Service How To Procedures ST Lathe Spindle Replacement
Last updated: 04/03/2020

ST Lathe Spindle Replacement

This serves as a general guide for replacing spindle cartridges on ST style lathes.

Procedure Requirements

Removing the Old Spindle

1

  • Zero return the machine to allow for plenty of access to the spindle head
  • Power off and lock out the machine
  • Remove the coolant collector box, rear, and front panel to gain access to the spindle head

2

  • Remove the anti-rotation bracket that seats around hydraulic union drain hose
  • Lock the spindle to prevent it from rotating
  • Break the screws [1] loose that connect the adapter to the union
  • Disconnect the hydraulic lines [5] from the hydraulic union [2]. Note the clamp/unclamp hose and port orientation
    •  Note: Have plugs or baggies and rubber bands to cover the hoses to prevent hydraulic fluid from coming out and debris from getting in.  Keep the hoses pointed up and tucked away on the side of the spindle to prevent fluid from coming out
  • Remove the screws and slowly remove the union and drawtube assembly
    • Caution: The union is heavy and if dropped  it could receive permanent damage
    • Have a box or table nearby with padding to lay the union in and support the drawtube
  • Remove the adapter screws [3] that secure the adapter [4] to the spindle shaft.
  • Remove the adapter [4] (See ST Adapter Replacement Guide if the adapter must be replaced as well)
    • Early machines have a clearance fit adapter that will easily be removed once the screws are broken loose
    • Later machines (ST-15 through ST-30  11/2018 and after;  ST-10 02/2017 and after) will have a sweat fit adapter
      • To remove sweat fit adapters use a torch and evenly heat the outer diameter of the mating surface
      • After a few minutes begin gently dislodging the adapter until it slips free
      • Do not pry or cause damage when removing - you will need to re-use this part
      • Let it cool down slowly to prevent distortion

3

  • Break loose the motor mount plate screws [4]
  • Loosen the nut on the tensioner block [3] and loosen the belt tension on the belt by turning the socket head cap screw (SHCS) counter-clockwise
  • Remove the belt from the pulley
  • Break loose the drive sprocket [1] screws
  • Remove the drive sprocket
    • Some machines have a sweat fit drive sprocket that will clear the housing bore when the spindle cartridge is removed.  These won't need to be removed.

4

  • Removing the encoder ring [2]:
    • The encoder ring [2] could be a loose fit to the bearing lock on the rear of the spindle as shown, an encoder mount that mounts to the bearing lock, or a sweat fit to the bearing lock or encoder mount
    • On ST-30 gearbox and ST-35/gearbox machines the ring mount may be for the home switch instead. (machines 03/2019 and after). On these machines the non-contact encoder will be on the output of the motor shaft. In this case leave the encoder on the motor but remove the ring on the spindle for the proximity switch.
  • If loose fit: loosen screws [1] and carefully remove the ring without causing damage to the outer ring shield
  • If sweat fit: remove the screws [1] from the through holes, install the screws to the threaded hole pattern and use them as jacking screws to evenly remove the encoder ring
    • Use a stone to smooth out the marks left from the jacking screws when you're done
  • Temporarily remove the read-head [3] (or proximity switch), read-head plate [4], and bracket [5]
  • Secure the read-head out of the way to the motor mount brace with a cable tie
  • If there is an encoder ring mount: Heat the mount lightly with a torch, mount not to exceed  (230 °F, 110 °C ), and gently tap off the same way the sweat fit adapters are removed

5

  • Break loose the nut [1] on the spindle oil injector nozzle [2]
  • Remove the nozzle [2]
  • Break loose the spindle retainer cap [3] screws
  • Remove the retainer [3]
  • Remove the spindle cartridge [4]
    • Tap the rear of the cartridge with a plastic mallet to break it loose from the spindle bore
    • Place a strap around the spindle cartridge and use a hoist to help support the load as you remove it
  • Pack the spindle in the packaging the new spindle came in to return it if it is under warranty
  • Some spindles have a wave spring [5] or o-ring in the rear of the spindle housing bore
  • Remove this and clean it if necessary
  • Clean the spindle housing bore with scotch brite and alcohol
  • Wipe out all debris
  • Wipe with a light coat of SHC 625 or Mobil 5W20 oil or equivalent
  • Coat the o-ring or wave-spring with a light coat of Red-I grease or equivalent
  • Re-install to the rear of the spindle bore
    • Wave-spring goes pointed side down into the shoulder

Install New Spindle

1

  • Install the new spindle cartridge using a strap and hoist
    • A 2"x2" piece of wood (or other soft material) placed through the bore of the spindle can be useful in order to get the rear of the cartridge to seat square in the bore of the spindle head
  • You must align the hole in the bearing spacer [3] with the injector nozzle [2] hole in the casting
  • Install the injector nozzle [2]
    • Thread it all the way in, then back it out one to one and a half turns
    • If it can't thread all the way in then the hole in the bearing spacer is not aligned correctly.  You will need to pull the cartridge out and re-align.
  • Adjust the injector nozzle so the flat side is facing forward (towards the chuck side of the spindle)
  • Hold in place and tighten the nut [1]

2

  • Install the spindle retainer cap [2]
  • Snug the spindle cap srews [3]
  • Use a .001" shim [4] between the cartridge and the spindle retainer [2]
  • Tap the spindle retainer with a plastic mallet until the shim clears every section of the cartridge
  • Torque the retainer screws [3] in a star pattern.
    • Note:You may need to start at a 1/3 of the torque value and torque them down 3 times. Torqueing down all the way the first time may displace the retainer cap and require it to be reset.
  • Sweep between the cartridge and the retainer cap one last time to verify the .001" shim has clearance all the way around [4]

3

  • Install the non-contact encoder ring [2]/[6] or proximity switch ring:
  • If the ring is slip fit, install and indicate in to .001" TIR
  • If the ring is sweat fit it may mount directly to the spindle bearing lock as with the ST-20 OR it may mount to an encoder ring mount [7] that then mounts to the pulley [8] as with the ST-10
  • For the ST-10 mount, install the ring [6] to the mount [7] first:
    • Heat the encoder ring on a hot plate to a max temperature of 248 °F (120 °C) 
    • Install to the ring mount, press evenly to seat it square into the shoulder
    • Heat the ring mount and encoder ring assembly to a max temperature of  248 °F (120 °C) for 20 minutes
    • Install the assembly to the pulley shoulder, press evenly to seat it square into the shoulder
  • Once the ring has cooled down check the outer diameter runout NTE 0.001" TIR
  • Install the read-head bracket [5], read-head plate [4], and read-head [3]
  • Set the gap using the read-head/ring shim

4

  • Installation of the pulley is reverse of removal (ST-15/20/30/40). The ST-10 model from 08/2016 and onward, have sweat fit pulleys that do not need to be removed.
  • Slip the pulley onto the spindle shaft and snug the screws [1] into the spindle bearing lock [2]
  • Indicate the pulley, NTE .001" TIR
  • Torque the pulley screws [1]
  • Install the belt to the spindle and motor pulleys
  • Tension the belt by tightening the socket head cap screws [3] (SHCS) in the clockwise direction
    • Tighten both screws evenly until belt tension is achieved
    • Check belt tension with the Gates Sonic Meter, reference the Belt Tension Specs
    • Tighten the nut on each screw once belt tension is set
    • Verify the belt tension is correct
  • Torque the motor mount screws [4]
  • Check the gap between the encoder and read-head to make sure the shim still drags lightly between both surfaces

5

  • A hot plate will work best to uniformly heat the adapter
    •  Caution: Do not exceed 248 °F (120 °C) when heating the adapter
  • Place the adapter smaller diameter face down on the hot plate
    •  Caution: Be sure to use high temperature heat resistant gloves when sweat fitting the adapter
  • When you install the adapter you must move quickly as the aluminum will cool fast
  • With the adapter at about 248 °F (120 °C) on the hot plate - take one screw [1] and put it into the adapter washer [2] to have it ready
  • With gloves on, using both hands, take the adapter and quickly slip it onto the shaft
  • Press evenly on both sides, until you feel it seat  
  • Rotate it until the hole patterns line up
  • Take the screw and adapter washer and quickly run down the one screw into a hole
  • Quickly run the rest of the screws down in a star pattern
  • Torque the screws in a star pattern to ensure the adapter seats
  • Then break the screws loose but leave them snug while the adapter cools
  • Torque screws again once the adapter has cooled
  • Once cooled measure the inner radial runout [3], not to exceed 0.001"
  • Measure the axial runout [4], not to exceed 0.0005"
    • Production Tip: If you find that you're having a hard time getting the adapter to seat and have accepatable runout, then try the following.  After you slip the hot adapter on the shaft, snug all the screws down, and then lightly indicate the adapter on the inner radius [3] while using a plastic mallet on the outer diameter. When the runout is within spec, slowly torque all of the screws down in a star pattern being careful not to induce runout.

6

  • Install hydraulic union:
  • A limited number of ST-10's have a sweat fit from the adapter to the union.  If you have this condition you can heat the adapter with a torch for about 3-5 minutes until the bore grows enough to allow the hydraulic union to slip in.
  • All other lathes - install the union and snug the screws
  • Indicate in the steel strip [1] NTE 0.0005" TIR
  • Check the deflection measurement [2] by placing the indicater on the non-rotating body of the union and then rotate the pulley.  The deflection should be less than 0.001".
  • Re-attach the clamp/un-clamp hoses and the drain hose
  • Warning: Do not over tighten or you could crack the alumnium assembly

Verify Spindle Lubrication - Bottle Test

After replacing the spindle you will want to make sure it gets adequate oil.

For testing, refer to the link below.

 

Spindle Lubrication Test

Note: If you have an old style oil pump that does not have sight glasses, then you must install the sight glass upgrade.

For installation, refer to the link below.

Drip Sight Glass Installation

Check Spindle Vibration

1

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