Belt Driven Spindle: Calculating Power & Choosing Speed/Diameter

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In summary, the conversation discusses choosing the constant speed of the counter shaft and the diameter of the spindle shaft in relation to the required power and various speeds (rpm) of the spindle. The speed of the spindle and counter shaft are related by the ratio of the pulley diameters, and there is no "right" answer for the countershaft rpm. The diameter of the spindle and/or countershaft does not affect the RPM, but they should be strong enough to handle the torque. The maximum torque can be calculated using the power and RPM, and there are tables available for typical shaft diameters.
  • #1
Tekneek
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-Lineshaft_drive_to_lathe,_with_stepped_pulleys_for_variable_speed_(Carpentry_and_Joinery,_1925).jpg

The system is similar to above. Say I have calculated the required power at the spindle and various speeds (rpm) the spindle needs to run at. I am not sure on how to choose the constant speed of the counter shaft. For the motor HP i am thinking it is just Pmotor = Pspindle/Efficiency.
Also not sure how I should go on about choosing the spindle shaft diameter.
 
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  • #2
Tekneek said:
Say I have calculated the required power at the spindle and various speeds (rpm) the spindle needs to run at. I am not sure on how to choose the constant speed of the counter shaft.

I'm not sure I understand your question. The speed (rpm) of the spindle and counter shaft are related by the ratio of the pulley diameters...

Spindle RPM / Countershaft RPM = Countershaft Pulley Diameter / Spindle Pulley Diameter

The example in the picture is..

563/800 = 4.75" / 6.75" = 0.704

There is no "right" answer for the countershaft rpm. Pulleys are only available in certain standard sizes so the problem is one of finding a motor (with suitable rated RPM) and combination of pulleys that give the right answer for the spindle rpm(s). Perhaps start with a pulley catalogue and set up a spreadsheet?

For the motor HP i am thinking it is just Pmotor = Pspindle/Efficiency.

Correct.
 
  • #3
CWatters said:
I'm not sure I understand your question. The speed (rpm) of the spindle and counter shaft are related by the ratio of the pulley diameters...

Spindle RPM / Countershaft RPM = Countershaft Pulley Diameter / Spindle Pulley Diameter

The example in the picture is..

563/800 = 4.75" / 6.75" = 0.704

There is no "right" answer for the countershaft rpm. Pulleys are only available in certain standard sizes so the problem is one of finding a motor (with suitable rated RPM) and combination of pulleys that give the right answer for the spindle rpm(s). Perhaps start with a pulley catalogue and set up a spreadsheet?
Correct.
But how would I choose the spindle diameter? I understand that I can change the pulley diameters to get the desired rpm for the spindle. But wouldn't the inner diameter of the pulley depend on how big or small the spindle shaft diameter is?
 
  • #4
Tekneek said:
But how would I choose the spindle diameter? I understand that I can change the pulley diameters to get the desired rpm for the spindle. But wouldn't the inner diameter of the pulley depend on how big or small the spindle shaft diameter is?

The diameter of the spindle and/or countershaft don't effect the RPM. They only have to be strong enough to handle the torque. It's normal to oversize so that the shaft can handle the twice the maximum torque of the motor. If you know the max power then...

Power (Watts) = Torque (Newton Meters) * Angular Velocity (Rads/S)

Angular Velocity can be calculated from the RPM.

or if you prefer

Power (HP) = Torque (pound-feet) * RPM/5252

Once you have the max torque (with a safety factor) there are tables for typical shaft diameters...

http://joycedayton.com/products/system-accessories/shafting/shafting-diameter-chart

or you can work out the diameter based on the material and the max allowed stress but that's beyond my experience.
 

Related to Belt Driven Spindle: Calculating Power & Choosing Speed/Diameter

1. How do you calculate the power of a belt-driven spindle?

The power of a belt-driven spindle can be calculated by multiplying the torque of the spindle by its rotational speed. This can be represented by the equation P = T x ω, where P is power in watts, T is torque in newton meters, and ω is rotational speed in radians per second.

2. What factors should be considered when choosing the speed and diameter of a belt-driven spindle?

When choosing the speed and diameter of a belt-driven spindle, factors such as the material being machined, cutting tool requirements, and desired surface finish should be taken into account. The horsepower of the spindle motor and the type of belt drive system being used should also be considered.

3. What is the purpose of a pulley system in a belt-driven spindle?

The pulley system in a belt-driven spindle is used to transfer power from the motor to the spindle. It also allows for different speed and torque options by changing the size of the pulleys.

4. How does belt tension affect the performance of a belt-driven spindle?

Belt tension plays a crucial role in the performance of a belt-driven spindle. Too much tension can cause excessive wear on the belt and bearings, while too little tension can result in slippage and decreased power transmission.

5. What are the advantages of using a belt-driven spindle over other types of spindles?

One advantage of a belt-driven spindle is that it allows for a wider range of speed and torque options. It is also more cost-effective and easier to maintain compared to other types of spindles. Additionally, the pulley system provides a smooth and quiet operation.

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