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Spindles and VFD’s

February 19th, 2012 | Posted by Joshua in Spindles and Routers

Spindles and Variable Frequency Drives (VFD) are commonly seen on bigger budget CNC machines. However recently spindles and VFD’s have become increasingly affordable. Spindles are finely tuned tool’s that have immense power, an impressive speed range and are very sturdy and precise.

A Variable Frequency Drive is a speed controller for AC (Alternating Current) motors. The VFD controls the speed of the motor by changing the frequency of the electrical power going to the motor.

Spindles and VFD’s come in a range of sizes from small set up’s for smaller CNC machines and up to extremely large 3 phase systems for much bigger machines.

So now I’ll talk a bit about Spindles and VFD’s:

 

Spindles

Spindles come in a huge variety of sizes and power ratings. You can easily find tiny 1 phase spindles with a 0.8kW rating up to massive 3 phase 10kW units.

The main reasons people will choose a spindle is their ready and excellent range of collets for different diameter tooling, huge power for their size and are precision made and can hold great tolerances while cutting.

As far as cooling goes you will find fan and water-cooled versions. Fan cooled units will use a fan to pull air through the motor while it’s operating. The downside to fan cooling is that the spindle will not perform well under low-speed conditions, as the fan moves with the shaft of the motor. So if the spindle goes slow, so will the motor. Running the fan at low-speed wouldn’t move enough air to cool the spindle and would cause the spindle to over heat and destroy itself.

Water cooled versions however can be run at very low speed’s due to the water cooling being independent of the spindle. So no matter what speed the spindle is running a constant flow of water will keep the spindle cool.

Spindles have one electrical connector at the top which usually has 4 pins, one for each of the 3 phases and another for ground. You may want to verify that your spindle is grounded correctly before you hook the spindle up.

Water cooled spindles will also feature two connections at the top. These are the inlets for water entry and exit. Cool water will enter the spindle through one then loop around the motor’s magnets which will heat the water up. Eventually the water will exit out of the spindle through the 2nd inlet and be cooled off through a radiator or go into a large reservoir to cool off before being recycled through the spindle.

 

Variable Frequency Drives (VFD)

VFD’s are what drive the spindle. They control the speed of the spindle by varying the frequency of the AC (Alternating Current) going to the spindle.

The basic interface of a VFD will consist of:

  • Power and status LED’s (Light Emitting Diodes)
  • LCD (Liquid Crystal Display) of the spindles current speed shown in RPM (Rotations Per Minute)
  • Potentiometer or buttons to increment or decrement the speed
  • Run and Stop buttons to run and stop the operation of the spindle
  • Some type of function key to change parameters or functions

The most basic controls for operation of the spindle are also available to be controlled externally via a breakout board of some type. This means you can have your CNC controller software automatically start / stop / change speed of the spindle as commanded by you or the programmed job that is being executed.

 

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