Spindle Speed on a Manual Mill
Let’s look at spindle speed on a manual mill as different modes of transport.
Spindle Speed on a Manual Mill is Like a Bike or Moped
The most basic mode is the 16-speed step pulley system to vary the spindle speed. This system uses different size pulleys that change the belt from one pulley to another, changing the spindle speed. This method is analogous to a 10-speed bicycle.
With a mechanical variable speed system, spindle speed is changed by mechanical pulleys. Think of this system as a bike with miniature motor on it.
The most advanced system is electronic variable speed where spindle speed changes are controlled by an inverter drive system. Electronic variable speed on a manual mill can be compared to a moped, more advanced than a 10-speed or motorized bicycle.
16-Speed Step Pulley System Like a 10-Speed
When looking at the 16-speed step pulley system, think of the bicycle chain on a 10-speed. The front sprocket has five speeds with a high and low setting and the back chain has five more with a similar high and low setting.
Similarly, a 16-speed step pulley system has eight different speed configurations and the motor is two-speed with a high and low setting. You change the spindle speed on the manual mill by taking the belts and moving them to a different pulley system.
With a mechanical variable speed system, you are still on a bike, but it’s equipped with a small motor. You trek from point A to point B faster. With mechanical variable speed, you turn a knob on the spindle, adjusting the tightness in the belt and changing the diameter of the pulleys. This varying gear ratio changes the speed on the spindle motor.
Electronic Variable Speed is the Fastest Transport
The electronic variable speed system is like a moped, the fastest mode of transport compared to a 10-speed or motorized bicycle. With electronic variable speed, you changed speed with an inverter duty motor and drive.
With an an electronic variable speed system, you can adjust your spindle speed to the optimal range of RPM’s that your tooling or metal requires. With a 16-speed step pulley system, you can cut at 100, 200 or 300 RPM’s. With electronic variable speed, you can arrange your spindle speed anywhere in this range from 1-300 RPM’s (in this example).
For example, you’re cutting 41/30 steel, using a carbide bit. You’ve used a machinist calculator and determined your optimal speed to be 298 RPM’s. You then turn the potentiometer on your manual mill to achieve this spindle speed.
Picking the Right Manual Mill Depends on your Budget
Which system is most beneficial? This depends on your budget. Electronic variable speed on a manual mill is more costly but, by far, the simplest design and easiest to use.
The 16-speed step pulley system (again, using the bicycle analogy) lacks a derailleur to change gears. You have to get off your bike and manually lift the chain from one gear to another. Likewise, with a 16-speed step pulley system, you need to power off the manual mill, open up the side of the machine, remove the belt and move it to a different pulley location.
Regarding variable speed, the drive system on an electronic model has fewer components and is more simple. A fixed drive pulley on a mechanical variable speed model requires an array of different tensioners to vary spindle speed.
EVS Equals More Torque & Less Wear
There are also ramifications with torque and part maintenance when looking at variable speed whether it is mechanical or electronic. There is less belt slippage with an electronic system than a mechanical model. Belt slippage reduces power and torque and creates more wear on the belt itself.
In conclusion, all three systems will get you where you want to go. It comes down to how much you want to spend to see how fast the 16-speed step pulley, mechanical variable speed or electronic variable speed systems will get you to your final destination.
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