SPINDLE REPAIR GLOSSARY

The glossary section is here to increase your understanding of spindle related terminology. If you need additional information, please contact us, we love to talk about what we do.

Stator

The stator is the stationary part of the electric 3 phase induction motor system found in a spindle. It can also be known as a field. The stator consists of wire windings that when energized create a magnetic field that pushes the rotor making the spindle shaft rotate.

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Failures:
Short to ground- 1 or more of the phases are no longer insulated from ground (spindle)
Short leg to leg- 2 of the 3 phases are no longer insulated from each other
Broken wire- The wire of 1 or more phases has broken
Single phase- Not all 3 phases are functioning causing loss of power

Causes of failures:
Overload: Exceeding the stators recommended power rating causes heat which causes the windings insulation to break down.
Contamination: If conductive contamination (water based coolant) is allowed to contact the stator windings short circuits can occur.
Overheating: due to lack of cooling
Incorrect voltage to hertz ratios

Recommended repair procedure: When a stator fails our incoming QC inspection we recommend that it be rewound. The stator windings are removed and replaced with new windings with new insulation. The price for this service varies with stator size.

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ROLLER BEARINGS

Roller bearings are used in spindle applications that require a high level of radial load capacity. Some examples of this are large centerless grinding spindles, large low speed milling spindles and spindles that have radial loads from drive belts.

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Roller bearings are used in spindle applications that require a high level of radial load capacity. Some examples of this are large centerless grinding spindles, large low speed milling spindles and spindles that have radial loads from drive belts.

The drawback to roller bearings is low to no axial load capacity and low speed capacity.

Spindle roller bearings can be mounted using two different methods. Straight bore rollers slide onto the shaft and rely on the size of the shaft and housing to preload the bearing. Tapered roller bearings have a tapered race ID that matches a taper on the shaft. The farther up the taper the bearing is placed the more the inner race expands which increases the preload. Different materials are used in the raceways and rolling elements to increase the speed capability of the bearing. It is extremely important to replace spindle roller bearings with a style that meets or exceeds the applications requirements or premature failure can occur.

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CERAMIC DISC TYPE ROTARY UNIONS

Ceramic disc type rotary unions are used in machine tool spindle applications of various makes, models and applications. This is a typical set up where one end mounts to the drawbar and one end mounts to the machine.

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Ceramic disc type rotary unions are used in machine tool spindle applications of various makes, models and applications. This is a typical set up where one end mounts to the drawbar and one end mounts to the machine.

During use without through tool coolant the two discs are separated. When the coolant is turned on the pressure pushes the machine mounted disk forward until it contacts the disk on the drawbar.

If you look closely you can see the wear on the disk surfaces. This causes coolant to leak and potentially enter the spindle. This causes the bearings to be contaminated and eventually fail.

Check these surfaces every time you replace a spindle. Always replace the disks as a set. They wear together during use. Unmatched sets will fail prematurely. Follow the OEM installation and break in procedures.

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THERMISTOR

A thermistor is a type of resistor whose resistance varies with temperature. Spindle usage: Thermistors are placed on or near the spindle stator to monitor the heat of the motor windings. The machine control monitors the outputs of the thermistor and if the outputs reach an overheat level the spindle is shut down.

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Defenition: A thermistor is a type of resistor whose resistance varies with temperature.

Spindle usage: Thermistors are placed on or near the spindle stator to monitor the heat of the motor windings. The machine control monitors the outputs of the thermistor and if the outputs reach an overheat level the spindle is shut down.

There are two types of thermistors used in spindles, one increases the resistance as the temperature increases and one decreases resistance as the temperature increases. For obvious reasons the proper thermistor needs to be installed if they are found to be faulty or if the field needs to be rewound.

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Spindle Shaft

The Spindle Shaft consists of the Pulley Taper, Bearing Journal, Shaft Pilot, Threads, Shoulder, and Shaft Tooling Face. Definitions and explanations of each individual component are described here.

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Pulley Taper

Shaft Pulley Interface
This is the location that a pulley, gear or coupling sits on the shaft. It is important to make sure this surface is to specification (size and run out) or the following may result:
-Run out
-Vibration
-Fretting
-Noise
-Poor part finish
-Decreased bearing life
-Coupling damage
-Rotary Union Damage

Northland Tool & Electronics like to receive the customer’s pulley gear or coupling for the following reasons:
-Check for wear
-Check the fit to the shaft
-Check for fretting

Having these parts also makes it possible for Northland Tool to balance your spindle as a complete assembly with all the rotating components. This increases spindle life and decreases the chance of poor part finish and vibration.


Bearing Journal

This is the location on the rotating shaft that the ID of the bearing seats. It is extremely important to have the shaft bearing journal within micron tolerances for size, parallel to the shaft centerline and perpendicular to the bearing shoulder.

Depending on the bearing design the shaft bearing journal can be straight or tapered (commonly used with tapered roller bearings). The tapered journal must have all the characteristics of a straight journal but must also be checked for the proper angle. If this angle is not correct the roller bearing will not preload properly causing premature bearing failure, vibration, heat, poor part quality and noise.

Spindle manufacturers have realized that by changing the characteristics of the bearing shaft and housing fit tolerance they can manipulate the clearances in the bearings. This allows spindle manufacturers to manipulate spindle speeds and load capacities. As a spindle rebuilder we document the methods each spindle OEM is using on each model that they manufacture. This gives us a comprehensive guide for the tolerances our grinding room needs to meet. Many spindle repair companies either do not grasp this concept or use outside vendors for their grind plate grind work and these important tolerances are not achieved. This definitely causes shorter spindle life and poor spindle performance.


Shaft Pilot

The shaft pilot is a guide for the tool usually used in ID grinding spindles. It is important to check the pilot for size and run out. If it is out of specification it can result in the following:
-Tool run out
-Vibration
-Imbalance from run out
-Part chatter
-Poor surface finish
-Premature wheel wear
-Premature bearing failure

If a spindle pilot is out of specification it can be fixed with a grind plate grind. Spindle repair companies that do not have in house grinding capacity have been known to “cheat” by grinding the pilot in assembly to remove run out. This causes the pilot to be oversized and not hold the tooling properly.


Threads

Shaft Threads
Shaft threads are used with many different items. Here are some examples:
-Bearing capture nuts
-Tooling interface
-Pulley capture
-Drawbar capture
-Front and rear cover capture
-Preloading of the bearings

If the treads are out of specification the following can occur:
-Gauled parts
-Misaligned bearings
-Improper tool change
-Improper preload of the bearings
-Axial movement of the shaft
-Inability to assemble the spindle correctly
-Poor tool retention
-Inability to remove tooling

Threads can be repair using many different techniques. We can replace damaged or worn threads on spindles with external threads for tool holding. This is common for surface grinding, OD grinding and manual tool change spindles.


Shoulder

Housing Bearing Shoulder

The housing bearing shoulder contacts the bearing outer race and locates it parallel to the shaft centerline. It is critical that the housing bearing shoulder is perpendicular to the shaft centerline and has no run out.

If the housing bearing shoulder is not held to micron tolerances the following can occur:

-Misalignment between the inner and outer bearing race
-Point loading on the outer race
-Improper preload of the bearings
-Vibration during spindle use
-Poor part finish
-Poor spindle life

Every housing bearing shoulder is checked in our spindle evaluation. If our evaluation finds them to be out of tolerance they can be easily fixed in our grinding department. Many other spindle repair companies do not have in house spindle grinding departments so this step of the rebuilding process is often overlooked by them. This results in poor spindle performance and reduced spindle life.


Shaft Tooling Face

This is the area of the shaft that is perpendicular to the spindle centerline and contacts the tooling. Tooling faces can be found in ID grinding, HSK and BIG PLUS tooling interfaces. It is crucial to have the tooling face to specification as the following can occur:

-Tooling will “cock” causing run out
-On BIG PLUS and HSK the face MUST be at a certain position in relation to the taper or improper dual contact will occur
-Poor contact will cause fretting resulting in further spindle damage
-Poor surface finish
-Vibration

Tooling faces can not be ground plate ground as chrome plating does not adhere well enough to prevent chipping or flaking. Different repair options are available depending on the design of the spindle.

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Spindle Housing

The Spindle Housing is home to the Flange Housing Flange, Shoulder, and the Bore Housing Bearing Bore. Definitions and explanations of each individual component are described here.

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Flange Housing Flange

The housing flange is typically a ring attached to the OD of the spindle housing. It is used to locate the spindle in the machine tool and usually has holes bored into it for the mounting bolts. The mating surface of the flange needs to be perpendicular to the spindle centerline. The mounting surface must also be burr free to avoid misalignment during spindle installation.


Shoulder

Housing Bearing Shoulder
The housing bearing shoulder contacts the bearing outer race and locates it parallel to the shaft centerline. It is critical that the housing bearing shoulder is perpendicular to the shaft centerline and has no run out.

If the housing bearing shoulder is not held to micron tolerances the following can occur:

  • Misalignment between the inner and outer bearing race
  • Point loading on the outer race
  • Improper preload of the bearings
  • Vibration during spindle use
  • Poor part finish
  • Poor spindle life

Every housing bearing shoulder is checked in our spindle evaluation. If our evaluation finds them to be out of tolerance they can be easily fixed in our grinding department. Many other spindle repair companies do not have in house spindle grinding departments so this step of the rebuilding process is often overlooked by them. This results in poor spindle performance and reduced spindle life.

Bore Housing Bearing Bore

This is the location on the stationary housing that the bearing seats. It is extremely important to have the housing bearing bore within micron tolerances for size, parallel to the housing centerline, perpendicular to the bearing shoulder and concentric to the other housing bores in the assembly.

Spindle manufacturers have realized that by changing the characteristics of the bearing shaft and housing fit tolerance they can manipulate the clearances in the bearings. This allows spindle manufacturers to manipulate spindle speeds and load capacities. As a spindle rebuilder we document the methods each spindle OEM is using on each model that they manufacture. This gives us a comprehensive guide for the tolerances our grinding room needs to meet. Many spindle repair companies either do not grasp this concept or use outside vendors for their grind plate grind work and these important tolerances are not achieved. This definitely causes shorter spindle life and poor spindle performance.

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Rotary Union

The rotary union of a spindle is mounted to the rear of the shaft and it permits the movement of liquid from a stationary point into the rotating shaft. Typically rotary unions are used for the transfer of coolant in through tool coolant applications.

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The rotary union of a spindle is mounted to the rear of the shaft and it permits the movement of liquid from a stationary point into the rotating shaft. Typically rotary unions are used for the transfer of coolant in through tool coolant applications. They can also be used to transfer lubricant to the bearings in through the shaft lubrication systems (typically Makino machines).

There are several manufacturers of rotary unions with as many designs. Typically they use two ceramic disks that are separated when not in use but are pushed together by the pressure of the liquid when needed. These surfaces eventually wear causing leaks. On vertical spindles this causes the liquid to drain onto the rear of the spindle potentially causing bearing failure from contamination. It is very important to check the rotary unions on a regular basis and especially during spindle installation.

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What is a Rotor?

The rotor is the non-stationary part of the electric 3 phase induction motor system found in a spindle. It is part of the spindle shaft. It rotates because the wires and magnetic field of the motor are arranged so that a torque is developed about the rotor’s axis.

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The rotor is the non-stationary part of the electric 3 phase induction motor system found in a spindle. It is part of the spindle shaft. It rotates because the wires and magnetic field of the motor are arranged so that a torque is developed about the rotor’s axis.

Failures: Failures of this component are rare
Overheat: Excessive loads can cause a rotor to melt
Rotational contact: The rotor can be damaged by contact with stationary objects during rotation
Improper installation: Can cause the rotor to loosen from the shaft

Recommended repair procedure: The only fix for a damaged rotor is replacement.

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Preload of Angular Contact Bearings

Preloading bearings is the process of removing the internal clearance of the bearing by applying a permanent thrust load. This applied force makes the rolling elements run in a single “track” and it removes any axial play in the bearing assembly.

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Reasons for preloading bearings:

Eliminate radial and axial play in the bearings
Increase the spindles rigidity
Eliminates non-repetitive run out caused by bearing looseness
Prevents skidding of the rolling elements
If done incorrectly:

Excessive preload causes heat in the bearing drastically reducing its lifespan
Excessive preload increases the energy required to rotate the spindle
Under preloaded bearings cause the rolling elements to skid. This damages the raceways and the rolling elements causing premature failure
Under preloaded bearings cause looseness of the shaft resulting in poor part finish and the inability to hold tolerances.
Under preloaded bearings will often generate noise while the spindle is running
Methods of spindle repair bearing preload:

Install a duplex bearing set with previously adjusted stand-out dimensions and axial clearance
Use a spacer to obtain the correct offset
Use a force generated by spring tension
Use nuts to adjust axial preload by torque (This is a poor design for spindle applications)

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Oil Seals

Oil seals are a common way to reduce bearing contamination in machine tool spindle applications. They are used primarily in low speed applications because they make contact with the rotating shaft and have a limiting surface feet per minute specification.

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Oil seals are a common way to reduce bearing contamination in machine tool spindle applications. They are used primarily in low speed applications because they make contact with the rotating shaft and have a limiting surface feet per minute specification. They do eventually wear down. This wear is increased if contamination migrates into the contact zone. Grinding swarf is a good example of this. The rotating shaft can also be worn when this occurs. The shaft wear can be repaired with a grind plate grind or the installation of a speedy sleeve.

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I really didn’t expect this; You guys really pulled it off! My many thanks to Sandy, Louis and your outstanding crew for helping us get back into production.

Dan Eaton, Taylor Metalworks

Lou all in all everything is running good. Just had a call from Sandy just the other day, its funny great minds think alike. Its great not to be sending spindles out on a regular basis since you addressed my problems, but I know they will still be coming sooner or later. Never a problem when we get them back , run better than new. Hope everything is ok there. Please tell everyone there that we here appreciate everything that you do to keep us up and running and the quick turnarounds. Have delt with the rest now deal with the best. Have a great week end and up and coming holiday.

Northland Customer

Thank you Debbie just received spindle today and WOW ! what a nice job. Can’t wait to use it. Thank the Northland team for us for a job well done 

Northland Customer

Both of the spindles that you repaired are on the machines and running great. We don’t have any spares for those grinders. We probably will not be purchasing a spare, as you have been able to turn around the repairs quickly and the price of a spare is cost prohibitive.

Northland Customer

I am writing to thank Northland Tool for going the extra mile and saving my company from expensive machine downtime and expensive repairs. We have always sent our Chiron spindles for repair as a shaft with bearings. None of our previous rebuilders pointed out the bearing fretting or the fact that the housing in the machine was out of tolerance and causing premature failure to the spindles. After Northland fixed the housings the spindles have never sounded as good or run as well! Great job guys!

Northland Customer

The detailed cause of failure reports and the expert technical advice that Northland Tool provides is bar none the best I have ever seen. We struggled to keep two of our large our milling spindles running for longer than 6 to 12 months. Northland Tools evaluation showed that the hydraulic nuts were not holding the assembly together causing premature spindle failure. We discussed this in detail and mutually decided to modify the spindle shaft to prevent this from occurring again. The first spindle we performed this on is still in the machine running like new after 3 years. That’s over three times the life of previous repairs and it’s still going strong. Easily over $40,000.00 of savings so far on that one machine and counting.

Northland Customer

Your people go above and beyond the call of duty when it comes to spindle repair. When we had difficulty with the spindle installation and we were able to talk directly to a spindle technician that helped us troubleshoot the issue it helped us out of a bind. We have sent several spindles to you and have nothing but great things to say.

Northland Customer

Thank you for your attention with my quick turn spindle repair. Your status updates allowed me to plan around machine downtime and I now know that you deliver on your promises. In the past other spindle repair vendors talked a big game and consistently failed to deliver. You not only delivered my spindle before the due date but you kept me informed throughout the entire repair process.

Northland Customer

You performed a miracle with my BIG PLUS spindle. After crashing the spindle severely damaging the taper we found that a replacement spindle was not only cost prohibitive but had a long delivery. Your repair was a fraction of the cost of new and you never would know that the spindle was damaged to the extent it was.

Northland Customer

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