what is Worm Gears?
Worm gears are a unique type of staggered shaft gear and a specialized type of gear which utilizes threads on a cylindrical rod to create motion between shafts reducing speed.
The worm gear system is made of two components, the worm, and, the worm wheel. The speed reduction is a function of the threads on the worm engaging with the teeth of the worm wheel.
Worm gears reduce noise and dampen vibration and are compact. They will be made of hardened materials to last (and work) since worm gears generate a lot of heat.
How Are Worm Gears Made?
Worm gears are small gear systems; this is important because it is a very important method of power transmission design in many modern designs. Worm gears are known for their direction change and ability to move loads at high ratio speed reduction.
Worm gears have become an efficient power transmission design in industrial automation, robotics, and heavy equipment.
Worm gear assemblies are compact in form factor allowing installations in space-constrained areas allowing compact assembly which can also operate smoothly, quietly, and reliably under load.
A worm gear is and excellent choice of design as they allow for excellent torque transfer properties when partnered with a worm wheel, and anti-backlash properties also allow for its use in many application examples in automotive to aerospace, packaging to material handling, and other examples of industries at large.
The common method of manufacturing worm gears is in a process called hobbing; which is a form of precision machining utilizing a cutting tool called a hob. The hob has a gear tooth profile, and as such will have a profile similar to a generated worm gear that the hob will eventually engage.
Other than hobbing, worm gears may be produced by turning, high precision milling, and finishing grinding to have the geometry and prescribed surface finish achieved.
All of these manufacturing methods product worm gears manifested todays technology in manufacturing uses CNC (computer numerical control) which allows for improved dimensional accuracy and repeatability of modern worm gear sets.
How are Worm Gears Being Made?
Hobbing
Hobbing is the main process used to manufacture worm gears, especially in high-volume applications. Hobbing produces an accurate and precise gear tooth using hobs that are it’s unique to the required pressure angle and module or diametral pitch.
Hobbing is a cold working forging process, in which the punch penetrates exactly into the work piece to form the highly accurate and precise profiles of gears used for applications which ensure gear performance such as gearboxes, conveyor systems, machine tools, etc.
The tool of a hobbing machine is called a hob and is generally made of hardened high-speed steel or carbide, hence the hob has helical hob cutters.
The correct pressure, speed of rotation, and cold forging produce worm gears with precision tolerances, concentricity, and a surface finish that increases component life.
Today’s hobbing machines are fully automated and come in some variations. The result, gear heave many shapes and sizes, from miniature precision gears found in medical devices to heavy-duty worm gears found in industrial equipment, by way of hobbing.
These machines typically contain two primary spindles, one for clamping the gear blank (the work piece) and one for holding and rotating the hob, to maintain identical engagement while cutting the component geometry and producing uniform teeth.
Milling
Worm gears can be produced via milling by cutting gear teeth using a gear cutter on precision milling machines or jig grinders. Often times an indexing or rotary table is utilized for proper positioning of the gear blank to accomplish successive cuts sequentially.
The gear teeth are cut when the multi-edge rotating gear cutter produces the teeth to the gear profile (which is defined by the desired gear tooth geometry).
Milling is used for both standard and custom worm gears, especially in prototyping, small production runs or custom applications where a standard worm gear part would be impractical.
The accuracy of worm gear milling is mainly determined by the cutter and set up accurately, as small variations with the cutter or set up will affect the efficiency of power transmission through gear pairs and potentially increase noise.
Indexing is important in the milling process in order to ensure that all teeth are cut in the proper relationship and all conform to the design specification.
The advent of computerized numerical control (CNC) gear milling has espcially improved the accuracy and amount which worm gears can be produced which meet industry standards for worm wheel manufacturing.
Grinding
Grinding is a finishing technique that uses multiple cutting edges at high speed to remove material and produce the extremely high-quality finish required by precision worm gears.
Grinding is essential for worm gears made from hardened steel or other tough engineering materials, where the finish and form micro-geometry characteristics are important in reducing friction, noise, and wear during operation.
The grinding technique, often referred to as hard finishing, provides the final dimensions on worm gear teeth and enhances tribological performance to increase their operational life for high load or high speed worm gear assemblies.
The critical feature of the grinding process is the multi-axis grinder, which includes a bonded grinding worm, or threaded wheel, made from abrasives that are harder than the base material of the gear.
This machine presents extremely well controlled infeed (X-axis), vertical feed (Z-axis), and lateral shifting feed motion (Y-axis), producing the desired cut of the worm threads and the gear.
Worm gear grinding offers additional load capacity and efficiency, and is particularly important in the production of worm gears used in automotive transmissions and robotics and motion control applications.
Gears
A worm gear consists of a specially shaped worm and a worm wheel, composed of helical gears designed to transmit power, and rotational motion at a right angle, or from point A to point B, when power and motion are transmitted between non-intersecting gears.
Worm gears have three types of actual gears; spur, left-hand, and right-hand worm gears. The user will either need a left-hand or right-hand worm gear, depending on the direction of transmission for the application if a worm drive is needed.
The unique design of worm gear teeth, utilizing helical worm gears, allows worm gears to engage with the mating worm wheel efficiently, only allowing for limited backlash and quiet operation.
The quiet operation is important in applications where attempts are made to transmit power and motion with zero motion sensitivity. Worm gears can be made with bronze, steel, and special alloys that all have a different affect on durability, wear, and fit.
A proper lubricant and gear surface treatment are among the considerations for limiting wear and ensuring stable performance while using worm gear reducers and speed reducers gearboxes.
When it comes to worm gears; in knowing the difference between worm gears to other types of gears, such as bevel gear or planetary gears, and extending this thinking, you can choose the optimal option for Power Transfer for your application.
There are many worm gear suppliers available, but you should take a close look at their entire process of manufacturing quality worm gear sets, their capacity to produce custom gears, the engineering support offered, and their ability to meet industry standards or certifications and seek out ISO or AGMA certification.
Reputable gear manufacturers will provide workshops, and technical consultations, and can assist with rapid prototypes; most are precision-engineering solutions for OEMs or end-users in many different markets.
If you need custom worm gears, worm gearboxes, or precision-engineered gear assemblies, look for gear suppliers that have capabilities and facilities for advanced gear cutting, heat treating, material handling, custom post-processing, and more value-added services.
Dependability and long-lasting performance, cost effective, efficient, production run, reliability and the quality of the parts manufactured should ground your decision on a supplier’s worm gear manufacturing processes, facilities, and experience in producing standard to custom worm gearing solutions.
What Are the Different Types of Worm Gears?
One major advantage worm gears have is their ability to provide gear reduction and torque multiplications in a smaller space. In an industrial application or motion control application, a worm gear system is consumed of considerable speed reductions by using a simple, compact worm and wheel arrangement rather than a complex geared arrangement.
In general a worm gear set contains a large worm wheel (or gear) having a shallow helical thread that engages perpendicularly to mating worm shaft. This type of gear arrangement is favored for gear motors, conveyor systems and other types of power transmission that require compact, accurate, quiet operation.
The performance and efficiency of worm gears is very reliant on gear teeth positioning, precision of engineering and placement of its component parts while assembling the gear.
Since each specific worm gear mechanism requires the careful control of tolerances and custom tooth profiles, precise tooth contouring is very important to obtain the required mesh between the worm and the wheel or gear.
Any small misalignment or imperfection in a tooth or worm gear will result in excessive friction or a reduction in efficiency perhaps generating noise or causing an early gear breakdown.
Understanding the type of worm gear specifications based on load requirements, transmission ratio and speed control is critical for long-term reliability.
There are two main forms of worm gears: cylindrical (straight) and cone (double enveloping) worm gears. Additionally, worm gears can be classified on their face geometry such as straight, hobbed, or concave.
Of the two types of worm gears, cylindrical worm gears are most common, because they are versatile, easy to manufacture, and typically, can suit a large range of industrial gear drives and automated equipment.
Worm Gear Types and Classifications
Worm gear assemblies need to have the axial pitch of the worm equal to the circular pitch of the worm wheel so that power can be transmitted smoothly and efficiently.
The circular pitch is the distance between the points of adjacent teeth along the pitch circle of the gear. The axial pitch is the same measurement along the axis of the worm.
The worm shaft direction (right-handed or left-handed) and the number of starts or threads are also important parameters that define gear ratio, backlash, and mechanical efficiency.
The lead of a thread lead is defined as the distance a point on the thread advances in one revolution, and the lead angle is the angle formed by the thread helix and a reference plane perpendicular to the worm’s axis.
These key design parameters affect load capacity, reduction ratio, and smoothness of rotation, and affect the efficiency and load capacities of these assemblies using worm gears.
An optimal lead angle also means that the worm will provide the lowest frictional losses, which is important when full loads are applied, and in applications where the worm is under continuous duty cycles.
Non-Throat Worm Gears
Non-throat worm gears have neither a groove (throat) machined on the worm or worm wheel. In non-throat gear designs, the worm or worm wheel utilizes straight or simple helical geometry, which results in a single-point tooth contact when in operation.
Because of this, typically more wear occurs, and there is more friction loss compared to the throated types. Therefore, non-throat worm gears typically limit use to the light-duty application where cost-effective manufacture and simplicity of design is desired.
Non-throat gearboxes are usually used in basic mechanical assemblies, as well as hobby projects that have moderate loading requirements, where cost and ease of use, including light-duty use are applicable.
Single Throated Worm Gears
A single-throated worm gear has a curved or incurvate tooth profile on the worm wheel, allowing the worm to partially envelop the worm wheel.
This design increases the contact area to a continuous line rather than a point, and provides lower wear, smoother operation, and higher torque loads.
Single-throated worm gears are used in material handling systems, escalators, hoists and all applications requiring moderate torque capacity, not to mention, backdrivability preventing or enabling and improved efficiency.
Single-throated worm gears have a broad range of suitable materials to be used; the worm is usually hardened steel, while the wheel has a bronze or similar alloy to enhance the meshing characteristics and therefore service life.
Double Throat Worm Gears
The primary difference between single throat and double throat worm gears is the double enveloping (hourglass-shaped) design where there is a concave profile on the worm and the gear.
This form allows for the maximum surface contact area and alignment which enhances load capacity, mechanical efficiency, and shock resistance.
Double-throat worm gear sets are standard within industries with heavy machinery, elevators , critical automation drives, require high torque with little to no backlash, and seek efficient long-term usage.
It is very common for teeth profiles to be precision machined from the highest quality materials. The double throat worm gears also operate in relative silence while maintaining smooth and resilient movement through unrelenting daily use.
Double throat worm gears are made and suited to take a high load. The double throat design allows for a solid and exact connection between the worm and the gear with the most optimized connection for load and duration.
Worm Gear Mounting Methods
Proper and proper mounting of a worm gear assembly is basic to optimal transmission performance and the overall service life of the system.
Proper mounting, with careful, use of multiple and controlled contact points, minimizes localized forces, uneven wear, and excessive stress on the lead angle, which in-turn could easily lead to gear teeth failure or noise from the actual worm gear assembly.
Keyway
Keyway mounting uses one or more precision-machined square cutouts in the inner bore of the gear.
The keyway allows a key to be inserted between the gear and the shaft, offering a positive mechanical lock that effectively transmits rotational force and prevents rotational slippage between the gear and the shaft.
Keyways are frequently specified on gear reducer assemblies and heavy-duty power transmission systems.
Set Screw
Set screw mounting involves drilling a small hole through the gear hub, inserting a set screw, and tightening it against the shaft.
Set screw mounting is commonplace on light- to medium-duty gear and shaft connections. Set screw mounting is simple, adjustable, can be used for low- to moderate-precision mechanical assemblies.
Split
A split mounting utilizes a clamp that fits over a notched, or split part of the gear hub. When the clamp is tightened, compressing the hub, the friction creates a strong secure engagement, locking the gear and shaft together.
The split hub design supports quick installation and removal; applications requiring disassembly or adjustment in alignment such as prototype, test equipment, or quick-change gearbox are ideal candidates for split hub design.
Worm Gearboxes for Power Transmission
A gearbox is a mechanical unit encased in a tight enclosure for transferring torque and changing speed between a drive motor and a driven load.
A worm gearbox is a kinda gearbox with a worm shaft which has threads on it that mesh with a worm wheel, they are capable of high reduction ratios achieving an efficient torque multiplication in a small housing.
A worm by nature has numerous features, as the worm rotates it drives the worm wheel which provides smooth incremental motion through to the output load.
Typically worm gearboxes are applied in systems with a conveyor belt or processing application – packaging machines, powered gates, etc., where space, reliability, quietness, and backdriving resistance are prioritized.
When considering a worm gearbox/ reducer it is important to consider the reduction ratio, load capabilities of the gearbox, lubrication requirements, and mounting configuration which would be suited for the application to create maximum system efficiency while extending the lifetime of the system.
Worm Gear Threads and Transmission Ratios
The number of threads (or starts) on a worm determines how many teeth on the gear will advance per revolution. This number ultimately affects the gear ratio, speed control and efficiency of the drive system. For example:
- A single-start (single-thread) worm gear turns the worm wheel one tooth per revolution, thus yielding high reduction ratios and high torque multiplication—perfect for lifting and positioning machinery.
- A double-start (two-thread) worm gear will turn the worm wheel two teeth per revolution, providing moderate reduction (but faster rotational speed).
- Higher thread counts (triple-start or more) are used for systems that require higher speeds and less torque multiplication.
Worms with a high helix angle typically employ a single thread to reduce sliding friction and limit heat development.
However, depending on the required performance characteristics, lower helix angles and more threads may be appropriate when moderate speed increases are expected, and essentially, a smoother meshing is desired.
Arriving at the number of threads and helix angle is fundamentally important to achieve the required performance in industrial gear assemblies.
Further, it is essential that the worm threads are well-matched to the mating gear to provide efficient power transfer, minimize backlash, and extend working life.
In summary, the right mix of worm gear type, mount type, screw type, and gearbox specification could offer a much stronger, better, more efficient and more effective power transmission system for the many applications in the industrial sector, automation projects, and motion control space.
Identifying these differences can help designers and purchasers define the best answer to their mechanical design and intended applications.
What Are the Common Uses for Worm Gears?
There are many sizes and arrangements of worm gears, making them quite flexible in terms of application. Because of their varied sizes, shapes, and configurations they can be used in a range of items and machines.
The interaction of the wheel gear and worm gear causes a sliding motion that produces a low output speed and high torque. This arrangement provides efficiency and a unique action that allows it to perform a certain task with accuracy.
There are two distinct advantages to worm gears: efficient movement and unidirectional motion. Worm gears move in a 90-degree coordinated angle as most gear assemblies do, and will move in a unidirectional manner.
If you attempt to reverse movement of the gears, it does inevitable lock and will not change direction.
Worm Gear Usage
Noise
Worm gears are great for noise-related applications. Other types of gears have a high-pitched whine at high speeds, while worm gears operate very quietly. As a result of their noiselessness, public applications are preferred.
Fast Stopping
Worm gear design allows for rapid stopping, making them valuable in elevator applications. They should not be the sole part of the elevator’s braking system, however, and with other components, they add safety.
Space
Worm gears are used in many applications because of their compact nature because they require minimal space. Small space means efficiency needs but has limited space.
Shock Absorption
Worm gears are made of two types of metals: a harder metal that is made for the worm and a softer one for the wheel and it allows the worm gear to absorb shock loads from construction equipment and other heavy-duty applications.
Torsion
Off-road and construction vehicles based on varied terrains require differential torque to each wheel. The need for differential torque results from each wheel experiencing its own different surface.
Worm gears perform this function by keeping the vehicle in motion over uneven ground, while minimizing the chance of damage.
Tuning
The simplest worm gears can usually be found in string instruments. Worm gears are at the head of the instrument, making them easy to tune and adjust. It is easy for the musician to tune the instrument up or down by the pitch of the string.
Non-Reversible
Worm gears are another form of non-reversible gearing system are worm gears in lifts or elevators. Worm gear systems can serve as a fail-safe braking mechanism if the primary braking system fails.
Conveyor Belts
Worm gears are used a lot in conveyor systems as a one way motion and they can lock when the motion stops. When a conveyor is off, it needs to be stationary. Do not move. Worm gears create positional lock when motion is stopped. Therefore, the conveyor will not – slip – move forward!
Automatic Door Systems
Automatic sliding doors move both ways and need to stop moving once the right distance is reached. The stop mechanism is made with a worn gear that controls the end of travel movement.
Automotive Steering Systems
In an automotive steering system, the worm gear is connected to the steering wheel by the steering column. The degree of steering wheel movement relates to the gear ratio of the worm gear mechanism.
What Materials Are Commonly Used to Make Worm Gears?
Worm gears are used for gear reductions with reduction ratios found in the range from 20:1 to 300:1. The metals used for the worm gear assemblies must accommodate the stresses placed on it for worm speeds that are reduced or for worm torques that will be increased.
Worm gears are mostly manufactured from steel, iron, or bronze. In most cases, worm gear assemblies are made of a stronger and more durable metal than the metal used for the worm shaft.
Worm gears were manufactured from wood back in the day when hand-cranking mechanisms were first introduced for ship construction.
Today worm gears have been manufactured with materials stronger than wood for a longer service life due to recent advances in technology and metallurgy.
Materials Used to Make Worm Gears
Bronze
Because of its good mechanical qualities, bronze is frequently incorporated to produce worm wheels. Bronze is a copper alloy, and its brew varies according to the additional mates mixed with the copper, such as nickel, zinc, tin, and aluminum.
Worm wheels are built from tin bronze or aluminum bronze, as these alloys offer improved fatigue and friction resistance, and wear.
Brass
Like bronze, brass makes the wheel gear softer preventing wear on the worm shaft, and brass worm gear configurations works for light loads, as brass is only good for lower amounts of stress.
Steel
Both steel worm gears and worm wheels exist, but the normal arrangement would be a steel worm gear and a bronze or brass worm wheel.
Steel offers durability, tensile strength, and longevity. However, unless you want to spend more for a steel worm gear and a steel worm wheel, steel worm gears can fail, and repairs take time and money.
Plastic
Plastic worm gears are perfect for very light loads, for example where low torque is required, like automotive or robotic applications.
They will operate more quietly when used with metal worms and do not require lubrication. Additionally, plastic worm gears are lightweight and resistant to chemicals and corrosion.
Stainless Steel
Stainless steel worm gears are 303 and 316 grade stainless steel. Because of this, stainless steel worm gears will be very well suited in damp or wet environments and are resistant to oxidation and corrosion.
Stainless steel worm gears are often found in applications where hygiene is critical, such as food and beverage manufacturing.
Because stainless steel worm gears have uniform smooth surfaces combined with very durable materials and shapes, cleaning no longer a concern for all aspects of performance, reliability, and in hygienic environments.
How Should You Properly Lubricate Worm Gears?
Worm gears have high stress, torque, and movement on the gear at runtime, which means they will need lubrication, either oil or grease, to maintain an effective lubricant relationship between metal surfaces.
Types of lubricants usually used on worm gears include mineral-based lubricants derived from mineral oil (a by-product of crude oil), and others.
The main objective of lubricants on worm gears is to protect the worm drive from being damaged by friction and not working efficiently or corroding the driving components, and ultimately reduce operational problems for the gear system, help the gear operate more efficiently, add to the service life of a worm gear, and a variety of issues related to longevity of the worm gear in use.
To be clear, a lubricant will not stop a gear from being worn out. But, using a mixture of synthetic and natural additives offers better protection and increases life / probably to use a worm gear unit.
The lubricant can remove the risks of the worm gear not having contact on the wheel in the worm gear assembly, by maintaining viscosity. The type of lubricant you choose will be based upon the load and size of gearing.
Lubricating worm gears can be difficult because of the way they are designed. The primary issue with lubrication of worm gears is that since they are designed to slide, the sliding action expels oil and grease away from the working area of the worm gears.
The sliding motion of a worm gear requires a sliding metal with a low friction coefficient. The worm wheel is usually a yellow metal like bronze or brass, and the worm gear will be a hardened metal like steel.
Worm Gear Lubrication
Compounded
Compounded oil is a mineral based oil with rust and oxidation inhibitors along with four to six percent free tallow or synthetic fatty acids, which allows the oil to remain on the cylinder wall till the working temperature of 180°F (82 °C).
When the operating conditions exceed than the film strength of the bulk oil, the additives provide a buffer between the two interacting surfaces.
The lubricant viscosity is affected by the worm size, worm type, speed, and operating conditions. In a typical scenario a class 7 or class 8 compounded oil per American Gear Manufacturers Association (AGMA).
Extreme Pressure (EP)
EP (Extreme Pressure) oils can form a chemical layer on metal surfaces when subjected to pressure and temperature.
The chemical layer limits wear and welding. In particular, they perform well under shock & vibration. They protect steel parts very well. Like compounded oils, EP gear oils have temperature limits and they’re in AGMA grades 7 and 8.
Synthetic
There are two types of synthetic gear oils that can be used with worm gear applications, which are:
- Polyalphaolefin (PAO): PAO is compatible with low or high temperature applications, and with mineral oils. PAO does not damage seals or paint like standard synthetics, which is a big advantage, and rate as well as standard synthetics on lubricating properties in the high temp. service. PAO has an anti-wear mineral additive to improve the protective limits. PAO’s biggest disadvantage is cost.
- Polyalkylene glycol (PAG): While PAG has the same characteristics as PAO, it has a higher viscosity index than all synthetic or mineral fluids. PAG has anti wear ability, but does not have EP properties. PAG cannot be blended with any other fluids and can damage seals and paint.
Conclusion
- A worm gear is a staggered shaft gear that causes motion to be developed between shafts with threads that are cut into a cylindrical bar which provides speed reduction.
- Some advantages of worm gears include noise and vibration/finesse, as well as compactness.
- A worm gear system is the most compact type of gearing system, allowing for very high ratio speed reduction while still fitting into very small spaces.
- One major advantage of worm gears is they can give gear reduction and torque multiplication within a very small area.
- The variety of sizes, shapes, and styles means worm gears can fit into just about any device or machine.