G3 CNC Spindle Won't Start: Slowly Turning

NOTE: Click on brown textThe Oregon Coast to show picture; click anywhere else to hide picture (Apple IOS: refresh page).

This page addresses a condition where you can jog, but the spindle turns very slowly with either M03 or M04.

This behavior can result from no speed command voltage to the variable frequency drive. Likely causes are bad Spindle Override pot, bad connection at TS2 on connect card, bad connection in MISC cable or 10-pin ribbon cable from MC2.

These instructions apply only to inverter drive on legacy spindle panel with TB1 terminal strip.

The instructions on this page assume you have performed initial tests here, and found that the spindle turns very slowly with either M03 or M04, and stops with M05.

Open the Spindle Drive Cabinet

Set the CNC control off, and turn the spindle drive cabinet switch to OFF.
Open the cabinet door, then use a small wrench or pliers to turn the 1/4" shaft to set the spindle drive power on.
Set the CNC power on and turn on servos.

Measure Voltage on TB1

TB1 is the long terminal strip that runs down the left side of the electrical panel. Terminal 1 is the top terminal on the strip. (For reference, here is PDF of spindle cabinet components)

In MDI mode, issue M05 S1750. This is to verify that neither M03 or M04 are engaged, and to set the spindle speed command voltage to about mid-point.
Measure the voltage from TB1-1 to TB1-2. This is the speed command from the Spindle Override Pot.

If the voltage from TB1-1 to TB1-2 is near zero volts DC after issuing S1750 from MDI, you will need to troubleshoot TS2 on the connect card in the CNC control.
If the voltage from TB1-1 to TB1-2 is about 5 volts DC, the display on the variable frequency drive should read about 60Hz.

OmniTurn G3 CNC: Spindle Turns Slowly With M03 or M04Legacy Inverter Spindle Drive (TB1)

Open the Spindle Drive Cabinet

Measure Voltage on TB1

OmniTurn G3 CNC: Spindle Turns Slowly With M03 or M04
Legacy Inverter Spindle Drive (TB1)