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Tube and Pipe Gear Box Rebuilding Procedures

Tube and Pipe Gear Box Rebuilding Procedures


  • All components that make up any make of gearbox must be inspected, compared to the measurements on the manufacturers prints to qualify the components for rebuild.  Those that do not pass inspection have to be determined if they can reworked efficiently to make them usable, or scraped and new components ordered in their place.
  • Make sure you have detailed drawings from the manufacturer of the gearbox that matches your model you are rebuilding.
  • Wash all components before inspection.  Clean parts are a must before inspection, and before rebuilding.  Especially check all the hidden nooks and crannies of the housing where accumulation of filings and trash can nest.
  • Insure the bores where the outside races install in the location of the worm shaft and top and bottom output shafts are within spec per the prints.  Insure these bores are not oversized for whatever reason.  Take a new outside race and do a test fit to these bores of end caps or housings.  If the race will pass through this bore without any resistance, the housing or end cap will need to be sleeved, or replaced.   Also look for damage (shaft journals) due to the spinning of the inside races from a bearing failure.
  • Inspect worm gears and worm shaft. Determine if they need replacement at this time.  Always try to replace these in match sets.  Most rebuild kits have a “ready sleeve” to install in the area where the seal rides. If the make or model of gearbox does not offer this “ready sleeve” with the kit or seal, consider installing this component regardless. Your bearing supplier can fit any application for any size shaft.

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Input Worm Shaft Assembly

  • Assemble the worm shaft with bearings and new shims (“starting nominal thicknesses”) per manufacturers print.  Insure the bearings are seated to the flange they are designed to fit up against, especially when using a bearing heater to install.  A bearing that is not tight against its shoulder will put the worm shaft out of alignment and you will loose the bearing preload after run in once the bearings seat.  Put a light coat of grease or oil on the outside races before installing end caps.

  • Do not install the seals yet, this will be done after the shaft and bearings are preloaded, and tracked with the brass worm gears.  Installing the seals at this point will give us a higher preload value, and not tell us the true rotational resistance we are trying to measure on each shaft.
  • Add or subtract the shims on the end caps to obtain the manufacturers recommended inch pound value of rotational drag.  Keep the amount of shims equal on both end caps to keep the worm shaft centered in the housing. Use a dead blow hammer to insure the shaft and bearings are seated. 

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Note:  Insure the torque of your fasteners is the same as your final assembly.  If you lightly tighten the fasteners during preload setting, and then tighten down harder on the final assembly, you will affect the final preload of the bearings due to the compression of the shims, especially if they are made of plastic or aluminum.  Use a torque wrench if needed to insure all fasteners are assembled to the same torque at all times during all preload and final assembly procedures.

  • Once the preload is set, remove one end cap, and remove the worm shaft assembly so the bottom output shaft can be assembled and checked for preload.

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Bottom Output Shaft Assembly

  • Assemble the bottom output shaft with bearings, sleeves, brass worm gear, new shims (“starting nominal thicknesses”) and related parts as outlined in the manufacturer’s prints.  Coat the outside bearing races with a light coat of grease or oil before assembly.
  • Do not install the seals yet, this will be done after the shaft and bearings are preloaded, and tracked with the brass worm gears.  Installing the seals at this point will give us a higher preload value, and not tell us the true rotational resistance we are trying to measure on each shaft.
  • Add or subtract the shims on the end caps to obtain the manufacturers recommended inch pound value of rotational drag.  Keep the amount of shims equal on both end caps to keep the output shaft centered in the housing. Use a dead blow hammer to insure the shaft and bearings are seated. 

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Note:  Insure the torque of your fasteners is the same as your final assembly.  If you lightly tighten the fasteners during preload setting, and then tighten down harder on the final assembly, you will affect the final preload of the bearings due to the compression of the shims, especially if they are made of plastic or aluminum.  Use a torque wrench if needed to insure all fasteners are assembled to the same torque at all times during all preload and final assembly procedures.

  • Next, apply Dye-Kem Blue or grease to a couple areas of the teeth of the brass worm gear.
  • Re-install the worm shaft.  If your make and model has timing marks, line these up per manufacturer’s directions.   Rotate the worm shaft, and observe the tracking points on both the worm shaft and brass worm gear.  Insure the track is in the center of the brass gear and worm shaft. (Compare to the illustrations in your gearbox instruction sheet)  Adjust the shims to either side of the brass worm gear, or worm shaft to obtain, and maintain a centered tracking pattern on both.
  • Rotation should be smooth and even as the brass gear and worm shaft are rotated.  If the assembly binds up at any point, or the worm shaft turns harder in some places during the 360 degree rotation of the output shaft, then you might be experiencing a brass gear that is not concentric, or the gears may not have been cut correctly.

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Note: If your make and model of gearbox has a top output shaft that is driven by the worm shaft also, such as Cone Drive models, do the same procedure for the top output shaft as you did for the bottom output shaft.  Otherwise if the top shaft receives it power from a simple set of straight transfer gears, only the preload of the bearings on this top output shaft will be needed.  No tracking of straight transfer gears is usually necessary.

Final Assembly of Gear Box

  • Assemble the transfer gears (where applicable) per manufacturers print, and to the required ratio for the gearbox.  Example, sizing and fin passes, equal ratio gearboxes.  Breakdown passes, unequal ratio gearbox.
  • Install seals on all bearing end caps.
  • Fill gearbox with oil to level on sight glass or check plug.
  • Secure the assembled gearbox to a test stand.  Hook up the pulleys and motor, and “run in” the gearbox for at least two hours. 

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Note:  Insure motor and input shaft is turning the same direction as it will when installed on the mill.


  • As soon as you start the test, start greasing the bearings (where applicable) as it is running.  Do this gradually so as not to blow out the seals.  Those gearbox designs where oil lubricates all the bearings, this step will not be required.
  • During testing, monitor the bearings for heat, or vibration.  Neither one should be excessive. 
  • Remove pulley from gearbox.  Drain the break-in oil in the gearbox and discard it, do not use this oil for any other “run in”.  Fill tested gearbox with new oil.  It is now ready for installation on the mill.  Tag unit as equal or unequal gearbox and for which mill it fits.

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Written by Robert Sladky, VP of Tube Mill Engineering

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