Coupling is a core component that transmits power and motion
from the driving shaft to the driven part while absorbing misalignment
and any possible factors that could reduce efficiency of machines
(e.g. vibration, noise, electric current, etc.)

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  • Why Couplings?
  • Installation Guide
  • Selection Guide
  • Customer-friendly Services
  • Environmental Compliance
  • Made-To-Order Process
  • Varieties for Special Environments
  • Balancing Correction

Coupling Selection Guide

  1. STEP 1 Select a
    coupling type

    A coupling type is selected mainly according to characteristic chart and types of connected motors. In case it is going to be used in a special environment e.g. vacuum, high-temperature, cleanroom facilities etc., please contact Sung-il Customer Service team in advance. As Sung-il Machinery manufactures products with various types of material, we may suggest an appropriate coupling considering the circumstance it is to be used.

  2. STEP 2 Select a
    outer diameter
    (OD) size

    The coupling’s outer diameter (OD) size is determined mainly by torque. The rated torque of a coupling has to be higher than the operation torque of a motor. The safety factor could be differently calculated by case/customer. The operation torque information can be easily found on the motor’s specification.

    In case the operation torque should be calculated with operational P(Power Output) and N(rpm) values, please refer to the below formula.

    T = 9550 x P(kW) N(rpm)

    In case a coupling includes plastic sort material (SHR, SJC, SOH, SFC series), the rated torque of a coupling has to be modified according to temperature ranges. Please refer to the below table.

    Temperature range -20 ℃ ~ 30 ℃ 30 ℃ ~ 40 ℃ 40 ℃ ~ 60 ℃ 60 ℃ ~ 120 ℃
    Correction factor 1.0 0.8 0.7 0.55
  3. STEP 3 Check the max. inner diameter (ID)

    Both inner diameters (ID) of driving and driven shafts have to be within the range of maximum ID of a coupling. If either ID of driving shaft or driven shaft is out of range from the selected coupling, the coupling has to be sized up. For instance, SDS-19C is selected at the Step 2, however the ID of shaft is 8mm, it is out of range as the max. ID on SDS-19C is 6mm. In this case, the coupling should be one sized up to SDS-22C.

    Model Standard Inner Diameter (d1, d2) (mm)
    3 4 4.5 5 6 6.35 7 8 9 9.525 10 11 12 12.7 14 15
    SDS-22C ●★ ●★
    In the table above, highlight the row of model name SDS-19C In the table above, highlight the row of model name SDS-22C In the table above, highlight the column to which 'Standard Internal 8' belongs

    However, the coupling size cannot be adjusted due to space matter, please check with us for the alternative option of non-standard ID supply by re-boring ID sizes over the range. In this inevitable case, re-boring inner diameters itself may not be so difficult, however there is high possibility that the durability of product drops down to a greater extent thus, this process is only implemented under customer’s full responsibility. Besides, the lead-time could be somewhat longer than usual.

  4. STEP 4 Check
    slip torque

    ‘Slip Torque of selected ID(shaft)’ > ‘Operating torque’

    Please compare slip torque values of each selected inner diameters with the operational torque referring to the information in the “Dimensions / Performance” pages. (See the example table below.)

    Let’s suppose the coupling SDS-22C-4mmx8mm is selected through step.1 to step.3. According to the slip torque table, the max. torque of SDS-22C is 2.2N·m. The slip torque at the ID 8mm is higher than 2.2N·m (The specific slip torque values higher than the max. torque of couplings are not stated in the table.) and at the ID 4mm 1.4N·m respectively. Since the slip torque at the ID 8mm is higher than max. torque of the coupling, there is no further concern about slips at the ID 8mm. However, the slip torque at the ID 4mm must be compared with the operating torque, concerning its slip torque(1.4N·m) is lower than the max. torque of the coupling. In any case the slip torque is lower than the operating torque like this, a larger sized coupling must be selected or an additional supplement e.g. key/keyway has to be along with for safer use.

    The slip torque values may be subject to change according to different testing conditions. (e.g. shaft tolerance, surface roughness, or acceleration/deceleration of driving shafts)

    Model Max.
    Slip Torque (N.m) by Inner Diameter (d1, d2)
    3 4 4.5 5 6 6.35 7 8 9 9.525 10 11 12 12.7 14 15 15.875 16
    SD□□-16C 1 0.6 0.7 0.8 0.9
    SD□□-19C 1.8 1 1.3 1.4 1.5 1.7
    SD□□-22C 2.2 1.1 1.4 1.5 1.7 2 2.1
    SD□□-26C 3 2 2 2.9
    Highlight the maximum torque value (2.2) of the model name SDS-22C in the table above. Highlight 'Slip Torque 4 Values by Internal' (1.4) of the model name SDS-22C in the table above. Highlight 'Slip Torque 8 Values by Internal' (None) of the model name SDS-22C in the table above.
  5. STEP 5 Check other points

    Clamping Methods, Permissible misalignment, Torsional stiffness, Max. rpm, etc.

※ Clamping Methods by coupling types

Coupling types
High performance Rubber Disk High Torque Disk Jaw Oldham Radial Beam Rigid Cross Joint Urethane Flexible
Clamping Methods Set-screw
(No mark)
General X O X O O O O O
With Keyway X O X O O O O O O O X
General O O O O O O O O O O X
Hub Split O O X X O X X
With Keyway O O O O O O O O O O X
Taper-ring (T) X X X X X X X X X X
insertion (I)

※ △ symbol in the above table means that the availability is subject to differ according to each outer diameter size.

Set-screw Type
How to work
Clamp a coupling onto a shaft only by screw’s thrust, contacting screws directly to the shaft
Economical and Simple
Less clamping force
The surface of shaft can be damaged due to direct contact
Key & Keyway Type
How to work
Clamp a coupling onto a shaft by interlocking a key and keyway each other
Better clamping force unless the key or the coupling hub is broken.
Can be used as a complementary option for Set-screw or Side-clamp methods
Keyway can be worn out easily under repeated rotation.
Relatively complicated to install
Side-clamp Type
How to work
Clamp a coupling with fastening screws in a vertical way to the shaft and make the coupling’s inner diameter contracted by the side-slits
Better clamping force than the Set-screw type
Easy and simple to install
Unless the tolerances are well-managed, the clamping force is not always guaranteed
Side-clamp Hub Split Type
How to work
A part of coupling’s hub can be completely split off. (The working process is as same as the general Side-clamp Type)
No need of shifting the connected devices during maintenance.
Better clamping force than the general Side-clamp Type
Higher cost due to the additional processing
Taper-ring Type
How to work
Clamp a coupling onto a shaft by interlocking screws on the wedge-shaped inner and outer rings
High clamping force with self-centering function
The excellent structure for self-balancing feature
Relatively higher cost
Relatively complicated to install
Shaft-insertion Type
How to work
Bushing and Insert hub are tightly coupled by the thrust of fastening screws. And then the insert part gets spread outward due to the taper structure and clamped into the inner diameter on the other side.
Space-saving design
Simple clamping methods by tightening a single screw
1/10 Taper Bushing Type
How to work
Ideal when a motor’s shaft is taper-shaped
A simple application using bushings. (without having to additionally shape the coupling’s inner diameter as taper ring)