VFDSPINDLE VFD & CNC spindle wiring, sizing and setup

How to choose a spindle and VFD

One sequence, in the order that prevents the expensive mistakes. Most wrong purchases come from doing step four first.

1. Decide the speed range you cut in

Not the spindle's maximum — the band you actually work in. Cutting aluminium with small cutters wants high speed and modest torque; steel wants lower speed and more torque; wood and plastics mostly want speed and chip clearance.

Write down the range. Everything else follows from it.

2. Convert that into torque, then into power

Pick the torque you need at the speed you cut at, and use P = T × n / 9550 to get the power. Doing it in this direction — rather than buying a power figure and hoping — is what stops people discovering that a “bigger” spindle made no difference.

Use the speed/torque calculator and read the torque at your rpm, not at the spindle's maximum.

3. Fix the voltage before anything else

This is the step people skip and the one that cannot be fixed later with money alone:

Order the drive and the spindle as a matched pair. Choosing them separately is how the mismatch above happens. If you already own one, read its nameplate before buying the other.

4. Size the drive on current

Read the rated current off the nameplate and apply your margin. The sizing calculator also returns the supply current and a cable size, which is what your electrician will ask for.

Then check the three things a nameplate does not tell you:

5. Choose cooling for the duty, not the spec sheet

Long, loaded, continuous work → water, with a flow switch. Short and intermittent → air is simpler and good enough. See the cooling page and spindle types.

6. Decide whether you need braking

If a fast controlled stop matters — tool changing, an interlocked guard, cycle time — budget for a braking resistor and confirm the drive has the braking terminal and transistor to drive it. Not every drive does.

7. Budget for the parts people forget

8. Then compare prices

By this point you are comparing like with like. Doing it earlier means comparing a 220 V spindle against a 380 V one and wondering why one is cheaper.

The two-minute version: speed range → torque at that speed → supply voltage you actually have → drive current → cooling for the duty. Everything else is detail.

Once it arrives

  1. Identify the conductors before connecting anything.
  2. Wire it as shown, earth included.
  3. Enter the five motor parameters from the nameplate.
  4. First run at low frequency, no tool, direction confirmed.
  5. Then step up.

Parts

Spindles

Drives

Questions

What size VFD do I need for a 2.2 kW spindle?

Size on current, not power. Read the nameplate amps and pick a drive whose continuous output current exceeds it, with more margin if you are feeding it from a single-phase supply.

Is a bigger spindle always better?

No. Above the base frequency a spindle runs in constant power, so a higher top speed means less torque at that speed. Use the speed and torque calculator at the rpm you actually cut at.

Do I need a water-cooled spindle?

It depends on duty, not on the spec sheet. Air-cooled is fine for intermittent hobby work; continuous production usually justifies water, and a loop you can commission properly matters more than the spindle choice.

Sources and method

Three kinds of statement appear on this page, and each is labelled where it occurs:

Standards and documents

Further reading