sampling of the many available types. Specialized push pull controls have connections and fittings designed to meet the needs of their application.
Leading Manufacturers and Suppliers
Chapter Three – Uses for Push Pull Cable Controls
The uses for push pull cable controls are endless and involve a wide range of industries from highly sophisticated aerospace components to backyard tools for gardening. They are designed to control processes, adjust mechanisms, and activate various parts during an operation.
With the advent of the computer age, it could be assumed that push pull cable controls would no longer be necessary. In actuality, push pull control cables have become essential for programming automated equipment. The versatility and adaptability of push pull controls and their ability to perform accurately and flawlessly have made them ideal for the many computer run functions.
How Push Pull Cable Controls are Used
Aerospace Uses
Modern aircraft require dependable components and are capable of meeting the needs of safe control and excellent performance. Push pull cable controls provide the capabilities for remote activation of aircraft mechanisms.
Implements for aircraft have to be able to endure high tension and compression forces that are encountered during flight, which makes push pull cable controls an ideal solution. For aircraft controls, they are made in short lengths to prevent vibration and bending under compression.
Marine Uses
Push pull controls have found many uses in boats. They mechanically connect the control head to the clutch and throttle. They are an ideal solution for boats with one or two control stations and have a cable length of fewer than 50 feet. In a single lever control, the lever is pushed forward to engage the clutch. As the lever continues to be pushed forward, speed is increased. The reversal of the actions is created by pulling back on the lever.
Lawn Mower
Push pull control cables for lawn mowers are used as throttle cables that control the speed of the lawn mower. In modern lawn mowers, the push pull control cable is connected directly to the carburetor’s intake valve. The push max load for a throttle cable is 10 lbs. while the pull load is 25 lbs.
Usage in Trucks
Heavy duty equipment, such as trucks, rely on push pull control cable assemblies to activate several operations and processes. There are cables for front winch control, dump body control, shift control, transmission engage control, defrost control, engine stop, and throttle control, to name a few. These different push pull control cables make operating heavy duty trucks easier and more efficient.
The few push pull uses described here are a very small fraction of the many ways that push pull control cables are used. They are found in industrial machinery, programmed applications, construction equipment, and many other applications. Their main functions of activating and controlling processes accurately and with great precision are the reasons they are so widely used.
Chapter Four – Push Pull Cable Control Installation
Push pull control cables are at the heart of motion control systems. In the production of cable assemblies, certain factors have to be considered such as the workload in the push and pull modes, where the workload in the push mode is the most critical. Other design considerations are abrasion, cycle life, flexibility, the environment, and safety.
The versatility and reliability of push pull cable controls make them an alternative to electronic, hydraulic, and pneumatic systems. Several methods are used to install push pull control cables, which are determined by the application, structural factors, and accessibility.
Installing Push Pull Control Cables
Riveted Method
The rivet method of installation is the most common. Normally, two rivets are placed perpendicular to each other at each end of the mechanism. Rod ends with hollow shanks need extra care during installation. Depending on the application, the rivets can be inserted using a rivet gun or be hammered in.
Bolt and Nut Methods
Bolt and nut methods for securing push pull cable assemblies require the use of bolts capable of withstanding the tension and compression placed on the assembly. The choice of the type of bolts depends on the size of the push pull assembly, with larger assemblies requiring larger more substantial bolts. Nuts for securing push pull cable controls are normally fiber or nylon lock nuts that lock the connection and prevent vibrations.
Welding Push Pull Cable Controls
Welding of push pull cable controls in place is used with push pull assemblies made of steel or stainless steel. Though welding tightly secures the push pull assembly, it requires exceptional skill and extra care to ensure the proper placement and fit.
Threaded Fittings
Push pull cable controls with threaded fittings are most effective with shorter length designs and are used with assemblies that are eight to nine inches in length. The threaded method allows both ends of the rod to be adjustable, although the most common practice is to have one end immobile. The advantage of having both ends adjustable is the ability to make a wide range of changes and adjustments.
Calculating Workload
Of the many factors regarding push pull cable assemblies, the workload is the most critical and must be carefully calculated to ensure the proper performance of the mechanism. The workload factor is the amount of force required to power a device.
The main consideration is the pushing mode, where a greater amount of weight is in the workload. The diameter of the cable can be adjusted to match the increase in the workload in the push direction. The workload in the pull direction is more flexible and can be easily adjusted.
Backlash in Actuation
Backlash is the motion lost in actuating the push pull cable. This particular factor is normally accounted for during the design phase but can be altered by increasing the number of bends and tightening the number of bend angles. By minimizing the number of bends and angles, backlash can be decreased and performance enhanced.
Every push pull control cable installation is unique to the application for which it is being completed. The four connection methods described above are a few examples of methods used. The method of installation depends on the types of fittings on the push pull control cable and where the cable is to be installed.
Backlash, vibrations, abrasions, and especially workload are factors that apply to all push pull control cable installations and are normally addressed during the design phase but should be considered when the assembly is in use. The most critical factor to consider when purchasing push pull controls is the quality and reputation of the manufacturer, which can greatly reduce future problems.
Conclusion
A push pull cable control is used to transmit multi directional precision control of mechanical motion.
The construction of a push pull cable consists of two separate cables, with one that activates a device while the other shuts it down. The term “push” cable is a misnomer since it does not push but pulls as the other cable does.
Referred to as control cable assemblies, push pull assemblies control acceleration, actuation, braking, choking, drive latches, hood releases, rotation, and throttles to name a few of their functions.
During the design phase of a push pull assembly, careful consideration is given to each of the components that make up the assembly since any defects in the assembly can radically influence its performance. Though there are different types of push pull assemblies, certain components are characteristic of all types.
The uses for push pull cable controls are endless and involve a wide range of industries from highly sophisticated aerospace components to backyard tools for gardening. They are designed to control processes, adjust mechanisms, and activate various parts during an operation.
Leading Manufacturers and Suppliers
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