Automotion Components Spur Gears
Automotion Components produce a wide range of high-quality gears, including spur gears, precision-ground Spur Gears, Anti-backlash Spur Gears, Spur Gear Racks, Helical Gears, Mitre and Bevel Gears, Worm Gears and Wheels. We have one of the largest selections of Spur Gears available in the UK. We mainly concentrate on Precision Spur Gears from module 0.3 - 5. Our Spur Gears are produced extremely accurately to JIS B 1702-1 standards (mainly class 8/9, but in the case of plastic gears, class 9-11).
What are Spur Gears?
Spur Gears are cylindrical toothed wheels in which the teeth are aligned parallel to the axis of rotation. Spur Gears interlock together to transfer and multiply torque from one shaft to another parallel one. Alternatively, to convert rotational motion into linear motion, Spur Gears can interact with a Spur Gear Rack – this is essentially a Spur Gears with an infinite radius (i.e. rack and pinion). When interlocked, the gears rotate in opposite directions. There are a great many different pairing combinations (based on the module sizes) but they may be noisy at high speeds. We have Spur Gears in a variety of materials and sizes either in stock or with a very short lead time!
Why choose a Spur Gear?
Spur Gears are a popular choice for precision engineering applications because they can be manufactured to extremely high tolerances, and due to ease of manufacture, they are often a financially economical choice of gear. Loading a Spur Gear creates no additional axial thrust and they are therefore a highly efficient method of mechanical power transfer (generally 97-99% efficient).
Gear efficiency comparison table
| Gear Type | Efficiency (%) |
| Spur | 97-99 |
| Helical | 97-99 |
| Bevel | 96-99 |
| Worm - single | 45-55 |
| Worm - double | 55-65 |
Spur Gear module size is defined as the reference diameter (d) divided by the number of teeth
Addendum (da) and dedendum (dr) line diameter is related to the reference circle diameter (d)
Spur Gear terminology
Perhaps the most important need-to-know terminology for Spur Gears are: 'module' and 'reference line'. These terms are actually interrelated.
The reference line/circle is also sometimes known as the pitch circle - shown in red on the image to the left. It is the line on the side profile view of the Spur Gears on the level that marks the change from the addendum to the dedendum. The reference circles of two mating gears must touch; the reference radii of two gears must be added together to calculate the distance required for effective gear meshing. The diameter of the reference line is referred to as d.
The module is an important concept because it allows us to easily find and select mating gears. In the past, Spur Gears were defined by their reference circle diameter and the number of teeth – which is acceptable, but slightly unhelpful as the size of the teeth is more important for meshing gears. As part of an international standardisation of naming conventions, the term ‘module’ was defined as the reference (or pitch) diameter divided by the number of teeth. Note that the module is never referred to as a ‘modulus’. Knowing the module size of a gear is helpful for ISO standard applications because it tells us the size of the teeth – which in turn tells us that gears with the same module can be used together. There are various standard module sizes, such as 0.5, 0.8, 1.0, 1.25… 20, 50 etc.
Example calculation: what is the reference circle diameter (d) of a module 2 gear with 20 teeth?
The reference diameter (d) is 2×20 = 40mm.
Also, the addendum line diameter (da) is 44 mm, and the dedendum line diameter (dr) is 35 mm (please refer to the equations to the left hand side of this box).
Example calculation: I've found a gear that has 44 teeth and a reference line diameter of 66 mm. How can I choose a gear to pair with it?
The module of the gear is 66/44 = 1.5.
Gears with the same module can be used together, so you can use any module 1.5 gear with this gear. The number of teeth you choose will depend on to what extent you want to increase or reduce the speed.
Spur Gear material options
We can provide Spur Gears in a variety of materials, including but not limited to: carbon steel (S45C), stainless steel, brass, and thermoplastic polymer (polyacetal; PA – also known as polyoxymethylene; POM). The material of the Spur Gear affects the torque transmitted (please see below for more details on torque as applied to Spur Gears). For example, a module 0.8, 25-tooth Spur Gears of width 5 mm operating at 1200 rpm, Stainless steel Spur Gears are >2 times stronger than their brass or plastic alternatives. A module 0.8, 25-tooth Ground steel Spur Gear of width 8 mm is >3.5 times stronger than the non-ground steel alternative. The strength of Plastic Spur Gears is approximately 10-15% as compared to Steel Spur Gears. Depending on their intended use, metal gears may be treated to further improve properties such as their hardness or corrosion-resistance.
| Material | Notes |
| Carbon steel | Carbon steel gears are made out of S45C grade steel (am C45, 1.0503). This is a high strength, medium carbon content (0.45%) steel commonly used in gears or other mechanical/structural applications. This steel can resist medium loads and heavy wear. It may be induction-hardened* for added tooth surface hardness - our hardnened S45C gears are HRC 40-45. |
| Ground steel | Ground steel gears are made from chromium-molybdenum steel (JIS G4105, which encompasses SCM 415, 420, 421, 435, 440, 822). If the gear will be subject to heavy loads and/or wear, this material might be a good choice for your application. Ground spur gears can also offer steady, accurate motion and are especially useful for mechatronic, semiconductor and mechatronic applications. For induction-hardened* ground steel gears, SCM 435 is hardened to 45-50 HRC. For case-hardened ground steel gears, SCM 415 is used. |
| Stainless steel | Our gears are usually made from 304 series stainless steel. Occasionally you might see 440C stainless steel gears as well. This material is for gears that need to be resistant to corrosion. There is more in-depth information about these grades on our stainless steels technical page. Stainless steel is more expensive than steel because it contains extra alloying elements that provide an anti-corrosion coating. |
| Brass | Brass is an alloy of copper and zinc with a golden/yellow metallic lustre. Our gears are made of leaded brass (CuZn39Pb3; architectural bronze) that has excellent machinability. It is resistant to oxidation but is not compatible with acids, amines or ammonia. |
| Plastic (thermoplastic polymer) | Our gears are available in white, black and blue polyacetal (PA - also known as polyoxymethylene; POM).** PA is thermoplastic, lightweight and cost-effective. Our blue and white PA gears are machined to JIS B 1702-1 (accuracy standard) class 9/10. The black PA gears are injection moulded to JIS B 1702-1 class 11 and are therefore lower cost. However, we also supply PA gears with brass bushings for applications which require tight hub tolerances. PA gears are less noisy than metal gears. |
*Note: Induction hardening can lower the accuracy class of the gears.
**Note: Polyacetal (PA) may swell due to fluid absorption, although to a lesser extent than nylon gears, for example. PA is not compatible with alcoholic solutions >15% or with concentrated acids. It is extremely resistant to alkaline solutions and to organic fluids, such as oils. PA is also flammable if ignited. We recommend you test the material in your intended application to ensure that the working environment (e.g. temperature, chemicals) does not affect the gear’s performance.
Spur Gear calculations
The size and material of the Spur Gear affects the maximum torque that can be transmitted between gears. The relevant calculations for allowable transfer torque for our Spur Gear range are shown in our technical pages. The relevant equations are shown in the box to the left hand side.
Example calculation: if a drive gear is operating at 200 rpm, what is the second, paired gear's speed?
To answer this question, you need to know the number of teeth each gear has. If there are differing numbers of teeth between the two gears, the one with more teeth is called the gear, and the smaller is the pinion. Let's say that the drive gear (a.k.a. the pinion) has 10 teeth and the second gear has 50 teeth.
The gear/speed ratio = 50/10 = 5
And therefore, the rotation speed of the second gear is equal to the input speed divided by the gear ratio = 200/5 = 40 rpm.
This example shows that if the drive gear has fewer teeth than the paired gear, the speed is reduced.
Example calculation: if the drive gear, which is operating at 200 rpm, is being driven by a gearbox providing 240 Watts of power, what torque is transmitted by the drive gear?
Assuming that the gearbox is 100% efficient with respect to power transfer to the drive gear in this example, using the equation shown in step 8, the torque = 9.5493 x (240/200) = 11.5 Nm.
Example calculation: given the torque transmitted by the drive gear, what is the torque transmitted by the paired gear?
In the previous example, we calculated that the drive gear transmits 11.5 Nm torque to the paired gear. In the first example, we calculated a gear ratio = 5 (50 teeth/10 teeth).
However, the gear ratio is also equal to the output torque divided by input torque. To find the output torque therefore, mutiply the input torque by the gear ratio. In this case, 11.5 x 5 = 57.5 Nm output torque.
This example shows that although the speed of the second gear is reduced compared to the drive gear, it transmits a higher torque, which can be a mechanical advantage.
Types of Spur Gears
Once you've chosen the correct module size, number of teeth required and Spur Gears material for your application, you'll need to find and order the correct gear. We hope that we have made this process as easy as possible on our website and in our catalogues, but it's worth bearing in mind that certain configurations of gear might look a little different that you first expect. We will give you an example below - these are all carbon steel module 1 gears...
This is a typical module 1 Spur Gear. This product comes with 14-120 teeth and the CAD model shows an example with two threads for set screws.
The same hubbed module 1 gear with fewer teeth might look a bit different - here is an example of an m1 gear with 8-10 teeth.
... Or, a module 1 Spur Gear with 8-10 teeth and with a smaller hub diameter would look like this!
Also note that some hubless gears have an asymmetrical hole - the gap is a 'keyway' for a keyed power transmission.
Backlash: what is it?
In the context of gears, ‘backlash’ is the amount of clearance (or ‘play’) between gears. This gap exists on the trailing face of the tooth of the driving gear and on the leading edge of the tooth behind it. Circumferential backlash is measured along the reference line. Backlash is a function of the gear module size and it also depends upon the material a gear is made from. It becomes most important when the gears must change direction, as the backlash distance must be closed before force can be transferred in the new direction.
All gears have a certain amount of backlash, but gears made to the highest accuracy standards (as ours are) have less backlash. The amount of backlash you could expect is displayed in the table below.
Material backlash table
| Module size range | Material | Backlash (mm) |
| < 0.9 | any | 0.02 - 0.06 × module size |
| 0.9 - 3.0 | stainless steel, brass, plasticcarbon steelground steel (CrMo alloy) | 0.06 - 0.12 × module size0.04 - 0.10 × module size0.04 - 0.08 × module size |
| 3.0 - 5.0 | carbon steel | 0.06 - 0.12 × module size |
Note that these values are approximations for meshing gears of the same material.
Anti-backlash Spur Gears
Backlash can be further minimised by the use of Anti-backlash Gears. Anti-backlash Gears do still allow for lubrication and thermal expansion. The main applications for anti-backlash Spur Gears are usually in processes when repeated overlays must be applied to an object precisely, or where any jerky movements upon changing gear direction may cause issues (e.g. rigs used in filming or construction).
We produce Anti-backlash Spur Gears. These Spur Gears are made of a ‘Split’ Spur Gear (split in half perpendicular to the gear axis) with the first half joined to the hub and the other half joined to the first by a spring mechanism between the two faces. The springs pull the gears together (like a pair of scissors) minimising backlash as much as possible without altering the functionality of the machinery. This provides the effect of having a gear with ‘expanding’ teeth, because the spring-loaded half of the Spur Gear fills the backlash space.
Why choose Automotion Components for Spur Gears?
We have a large range of high-quality Spur Gears in stock
Our Spur Gears are either from stock or on a short lead time. We deliver internationally from our UK warehouse. Full export documentation is always provided for overseas customers. We supply a range of hubbed and non-hubbed gears in modules 0.3-5, strengthened or weight reduced. All gears are to the relevant ISO/JIS standards.
We strive to offer a first-class customer service experience
We are a leading UK engineering components supplier with 50 years' experience. We want to make ordering from us as easy and efficient as possible for our customers. We offer free online CAD models and quantity discounts to all customers and access to a technical team to provide assistance should you need it.
Require Technical Help?
Do you require technical help? Please enter your details below and enter your queries in the comments section below. We will contact you as soon as possible.
