taper-bush

Technical Knowledge

QD bushings are identified by lettered families rather than the numbered Taper Lock series. That naming system is useful because the letter fixes the outside flange/barrel geometry; the shaft bore and keyway are then selected within the family. For replacement, both pieces of information matter.

The table below is a quick dimensional reference for EP-SF through EP-S standard QD family sizes. Use it with the drawing, because bolt circle, cap-screw arrangement, bore range and standard/shallow keyway options are also part of the interface.

QD designation system

The QD sequence progresses through lettered sizes as the bushing grows. The steel QD range includes EP-SF, EP-E, EP-F, EP-J, EP-M and EP-N; larger standard-family references include EP-P, EP-W and EP-S. The model letter identifies the mating hub family, not a single shaft diameter.

SF to S dimension reference

Bore range and keyway options

The QD technical sheet includes stock-bore ranges and distinguishes standard and shallow keyway configurations. When an old QD bushing is being replaced, record the letter family, bore, keyway type and mating sheave/sprocket. A bushing with the correct bore but the wrong QD family will not match the outside hub geometry.

Plain bore and stainless options

The technical data also includes plain-bore/not-split references and notes that stainless-steel QD bushings can be made to order. Treat these as separate configurations that need explicit RFQ details; do not assume a standard split steel QD bushing and a special plain or stainless version share every feature.

Selecting the right QD series

For replacement, identify the installed QD family first from marking, flange dimensions and bolt circle, then match the shaft bore/keyway. For a new fabricated component, choose the QD size with the hub or weld-on hub design, then make sure the shaft and duty can be supported by the complete assembly.

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Technical Knowledge

Metric-bore taper bushings are common in machines designed around millimetre shaft sizes, but “metric bore” is only the first part of the specification. The keyway convention, shaft tolerance, mating hub and exact bushing series still have to agree. A 40 mm shaft in a DIN-designed gearbox may not use the same key geometry as an imported machine with a different standard.

The EP technical tables include metric keyway dimensions tied to DIN 6885 and JIS B 1301-1976 references and show an ISO-style centerline method for measuring keyseat depth. That information is useful when converting an old inch-based maintenance record into a precise metric RFQ.

Where metric bores appear

Metric bores are relevant in European, Japanese and many globally supplied machines. They also appear in replacement work where an inch-family bushing is machined or stocked with a metric shaft bore. Do not let the product family name decide the units; read the actual bore marking or measure the shaft.

DIN 6885 and JIS keyway references

Understanding centerline keyseat depth

The metric drawing expresses keyseat depth with reference to the bore centerline. That is different from casually measuring down from the surface of a bore with a caliper. When checking an unknown part, measure the key width and the shaft/keyseat geometry and compare them with the chosen standard rather than relying on one depth measurement.

Nominal bore is not the whole fit specification

A nominal 50 mm bore tells you the target shaft size, not every tolerance or surface-condition requirement. Inspect the shaft for wear, plating, corrosion or repair work that may have changed its effective diameter. If the machine drawing calls out a shaft fit or tolerance class, include that information in the enquiry rather than asking for “50 mm” alone.

Ordering a metric bore from EVER POWER

Send the EP series or existing marking, shaft diameter in mm, required keyway standard, mating hub or pulley reference and a drawing when available. If the original machine uses a non-standard key or multiple keys, provide the actual dimensions instead of forcing the requirement into a DIN label.

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Technical Knowledge

A taper lock bushing turns a small amount of axial screw movement into a strong radial connection between a shaft and a pulley, sprocket, sheave or hub. The mechanism is compact because the bushing and mating component share a shallow taper; as the fasteners draw the parts together, the bushing grips the shaft around its circumference.

The EP drawings use an 8-degree taper reference and separate tightening/removal-hole functions. That geometry explains why installation needs even staged tightening and why removal is performed with the designated jack positions rather than by simply pulling on the hub.

The basic geometry of the taper

Picture two matching conical surfaces. Moving one axially into the other reduces the available radial clearance. In a taper-bushing assembly, screw force provides the axial motion, the taper converts that motion into radial pressure, and the split in the bushing allows the bore to clamp onto the shaft.

A shallow taper can maintain a strong mechanical grip after tightening, but the connection still depends on clean surfaces, correct dimensions and undamaged fasteners. The taper angle is not a substitute for checking the actual model and hub.

Three parts work together

How force is transferred to the shaft

As the fasteners are tightened, radial contact pressure develops between the bushing bore and shaft. Friction contributes to torque transfer, while a key and keyway can provide an additional positive mechanical path where the design uses one. The load path is therefore distributed around the connection rather than concentrated at a single setscrew point.

That does not mean every taper bushing can transmit any torque. Capacity depends on the actual bushing, shaft, hub, keyway, fasteners, material and operating duty. Use model-specific technical information when sizing a new drive.

Why installation and removal use different holes

The threaded-hole arrangement lets the same basic fastener system perform two opposite jobs. In the tightening positions, the screws pull the bushing and hub together. In the removal positions, they act as jacks and force the taper apart. Mixing these functions is a common reason an assembly will not seat or release as expected.

How it differs from other shaft connections

Compared with a simple setscrew hub, a taper bushing spreads clamping action around the shaft. Compared with a permanent interference fit, it is intended to be removed using its screw arrangement. Compared with other split-clamp or QD systems, however, the outside interface is unique; the families cannot be substituted without a matching hub.

For another general terminology reference, see taper lock bushing information at taperlockbushing.com. For EP selection, start with the model code and dimensional data, then confirm bore, keyway and mating hub before ordering.

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Technical Knowledge

A size chart is most useful when it helps identify a real part, not when it is treated as a substitute for the full drawing. For EP taper-lock bushings, the A, B and D dimensions narrow the series, while the shaft bore, keyway and fastener arrangement complete the identification.

Several neighbouring models share the same A and D values but use a different B width. That is why an EP-2012 and EP-2017 can look nearly identical in a photograph yet still require different axial space and model identification.

How to read the EP model and dimensional table

Use the stamped model when it is readable. If the marking has worn away, measure A, B and D at undamaged surfaces, record the fastener size and then check the shaft bore/keyway. Do not infer bore from the model suffix alone; stock and custom bore configurations need to be verified separately.

EP-1008 to EP-5050 dimensions

Large series beyond EP-5050

How to select the correct series for a shaft

Start with the actual shaft diameter and the mating component. The bushing outside taper must match the hub, and the required shaft bore must be available or specified for that series. If you are designing a new hub, the model can be selected around shaft size and duty; if you are replacing a part, the existing hub usually fixes the family first.

For a worn or unknown bushing, send the measured A/B/D dimensions, shaft diameter, keyway, screw size and photographs. That information is more reliable than trying to identify the part from outside diameter alone.

Use the drawing with the table

The table gives quick dimensions, but the technical drawing shows which surfaces the letters refer to and where tightening/removal holes are located. On larger series, also check screw quantity and handling space around the hub.

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Technical Knowledge

A bushing can have the correct outside taper and still be wrong for the shaft if the keyway standard is mismatched. That is why global replacement work needs more than a model number: the shaft diameter, key/keyway dimensions and the convention used on the original machine must be confirmed together.

The EP taper-bushing technical data includes metric keyway references tied to DIN 6885 and JIS B 1301-1976, and it also includes a USAS B17.1-1967 keyway table. British-origin equipment may use BS 46 conventions. These references should be treated as dimensional systems, not as blanket product-certification claims.

What the keyway does

The key transfers torque through matching slots in the shaft and bushing or hub. Width, depth and fit determine whether the key seats properly. If the key is too high, it can prevent the bushing bore from gripping as intended; if it is too loose or too shallow, load can concentrate and hammer the keyway.

Four standards you may encounter

Metric keyseat depth is measured differently

The metric drawing notes an ISO-style method in which keyseat depth is referenced at the bore centerline. That is a useful reminder that a dimension labelled “depth” may not be directly comparable across different drafting systems. When reverse-engineering a worn bushing, measure the key itself and the shaft keyseat as well as the bushing bore.

Standard vs shallow keyway in QD bushings

The QD technical sheet shows standard and shallow keyway options for different bores. A shallow keyway is not simply a machining tolerance variation; it is a distinct configuration that must match the shaft/key arrangement. Include “standard” or “shallow” in the RFQ when the existing QD part is being replaced.

How to specify the keyway when ordering

A useful RFQ line is concise: “EP-2517, 45 mm bore, DIN 6885 keyway” or “EP-J-STL, 2 in bore, standard USAS/ASME keyway,” followed by a drawing when the machine is unusual. If you do not know the standard, send the shaft diameter plus measured key width and depth instead of guessing from country of origin.

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