Service Home How To Procedures ST-10/15/20 - Sub-Spindle Pulleys and Motor - Replacement - AD0979
Last updated: 06/22/2026

ST-10/15/20 - Sub-Spindle Pulleys and Motor - Replacement

AD0979

Revision A - 06/2026

Introduction

This procedure describes how to remove and install the sub-spindle pulleys and motor for the ST-10/15/20 lathes fitted with the A2-5 Finishing Sub-Spindle

The procedure applies to the following kits:

  • 93-5617 Pulleys and Motor Replacement

Note: Service kit comes with 3 items. The pulley on the servo is sweat fit onto the shaft. 

Important: Be sure to keep all hardware organized during the removal steps as they will be reused during reinstall. 

 

Remove Pulleys and Motor

1

Zero return B-Axis to home 

Power off and lock out the machine

Remove sheetmetal [1] and [2] to expose sub-spindle

2

 
Remove back panel [1]
 
Note: A cooling fan is attached to the rear panel. Before fully removing the panel, disconnect the fan’s electrical connector to avoid damage
 
Remove head cover [2] 
 
Remove service panel [3]
 

3

Break bolts [1] of the motor mount so that bolts are snug fit
 
Turn Cam Linear Guide [2] counterclockwise to loosen the tension on the belt
 
Remove bolts [3] to remove Sub-Spindle motor [4]
 
 

4

Note: Use service panel to gain access to bolts that mount the union to they spindle pulley
 
Remove bolts [1] to remove the union and draw bar [2]
 
Important: The union is heavy and if dropped it could lead to permanent damage. Have a surface near by with padding to lay the union and drawbar

5

Remove the belt [4] 

To remove the spindle pulley [3] you must remove bolts [1] that bolt onto the spindle cartridge 

Make sure to put aside the union spacer [2] 

 

Install Kit

1

Install new spindle pulley [3] with union adapter [2] using bolts [1] onto the spindle cartridge

Lay belt [1] onto spindle pulley [3] teeth

2

Once the spindle pulley is mounted indicate the radial runout on face [1] to NTE 0.001" TIR

Then indicate the axial runout on face [2] to NTE 0.0005" TIR

Once adjusted torque bolts to 13 ft-lbs

3

Re-install union and drawbar [2] using bolts [1]

Note: Use service panel to gain access to bolt holes onto the union [2]

Once installed indicate the radial runout on face [3] to NTE .0005"

After alignment torque bolts [1] to 13 ft-lbs

4

Install new motor [2] using bolts [1] onto the motor mount

Ensure bolts [1] are torqued to 25 ft-lbs

Important: Make sure to engage pulley teeth with belt before tightening bolts

To tension the belt you turn the cam linear guide [3] in the clockwise direction 

Tighten belt to 80 lbs and measure tension using a Gates Sonic Meter with parameters set to:

  • Mass: 3.5 g/m
  • Width: 15mm
  • Span: 160mm

Note: Check belt tension at different locations along the length of the belt. Manually turn the spindle to rotate the pulley

Once belt has been tightened tighten bolts [5] to 45 ft-lbs to secure motor mount

Re-check belt tension after torquing bolts. If out of specification, loosen bolts and repeat the procedure until within spec.

5

Re-install service panel [3]

Re-install head cover [2] 

Re-install back panel [1]

Note: All bolts are to be toqrued to 13 ft-lbs

6

Re-Install sheet metal [1] and [2]

Verification

After all cables have been reconnected power up machine 

In MDI input M143 P6000 which will rotate spindle the spindle forward at max RPM 

Press [RESET]  to stop the spindle

Then in MDI input M144 P6000 which will rotate spindle the spindle in reverse at max RPM