Flesher: Technical Support

System 3 Service Bulletin 004:

Pre-load Adjustment for System 3 Spindle Bearings

System 3 printwheel spindle assemblies use close-tolerance bearings which, when assembled in pairs in the System, have a pre-load that may vary depending on the grinding tolerance of the individual bearings. For the System 3, minimizing this pre-load without introducing free play between the bearings will reduce spindle friction and give more consistent positioning of the wheel. This will result in better appearance of vertical title base lines.

Normally, the pre-load can be reduced by adding shims between the outer races of the bearings in .002 inch increments until free play is felt; then removing the last .002 inch shim to remove the free play. Total thickness of the shims may range from zero to .008 inches.

Sometimes (but rarely), the pre-load must be removed by adding shims between the inner races of the bearings. If adding a shim between the outside races causes increased pre-load (and therefore increased friction), try adding a shim between the inner races instead. Use the same procedure as you would for adding shims between the outer races.

  1. To remove the spindle assembly from the System 3 machine, use the following procedure.
  2. Turn off the machine.
  3. Carefully push the cloth clamps to the rear of the *machine.
  4. Use a tie-wrap or a piece of wire to tie the foil selection mechanism to the top of it's travel to keep it out of the way.
  5. Remove the printwheel.
  6. Disconnect the two wires from the printwheel heater at the terminal board.
  7. Remove the printwheel heater box.
  8. Disconnect the flat ribbon cable from the terminal board at the top of the printwheel assembly.
  9. Place a sheet of cardboard under the spindle assembly to protect the table.
  10. Disconnect the tilt connecting link at the top of the spindle assembly and allow the spindle assembly to lay forward onto the cardboard.
  11. Remove the shaft clamp and thrust washer from the left tilt pivot shaft.
  12. Remove the four screws that hold each pivot shaft to the machine frame.
  13. Pull each pivot shaft out of the spindle assembly. Don't lose the second thrust washer from the inside left pivot shaft.
  14. Remove the spindle assembly to your work bench.
  15. Remove the motor mounting plate and the terminal board mounting chassis.
  16. Remove the bottom and middle spindle plate stiffener bars.
  17. Remove the six allen cap screws that hold the belt drive sheave and home sensor cup to the spindle assembly. Before removing the home sensor cup, note its relative position to the printwheel keying pin on the front of the spindle assembly so it can be reassembled correctly later. Carefully set aside all of the hardware.
  18. Remove the spindle oil line.
  19. Remove the six phillips head screws that hold the spindle housing to the spindle plate.
  20. Remove the six allen cap screws that hold the printwheel mount to the front of the spindle and remove the printwheel mount.
  21. Push the spindle out the back of the spindle housing
  22. Remove the remaining two phillips head screws that hold the bearing retaining ring to the spindle.
  23. Carefully push the bearings out the back of the housing.

REASSEMBLY

  1. Reassembly is the reverse of the above procedure except several precautions should be taken.
  2. 1. The spindle and spindle housing are precision machined parts designed so the bearings will fit into them without having to use excessive force. If the bearings are kept absolutely parallel to the spindle and spindle housing, they can be assembled without being forced. Any force used beyond hand force is too much and may cause damage.
  3. 2. Handle and reassemble the spindle bearings, in a clean environment. Any contamination can cause erratic bearing operation. If necessary, clean the bearings using clean lacquer thinner or other solvent. Re-lubricate the bearings with a suitable high temperature synthetic oil or compressor oil.
  4. 3. Each bearing has been modified with a groove on one side of the outer race. The bearings must be assembled with the grooves facing each other and at the bottom of the spindle housing. (The bottom is opposite the oil hole.)
  5. 4. If shims are added to reduce pre-load on the bearings, one .002 inch shim should be added at a time, the spindle reassembled and tested. If the pre-load is still too great, the spindle should be disassembled, another shim added and then reassembled and tested. Testing consists of determining that there is no free play in the bearings after reassembling the bearings, shims, printwheel mount, and bearing retaining ring. If free play is detected, remove one shim and reassemble.