Connecting Shafts of 2 Very Different Diameters

  • Thread starter Steven123456789
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In summary, there are a few options for connecting a motor with a 4 mm diameter shaft to a steel rod with a 30 mm diameter. These include using a machine shop to create a custom coupling, using belt and pulleys, or using bead chain if low torque is needed. Other factors to consider include the support and balance of the 30 mm bar, the maximum operating RPM of the motor and bar, and the mounting and alignment of the motor. Depending on the torque needed, various methods such as rubber wheel against a friction band, a flexible joint, or a centre-tap bar with a part-threaded bolt can be used.
  • #1
Steven123456789
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I want to ask, if I want to connect a shaft from a motor that only has a diameter of 4 mm to a steel rod with a diameter of 30 mm, what should I do so that the motor can rotate the steel rod?
 
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  • #2
Either a machine shop or belt and pulleys. :wink:
(I suppose if you need very low torque you could use bead chain instead of a belt, but the appropriate pulleys are somewhat scarce.)
 
  • #3
Steven123456789 said:
a motor that only has a diameter of 4 mm to a steel rod with a diameter of 30 mm
What that enormous size mismatch is telling me, is that likely there are other under- or overdesigns there somewhere. Could you please share more about that ... machinery?
 
  • #4
Welcome to PF.

How you couple the shafts will depend on how the 30 mm diameter bar is supported, on a frame by one or more bearings, of what type?

Is it balanced?
What is the maximum operating rpm of the motor and bar?

How is the motor mounted to the frame?
Can it self-align with the 30 mm bar?
Or must the coupling be flexible?

How much torque will the motor be providing?
Or what is the 30 mm bar being used for?
 
  • #5
Baluncore said:
Welcome to PF.

How you couple the shafts will depend on how the 30 mm diameter bar is supported, on a frame by one or more bearings, of what type?

Is it balanced?
What is the maximum operating rpm of the motor and bar?

How is the motor mounted to the frame?
Can it self-align with the 30 mm bar?
Or must the coupling be flexible?

How much torque will the motor be providing?
Or what is the 30 mm bar being used for?
2 bearings, ID 30 mm x OD 37 mm x width 4 mm
Torque the motor providing - 0.4 N cm
the 30 mm bar will be used to rotate the mechanism
 
  • #6
What is the maximum RPM?
 
  • #7
If low torque, classic trick is to spring-mount motor with small rubber wheel directly against friction band on cylinder. Like electric-assist bikes did before hub motors....

Plan_B is to machine end of bar down to compatible size, connect motor shaft via 'universal' or flexible joint.

If only needs to rotate in one direction, perhaps centre-tap bar, saw the head off compatible part-threaded bolt and connect that to motor shaft via 'universal' or flexible joint.
 

FAQ: Connecting Shafts of 2 Very Different Diameters

What is the best method to connect two shafts of significantly different diameters?

The best method to connect two shafts of significantly different diameters is to use a flexible coupling or an adapter sleeve. Flexible couplings can accommodate misalignment and varying diameters, while adapter sleeves can provide a seamless transition between different shaft sizes.

How do I ensure the connection between different diameter shafts is secure?

To ensure a secure connection between shafts of different diameters, it is essential to use precision-machined components and appropriate fasteners. Keyed joints, set screws, or clamping mechanisms can provide additional security. Additionally, proper alignment and torque specifications must be followed during installation.

What are the potential issues when connecting shafts of very different diameters?

Potential issues include misalignment, imbalance, and stress concentration. Misalignment can lead to excessive wear and vibration, while imbalance can cause operational inefficiencies. Stress concentration at the connection point can result in premature failure if not properly managed.

Can I use a bushing to connect shafts of different diameters?

Yes, a bushing can be used to connect shafts of different diameters. Bushings can fill the gap between the shafts, providing a snug fit and reducing the risk of misalignment. They are particularly useful when the difference in diameter is not too large.

What materials are recommended for connecting shafts of different diameters?

The choice of materials depends on the application and operating conditions. Common materials include steel, aluminum, and various alloys. For high-torque or high-stress applications, hardened steel or specialized alloys may be required. It is also important to consider corrosion resistance and thermal expansion properties.

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