Tube and Pipe and Roll Forming Mill Rebuild Procedures

Written by:  Robert A. Sladky, VP of Tube Mill Engineering

❒--All components that make up an “M” style gearbox must be inspected, compared to the measurements on the 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 scrapped and new components ordered in their place.

❒--Make sure you have detailed drawings from Yoder, that matches your model (old or new style) “M” style stands.

❒--Wash all components before inspection.  Clean parts are necessary before inspection, and before rebuilding.  Especially check all the hidden nooks and crannies of the inboard housing where accumulation of filings and trash can nest.

❒--Inspect a bare clean inboard housing by placing it on a granite plate.  Using a machinist square, check for squareness from the base of granite plate to front face of the housing.  You should not be able to put a .005” feeler gauge between the very top or bottom of the tower, and the squares blade.  If tower is not true, a determination will have to be made whether or not the housing can be reworked, or should be scrapped if it does not pass this checkpoint.

❒--Ensure the bores where the outside races install in the location of the worm shaft and bottom output shaft are within spec per the prints.  Ensure these bores are not oversized for whatever reason.  Take an outside race and do a test fit to these bores.  If the race will pass through this bore without any resistance, or you can get a .002” feeler gauge between the race and the bore, the housing will need to be sleeved, or replaced. Follow this inspection for the races of the bottom and top shafts as well. 

Many times, the bottom of the bore where the bearing race sits will be indented in one direction from the years of service and pressure on the shafts bearings.  This out of round condition must be corrected, for failing to correct this can affect alignment, bearing preload, and can cause an outside race to crack under load.  Also, look for damage due to the spinning of the race from a bearing failure.  Check for cracks in the housings, especially the top of the bore where the bottom bearing is located on the face of the inboard housings, for that area is very thin.  

❒--Inspect the width of the tower legs, where the top-bearing block will be installed.  If more than .003” undersize from the print dimension, you will need to decide if you can economically machine and install new Gibbs to bring the width measurement back into specification, or to scrap the housing.

❒--Inspect the width between the tower legs of the inboard stand.  If wider than .003” of the measurement on the print, you will again need to decide if this can be reworked, or replaced.

❒--Inspect the top-bearing block.  The width should be the same as the tower leg width or no more than .001” narrower for a proper snug fit when assembled.  Check the bore where the outside race resides.  Follow the same inspection procedures as previously outlined.

❒--Inspect the bearing end caps.  Replace the end caps if excessive wear is present. 

❒--Inspect top and bottom driven shafts.  The O.D. of the shaft, where the roll space is should not be more than .001” per 1.000” O.D. undersize. (Example, 2.000” shaft, max undersize tolerance, .002”, or 1.998”? O.D.) Bearing journal O.D.should not be more than .001” undersize for proper fit.  Put the shaft between centers on a lathe, and check for run out.  Anything more than .001” the shaft needs to be reworked (hard surface chromed) or replaced. See this link for checking O.D. and run out of driven shafts.

❒--Inspect worm gear and worm shaft. Determine if they need replacement at this time.  Always try to replace these in match sets.  In the area where the seal rides on each end of the worm shaft, install a “ready sleeve” to repair the area that might have been grooved by the seals previously.  It is good practice to install this “ready sleeve” even on new worm shafts, for the ready sleeve is made of highly polished hardened stainless steel, and offers much longer seal life.

❒--Inspect all transfer gears from bottom shaft, through connecting links, to the top shaft. Insure the teeth and the bore where the shaft mounts (top and bottom) and where the bearings ride (idler gears) are within spec.  Do not forget to check for face wear.  Compare old units to new gears or verify to the prints to qualify these gears before use.  Insure the correct number of teeth are used, and if they are going to be used for new or old style, (they are not the same) and for equal or un-equal gear ratio gearboxes.

❒--Inspect the link plates for bore wear, face wear, and O.D. of the pins.  Replace any components that do not pass inspection.

❒--Measure all the sleeves/spacers that will be part of the assembly of the top, bottom shaft assemblies, and compare them to the prints. These need to be within .001” of length for proper stack up of components during assembly.  These components locate the reference points of gear mesh, alignment etc.

❒--Inspect the lead screws of the inboard and outboard top heads.  Use new brass washers, and insure the dial is readable, and the top heads have the pointers installed.  Inspect the top caps for cracks, especially where the lead screw nut is bored through.

❒--Inspect the outboard stands bearing bores, etc., using the same procedures outlined above for the inboard stands.  Yoder makes more than one design of outboard stands.  Some have removable bolt on top heads, others are close-capped casted tops.

❒--Take the stainless steel accordion that is installed between the top bearing block and bottom shaft of the inboard housing, and stretch it out so the pleats are even and apart from each other.  Taking some of the “plastic dip” used for dipping/coating the handles of tools, etc., dip the sides of the accordion where it will fit to the sides of the towers, so as to develop a little bit better seal to keep coolant and trash out of the gearbox.  This helps, but is not a waterproof fix.  Operators must be trained to continually watch to insure the coolant is not spraying directly, or even in-directly splashing against this area, allowing coolant to get into the oil sump.  Coolant will quickly destroy all the efforts of the best rebuild.

Bottom Input Worm Shaft Assembly

❒--Assemble the worm shaft with bearings and new shims per Yoder’s print.  Put a light coat of grease on the outside races before installing bearings on the shafts and 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 gear. 

❒--Once assembled, use a dead blow hammer to each end of the shaft insures the shaft and bearings are seated. Next check the preload of the bottom worm shaft using a dial type inch pound torque wrench.  Add or subtract the shims on the end caps to obtain the following preloads:

• M-1 ½ & M-2’s, 5-10 inch pounds of rotational drag.
• M-2 ½’s, 10-15 inch pounds of rotational drag.

See the two links below for proper procedure for preloading bearings:

• Properly Preloading Tapered Roller Bearings for Tube and Pipe Machines
• Setting Preload For Taper Roller Bearings - Tech Tip for Tube, Pipe or Roll Forming Mill

❒--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.

Bottom Output Shaft Assembly

❒--Assemble the bottom output shaft with bearings, sleeves/spacers, brass worm gear, new shims and related parts as outlined in Yoder’s prints.  Coat the outside bearing races with a light coat of grease before assembly of bearings and end caps.

❒--If the outboard bearing block retainer has been modified to incorporate a seal, leave the seal out until final assembly.

❒--Next check the preload of the bottom worm shaft using a dial type inch pound torque wrench as previously outlined.   Add or subtract the shims on the end caps to obtain the following preloads:

• M-1 ½ & M-2’s, 15-20 inch pounds of rotational drag.
• M-2 ½’s, 20-25 inch pounds of rotational drag. 

❒--Put the inboard housing on the granite plate, and insure it is sitting flat on the plate.  Clamp down if necessary.  Taking a height gauge, check the height on the end of the driven shaft, then towards the gearbox.  Should be within .002” of each other.  If not, the bore in the housing for the bearings might not be in order.  Repair or replacement of the housing might be in order if this problem exists. 

❒--Next, apply Dye-Kem Blue, or heavy grease to a couple areas of the teeth of the brass worm gear.

❒--Re-install the worm shaft.  Rotate the worm shaft, and observe the tracking points the worm shaft makes in the brass worm gear.  Insure the track is in the center of the brass gear.  Adjust the shims to either side of the brass worm gear, to obtain, and maintain a centered tracking pattern.

❒--Rotation should be smooth and even as the worm shaft and bottom shaft with the brass worm gear are rotated a full 360 degrees. If assembly binds up at any point, or the worm shaft turns harder in some places during the 360 rotation, then you might be experiencing a brass gear that is not concentric, or the gears may not have been cut correctly. 

❒--Next check shoulder alignment of the bottom shaft.  Using a shoulder alignment tool (SAT) or depth mic measuring off a sizing roll, insure the shoulder measurement to be as outlined on the Yoder print.

❒--Shims must be moved from inboard to outboard or vise versa to obtain the proper shoulder alignment measurement.  Whatever value of shims you swap to move the bottom shaft to obtain the shoulder measurement, the same amount must be moved from one side to the other side on the brass worm gear to keep it centered on the worm shaft.   So many times this is totally forgotten.   Example.  If you take a .005” shim from the rear bearing end cap to the front side, you will have to move .005” worth of shims from one side to the other side of the brass gear to maintain center to the worm shaft.  

Top Output Shaft Assembly

❒--Assemble the top shaft per Yoder print.  Do not assemble the transfer link plates at this time.  

❒--Your assembly will be accomplishing three things at once.  Bearing preload, snug fit of the bearing block to the tower legs with the end caps, and shaft shoulder alignment.  First, we must secure/set the first two, bearing preload and snug fit to the tower legs.  Again, apply a light film of grease to the bearing races before assembly.  If the outside bearing block end cap has been modified for a seal, leave it out for now.  Next check the preload of the top shaft using a dial type inch pound torque wrench as previously outlined.  Add or subtract the shims on the end caps to obtain the following preloads: 

• M-1 ½ & M-2’s, 15-20 inch pounds of rotational drag.
• M-2 ½’s, 20-25 inch pounds of rotational drag. 

❒--Next check shoulder alignment of the top shaft same as you did for the bottom shaft.  Using a shoulder alignment tool (SAT) or depth mic to insure the shoulder measurement as outlined on the Yoder print. 

Outboard Stand Assembly

❒--Assemble top and bottom bearing block assemblies of the outboard stands per Yoder print, applying a light film of grease to the cage bearings.

❒--Align the driven shafts of the inboard stand to the same centers as the bearing blocks of the outboard stand so you can engage the outboard stand to slide over the O.D. of the driven shafts.  Note the slip fit as you slide the outboard stand onto the driven shafts.  Does the stand want to pick itself up during the slide on?  If so, this might be a result of a worn bottom footprint of the outboard stand.  Repairs or replacements might need to be in order if this condition is found.

❒--Parallel the driven shafts by adjusting the top lead screw of the inboard and outboard stands between a pair of spacers or parallel blocks, taking up the entire backlash and then setting the dials to the same number.

❒--Next verify the shoulder alignment from top to bottom shafts are held to .001” of each other, otherwise marking from the tooling will result when put in service.   Verify with a straight edge. 

Final Assembly of Inboard Gear Box and Outboard Stand

❒--Assemble the transfer gears per Yoder’s print to the required ratio for the gearbox.  Example, sizing and fin passes are equal ratio gearboxes.  Breakdown passes have an unequal gearbox ratio.  Install new brass washers, etc. on bottom pin between outer link plate and cotter key for final assembly.

❒--Position a .020” feeler gage blade to set the clearance between the oil diverter tray and the brass worm gear and tighten the bolts that retain the tray. 

❒--Install seals on all bearing end caps.  (Use double lip seals for longer life)

❒--Fill gearbox with oil to level on the sight glass and grease all bearings until you see grease coming out the seals, or endcaps, or inside of end caps in the housing. Do this gradually so as not to blow out the seals

❒--Secure the assembled inboard and outboard stand to the test stand plate.  Hook up the pulleys and motor, and run in the gearbox for at least two hours.

❒--As soon as you start the test, start greasing of the bearings as it is running until grease comes out the seals.  Again, do this gradually so as not to blow out the seals.  This is one of the best times to grease the taper roller bearing, when they are rotating, for this evenly distributes the grease throughout the bearing assembly.

❒--During testing, monitor the bearings for heat, or vibration.  Check the oil transfer from the oil tray to the transfer gears.

❒--Once test is done, remove the outboard stand and check top and bottom shaft for looseness.  Shafts should have remained tight.

❒--Install fiberglass cover (new style) or cast iron cover (old style). Remove pulley from gearbox.  Drain the break-in oil in the gearbox and fill it with new oil. (Do not reuse the old oil for further break-in/testing as it will contain fines that can be detrimental to the next gearbox)   Rebuilt gearbox is now ready for installation.  Tag unit as equal or unequal gearbox.    Old style and new style gearboxes can be used on the same mill.  The mounting holes, and centers from bottom shaft to mill base are the same.

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