Tapered Bore Pulleys

What are tapered bore pulleys?

Tapered bore pulleys are pulleys with a cone-shaped bore, designed to be fitted to a shaft using a separate taper bush. The taper bush is bored to the shaft size and slides into the pulley. When its screws are tightened, the bush is drawn into the tapered bore and squeezes tightly onto the shaft, gripping it firmly without the need for any machining. This makes tapered bore pulleys one of the quickest and most practical ways to fit a pulley to a shaft, and they are used on V-belt and timing belt drives across industry.

A standard tapered bore pulley is made up of:

• A pulley body with grooves or teeth around the rim, to suit the belt
• A tapered bore in the hub, machined to suit one size of taper bush
• Half-threaded holes in the bore, which line up with holes in the bush for the fixing screws
• Flanges on some timing pulleys, to keep the belt in place.

The taper bush is supplied separately.

• The bush has a parallel bore and keyway to suit the shaft, and a tapered outside that matches the pulley.
• Because bushes are made in many bore sizes, one pulley can be fitted to a range of shafts simply by choosing a different bush.

Tapered bore pulleys are described by their belt type, size, number of grooves or teeth, and the taper bush size they take.

Why are tapered bore pulleys essential?

Tapered bore pulleys save time and cost. There is no need to bore, key, or ream the pulley, as all the shaft fitting is done by the bush. The pulley can be fitted on site with basic hand tools, and removed easily for maintenance without damaging the shaft.

The taper creates a tight, even grip around the shaft, which reduces wear, fretting, and wobble compared with set screws alone. Taper bushes are also an interchangeable standard, so pulleys, sprockets, and couplings from different suppliers can share the same bushes.

Typical applications include:

• Electric motor and gearbox drives
• Fans, blowers, and air handling units
• Pumps and compressors
• Conveyors and material handling equipment
• Agricultural and processing machinery
• Machine tools and woodworking machinery
• Automation and packaging machinery
• Drives that are changed or maintained regularly

The main types of tapered bore pulleys

• Tapered bore V-belt pulleys - Pulleys with V-shaped grooves for wedge belts, such as SPZ, SPA, SPB, and SPC, or classical belts. Available with one or more grooves.
• Tapered bore timing pulleys - Pulleys with teeth to suit timing belts, in metric and imperial profiles, such as 5M, 8M, 14M, L, and H.
• Flanged and unflanged pulleys - Timing pulleys are often supplied with flanges to keep the belt in place. V-belt pulleys do not need flanges.
• Cast iron pulleys - The most common material for larger pulleys, as cast iron is strong, stable, and damps vibration.
• Steel and aluminium pulleys - Smaller pulleys may be made from steel or aluminium, which are lighter and suit smaller, faster drives.

How to choose the right tapered bore pulleys?

• Belt type and size - Choose a pulley to match the belt exactly, whether it is a V-belt section or a timing belt profile and pitch.
• Diameter or teeth - Choose the pitch diameter or number of teeth to give the speed ratio needed.
• Grooves or width - Choose enough grooves for the number of V-belts, or enough width for the timing belt.
• Taper bush size - Check the bush size the pulley takes, and that the bush is available in your shaft size. Each bush size has a maximum bore.
• Bush order - Remember the taper bush is not normally included with the pulley, and must be ordered separately to suit the shaft.

Essential references and specialised ranges

How the numbering works:

Taper bush sizes are given as four digits. The first two show the bush’s outside size, and the last two show its length, both in tenths of an inch. For example:

1108 = around 1.1 inches across and 0.8 inches long, maximum bore 28mm

1210 = around 1.2 inches across and 1.0 inches long, maximum bore 32mm

1610 = around 1.6 inches across and 1.0 inches long, maximum bore 42mm

2012 = around 2.0 inches across and 1.2 inches long, maximum bore 50mm

2517 = around 2.5 inches across and 1.7 inches long, maximum bore 65mm

Pulley references usually show the belt and size, and the bush size is listed in the product details. For example:

SPZ63-1-1108 = SPZ V-belt pulley, 63mm pitch diameter, 1 groove, takes a 1108 bush

19-H-100F = timing pulley with 19 teeth, H pitch, for a 1 inch wide belt, with flanges

Suffixes:

F = flanged

TB = taper bore

Suffix codes vary between manufacturers, so check the supplier’s catalogue for the exact meaning.

FAQ - All you need to know about tapered bore pulleys

Is the taper bush included with the pulley?

Usually not. The bush is ordered separately, in the bore size that suits your shaft. Check the pulley’s product details for the bush size it takes.

Do I need a key with a taper bush?

In most cases, yes. The taper gives a strong grip, but a key in the shaft and bush is recommended to stop the pulley slipping under load.

How do I fit a tapered bore pulley?

Clean the bore and bush, fit the bush into the pulley with the screw holes lined up, and slide it onto the shaft. Tighten the screws a little at a time, in turn, to the recommended torque. Tap the bush face lightly with a soft mallet and tighten again.

How do I remove a tapered bore pulley?

Remove the fixing screws, then fit one into the removal hole, which is threaded only in the bush. Tightening this screw pushes the bush out of the taper and releases the pulley.

Can I use a taper bush from another supplier?

Yes. Taper bushes are made to a common standard, so bushes of the same size are usually interchangeable between brands.

How do I identify the pulley I need?

Check the code on the pulley or in the machine’s parts list. If it cannot be read, identify the belt type, measure the diameter or count the teeth, count the grooves, and check the bush size stamped on the bush face.

How can I tell if a tapered bore pulley needs replacing?

Warning signs include:

• Worn grooves or teeth
• The pulley moving or slipping on the shaft
• A damaged or worn tapered bore
• Cracks in the hub or rim
• Rapid belt wear, slipping, or noise
• Vibration or wobble when the drive is running