Mitre Gears

What is a mitre gear?

A mitre gear is a type of bevel gear used in pairs to transmit power between two shafts at a right angle, without changing speed. Both gears in a mitre pair have the same number of teeth, giving a 1:1 ratio, so the output shaft turns at exactly the same speed as the input shaft, just in a different direction. Mitre gears are the simplest way to turn a drive through 90 degrees while keeping the same speed and torque.

Mitre gears have teeth cut on a conical surface, angled at 45 degrees, so that when two identical gears mesh, their shafts meet at 90 degrees. They are supplied as matched sets of two, ready to fit to the input and output shafts.

A typical mitre gear has:

• Conical toothed face - teeth cut on a 45 degree cone, which mesh with the matching gear
• Hub or boss - the body of the gear that holds the bore, often with space for a set screw or keyway
• Bore - the hole that fits the shaft, either a plain bore or a bore ready for machining
• Back face - the flat rear face, used as a reference when setting the gear position

Mitre gears are usually described by:

• Module - the tooth size in metric gears, such as 1.0, 1.5, or 2.0 module. A larger module means larger, stronger teeth
• Number of teeth - such as 16, 18, or 20 teeth, which is the same on both gears in the pair
• Pressure angle - the angle of the tooth profile, commonly 20 degrees
• Pitch circle diameter - the effective working diameter, which for metric gears is the module multiplied by the number of teeth
• Bore - the diameter of the shaft hole
• Material - such as En8 steel, die cast zinc, or plastic

For example, a set of two 1.0 module En8 steel mitre gears with 20 teeth and a 20 degree pressure angle has a pitch circle diameter of 20 mm and turns the drive through 90 degrees at the same speed.

Key features:

• 90 degree drive - turns a drive through a right angle
• 1:1 ratio - keeps the same speed and torque on both shafts
• Matched sets - supplied as pairs of identical gears for correct meshing
• Compact - a simple way to change drive direction in a small space
• Positive drive - meshing teeth give a reliable drive with no slipping
• Range of materials - steel for strength, zinc for economical light-duty drives, and plastic for quiet running
• Machinable bores - many gears can be bored and keyed to suit the shaft

In simple terms, a mitre gear pair is two identical cone-shaped gears that turn a drive through 90 degrees without changing its speed.

Why are mitre gears essential?

Mitre gears are essential because many machines need to change the direction of a drive without changing its speed. Motors, handwheels, and drive shafts are often positioned at right angles to the parts they need to turn. Mitre gears provide a simple, compact, and reliable way to make that change, keeping both shafts turning at the same speed with the same torque.

Their main benefits are:

• Right-angle drive - changes drive direction efficiently through 90 degrees
• Equal speed - keeps input and output speeds the same
• Compact design - fits into tight spaces where other drive methods would not
• Positive drive - no slipping, giving accurate and reliable movement
• Efficient - transmits power with low losses when set up correctly
• Simple to design - straightforward to include in mechanisms and gearboxes
• Versatile - suits manual mechanisms, light drives, and heavier industrial drives

Mitre gears are used across a wide range of industries and applications, including:

• Gearboxes - right-angle gearboxes and drive units
• Machine tools - feeds, adjustments, and right-angle drives
• Packaging and food machinery - turning drives through corners on production lines
• Agricultural machinery - drives and adjustment mechanisms
• Automation and robotics - compact right-angle drives
• Hand-operated mechanisms - handwheels, adjusters, and winders
• Printing and textile machinery - drive and timing mechanisms
• Model engineering and hobby projects - small right-angle drives

The main types of mitre gears

Mitre gears are usually grouped by tooth design, material, and size.

By tooth design:

• Straight mitre gears - have straight teeth running towards the apex of the cone. They are the most common type, economical, and suitable for low to moderate speeds
• Spiral mitre gears - have curved teeth that engage gradually, giving smoother, quieter running and higher load capacity at higher speeds

By material:

• En8 steel mitre gears - made from a medium carbon steel with good strength and machinability, ideal for general engineering and medium-duty drives
• Hardened steel mitre gears - for higher loads, higher speeds, and longer life
• Die cast zinc mitre gears - economical gears for light-duty drives, mechanisms, and low loads
• Plastic mitre gears - made from acetal or nylon, giving quiet, low-friction, corrosion-resistant running for light-duty drives
• Stainless steel and brass mitre gears - for corrosive environments and specialist applications

By size:

• Small module mitre gears - such as 0.5 and 1.0 module, for light-duty and compact mechanisms
• Medium module mitre gears - such as 1.5 and 2.0 module, for general engineering
• Large module mitre gears - such as 2.5 module and above, for heavier loads

By bore:

• Plain or pilot bore gears - supplied with a bore that can be machined to suit the shaft, often with a keyway added
• Finished bore gears - supplied ready-bored, sometimes with a set screw or keyway

How to choose the right mitre gears?

Choosing the right mitre gears means matching them to the load, speed, and layout of the drive. Work through these points in order:

• Module - choose a module large enough for the load. Larger modules give stronger teeth
• Number of teeth - choose a tooth count that gives a pitch circle diameter suitable for the space and load
• Torque and speed - check the gears can handle the torque and speed of the application
• Material - choose En8 or hardened steel for strength, die cast zinc for economical light-duty drives, and plastic for quiet, low-maintenance running
• Tooth design - choose straight teeth for general use, or spiral teeth for smoother, quieter running at higher speeds
• Bore - check the bore suits your shaft, or choose a gear that can be bored and keyed to size
• Pressure angle - make sure both gears have the same pressure angle, usually 20 degrees
• Space - check the pitch circle diameter and overall size fit the available space
• Matched sets - always use mitre gears as matched pairs with the same module, tooth count, and pressure angle
• Environment - consider moisture, corrosion, and temperature when choosing the material
• Quality and brand - choose gears from reputable suppliers for accurate teeth and smooth meshing

How to fit mitre gears

Fitting mitre gears correctly is important for smooth, quiet running:

• Support the shafts rigidly - mount both shafts in bearings close to the gears to prevent flexing
• Check the shaft angle - make sure the shafts meet at exactly 90 degrees
• Set the mounting distance - position each gear along its shaft so the cone apexes meet at the same point, following the manufacturer’s mounting distance
• Set the backlash - leave a small amount of free play between the teeth to prevent binding
• Allow for thrust - mitre gears push along their shafts as they turn, so use shoulders, collars, or thrust bearings to hold them in position
• Secure the gears - fix the gears to their shafts with keys, set screws, or pins
• Lubricate - apply suitable grease or oil to steel and zinc gears. Plastic gears may need little or no lubrication
• Check the mesh - turn the gears by hand to check for smooth, even meshing without tight spots

FAQ - All you need to know about mitre gears

What is a mitre gear?

A mitre gear is a bevel gear used in matched pairs with the same number of teeth, transmitting power between shafts at 90 degrees with a 1:1 ratio.

What is the difference between a mitre gear and a bevel gear?

Mitre gears are a type of bevel gear. Mitre gears have a 1:1 ratio and change direction only, while other bevel gear pairs have different numbers of teeth to change speed and torque as well as direction.

Do mitre gears change speed?

No. Because both gears have the same number of teeth, the output turns at the same speed as the input.

What does module mean?

Module describes the size of the teeth. A larger module means larger, stronger teeth. Both gears in a pair must have the same module.

How do I work out the pitch circle diameter?

For metric gears, multiply the module by the number of teeth. For example, a 1.0 module gear with 20 teeth has a pitch circle diameter of 20 mm.

What is En8 steel?

En8 is a medium carbon steel with good strength, toughness, and machinability, widely used for gears, shafts, and engineering parts.

When should I use die cast zinc mitre gears?

Die cast zinc mitre gears are an economical choice for light-duty drives, low loads, and mechanisms such as adjusters and handwheels. Use steel gears for higher loads.

Can I mix mitre gears from different sets?

It is best to use matched sets. Both gears must have the same module, tooth count, and pressure angle, and mixing gears from different sources can cause poor meshing and wear.

Do mitre gears create thrust loads?

Yes. Mitre gears push along their shafts as they turn, so they need shoulders, collars, or thrust bearings to hold them in position.

Do mitre gears need lubrication?

Steel and zinc mitre gears should be lubricated with suitable grease or oil to reduce wear and noise. Plastic mitre gears can often run with little or no lubrication.

Why are my mitre gears noisy or wearing quickly?

Common causes include incorrect mounting distance, too little or too much backlash, misaligned or flexing shafts, overloading, or lack of lubrication. Check the setup and replace worn gears as a pair.