Why might two gearboxes with the same output speed not be interchangeable?

Category: Gearbox Selection and Use · 13. question

Two gearboxes may show the same ratio (e.g. 1/30) and the same output speed on their nameplates, but if one is a small frame and the other a large one, the torque they carry is very different. Before replacing, compare these features:

Feature	Why it matters
Frame size and rated output torque	A smaller frame carries less torque at the same speed.
Gearbox type and efficiency	With the same motor, worm and helical gearboxes give different torque.
Permissible radial load	Decisive if a pulley or sprocket is fitted to the output shaft.
Output shaft	Solid or hollow shaft, diameter and key size must suit the machine.
Output direction and fixing	Right-angle or in-line; feet, flange or torque arm.
Input flange	Must fit the motor's IEC frame and B5/B14 flange.
Mounting position	Oil quantity and plug positions are set by position.

When replacing an old gearbox, sending its nameplate type, frame and ratio together with the motor nameplate and the output shaft dimensions speeds up a correct match.

Send the motor power, speed, mounting type and quantity on WhatsApp. If you are replacing an existing motor, you can also send a photo of its nameplate.

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Other questions on this topic

1. Should I choose a worm gearbox or a helical gearbox?
2. What is the difference between bevel-helical, foot-mounted helical and parallel-shaft gearboxes?
3. Should I buy the gearbox together with the electric motor, or can I use my existing one?
4. Does a worm gearbox hold the load by itself, can it replace a brake?
5. How do I choose the gearbox ratio?
6. What happens to the output speed if I fit a 1,000 rpm electric motor to the same gearbox?
7. What can be done if the output speed I need does not match the standard ratios?
8. How do I find the gearbox ratio from a conveyor belt speed?
9. How is gearbox output torque calculated?
10. What is the service factor of a gearbox and why does it matter?
11. What electric motor power can be fitted to a gearbox?
12. Is it a problem to fit a more powerful electric motor to a gearbox?
13. Why might two gearboxes with the same output speed not be interchangeable?
14. How do I check the IEC flange match between electric motor and gearbox?
15. What do radial and axial load mean on a gearbox?
16. Why does the mounting position affect the gearbox oil level?
17. When are a hollow-shaft gearbox and a torque arm used?
18. What oil goes into a gearbox, and when should it be changed?
19. What should be checked if a gearbox is leaking oil?
20. Why is my gearbox noisy?
21. Why does a gearbox get hot, and when is it a problem?

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