We hope that our Frequently Asked Question (FAQ) page will provide answers and insight to your spindle questions. We see this page as a work in progress. So please help us to grow and improve our FAQ page. If you have a question please send it to us. If you have an answer or a clarification on something we wrote, we'd like to hear from you. If you have a story that you think others can benefit from we may be able to publish it on our blog.
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Our question to you: How can we help?
High Speed Technologies is a service provider company. As such our product is not just repairing your spindle. We have an obligation to help you get the maximum life from your machine. Help us help you by sending in a question, a comment or telling us a story. We’re listening.
HST has the fastest turnaround time in the industry. We well know that a down machine means loss of income and possible loss of a job. However, there are some procedures that cannot be rushed. Even preparing an accurate quote takes many hours. As soon as your spindle reaches our shop, it is in our Forensic Engineering Quality Assurance (FEQA) program. Serial numbers are checked against our data base of over 100,000 repairs. The spindle must be completely disassembled and carefully inspected prior to quoting. This may take upwards of eight man hours. Once the spindle is thoroughly cleaned and inspected a firm quote is prepared, typically within 24 to 48 hours.
GPG is a time consuming process that many spindles require. Setting up for grinding involves meticulous precision. Grinding itself is a slow process and plating typically takes 14 to 25 hours for proper deposition. Once the spindle is fully assembled "running-in" a grease lubricated spindle may require up to 12 hours. Run-in is a process that cannot be rushed.
Typical non-GPG repairs take approximately 4-5 days after approval of quote. Spindles requiring GPG typically require 7-10 days for repair. Got to get it back right away? Ask for our QTA service.
If your spindle is in a production critical machine you can request our "Quick Turn Around" treatment. Your spindle is broken down immediately. Cause of failure and quotes are typically prepared the same day. All parts not in stock are expedited for "priority AM delivery". Typical QTA spindle turnaround not requiring GPG is two days. GPG may add an additional three to five days. There is a 15% surcharge for QTA service.
Note: QTA service is not always available.
HST has several goals for each spindle repair we do:
The first step is to log-in and check the spindle serial numbers against our data base of over 100,000 spindle repairs. Once logged in and photographed the spindle next goes to our breakdown and clean area. Here the spindle is completely disassembled and thoroughly cleaned.
Breakdown and Clean
Depending on the type and condition of the spindle, proper breakdown and cleaning can be labor intensive and time consuming. Taking apart a spindle may include cutting off seized nuts and pressing off rotors in our 100 ton press. Old paint is stripped off. All orifice and lubrication plugs are removed to get at minute internal passages that often harbor contamination. Scale and corrosion are removed from water jackets and cooling surfaces. Tapped holes are degreased, blown out and threads checked. Every spindle component is thoroughly degreased prior to inspection. Bearings and other components are examined to determine the cause of the failure.
Our customers will probably never see the inside of their spindle cooling jacket like this Okuma unit (below). However, at HST they are cleaned until they shine. The surfaces inside the jacket are critical for proper heat dissipation. Any scale or corrosion not removed negatively impacts the thermal transfer coefficient causing spindles to run hotter. Running hotter increases the likelihood of premature failure.
After cleaning, the components are moved to one of our examination benches. Because extreme accuracy is required, dimensional examination is conducted in an environmentally controlled clean area. All instruments used for measuring are calibrated to a certified set of gages just prior to each examination.
Once instrument calibration is verified, the following dimensions are examined and recorded*:
|Some of the shaft surfaces checked for TIR, concentricity, perpendicularity. Measurements are in microns.|
*Exact areas inspected depend on type of spindle. If the spindle is motorized all electrical components are checked for shorts, continuity and general condition.
The data is recorded, the components are photographed and the service report is updated. Only after this work is completed can an accurate quote be prepared for customer approval. The customer is under no obligation for any work completed prior to approval. Click Spindle repair costs for more information.
Once the repair is approved HST performs the following:
*The above description is a typical overview to provide our customers an idea of some of the work that goes into a typical spindle repair. The actual work and sequence can vary depending on the type and requirements of a particular spindle.
Bearing journal dimensions are critical. For maximum life and spindle performance worn journals must be restored to manufacturer's specifications. If your spindle has worn journals, out of tolerance shaft taper or other worn dimensional critical areas these may require "Grind-Plate-Grind".
Worn areas are first ground to a uniform undersize dimension. This is the first "Grind" often called a "green grind". The part is then hard plated to an oversize dimension. This is the "Plate". After plating, the part is re-ground to the exact nominal dimension; the final "Grind" of GPG.
HST works with tolerances to +/- 50 millionths of an inch (.00005") to make sure your precision bearings have a precision fit. Once ground to size, rotating components are rebalanced to ISO 1940/1 G0.4.
Often a spindle requires a "kiss" or "breeze" grind. This is a light grinding that does not require subsequent plating and regrinding. Just enough material is removed to correct minor imperfections. This is most often done on ID tapers and shaft faces to ensure perfect tool holder interface.
If the spindle taper does not exactly conform to the tool holder taper, the tool may be able to move slightly. This can cause poor part quality and bad tolerance. A perfect match is an absolute must for high quality machining. Verifying taper quality at HST is SOP.
That is one of the first questions we hear from new customers. To provide an accurate price quote we need to know the extent of the damage. There are many factors that affect the ultimate cost of a spindle repair. Is it only a failed bearing? Does it need GPG? Is the draw bar damaged? What is the journal TIR? Are the journals within spec? Is the housing within spec? The dimensional tolerances for high precision bearings are measured in less than 1/10,000 of an inch. These and many other aspects of the spindle are examined before an accurate repair cost is known. When HST quotes a repair, that is the number we stick with. We never "bait and switch".
None the less, our customers often ask for an estimate before they ship the spindle. Any estimates provided prior to our examination of the spindle are provided in good faith to help our customers get a feeling for the range of cost that might be encountered. We want our customers to be aware that the cost of a comprehensive repair can be more than double that of a "basic" repair. While our quotes are firm, all good faith estimates are subject to change.
All of our quotes are no obligation and free of charge. So, the best bet is to send it to us for examination. Your spindle will be broken down, cleaned, examined and critical dimensions measured. If you decline to have the spindle repaired, we will return the cleaned parts free of charge. All components will be photo documented. Note: it is often impossible to re-assemble catastrophically damaged components. In cases where the repair is declined and reassembly is impossible the spindle will be returned disassembled.
HST developed the FEQA program to take Quality Assurance to another level of customer service.
Forensic Engineering is the investigation of components that fail or do not function as intended. Our purpose for forensic engineering is to locate the cause of failure with a view to improving the performance or life of the spindle.
Quality Assurance is defined by ISO 9000:2000 as "providing confidence that requirements will be met". It is our systematic plan of action necessary to provide adequate confidence that your spindle will perform up to OEM specifications. Quality assurance includes quality control.
Combining these in our FEQA program we not only examine our in-house procedures for providing top quality repairs; we also look at the cause of failure with a view toward helping our customers improve their operations and increase spindle life. This can result in less down time and higher production for our customers.
In our data base of over 100,000 repairs we have seen a broad spectrum of failures. Some failure causes include:
*Not applicable to fluid element spindles (air bearings)
One of the most common types of bearing failure is contamination. Contamination includes all foreign substances as well as water. Sources of contamination include:
If an air-oil lubrication system is used, clean dry air is an absolute must for long spindle life. The lubricant must likewise be clean and free from moisture. Besides system air driers and filters, HST recommends separate coalesors (or desiccant) driers along with 0.5 micron air filters on the airline immediately ahead of the oiler.
To prevent ingression through shaft seals it is imperative that these be properly installed and maintained. Avoid directing tool coolant at shaft seals. Additionally, chips and debris should not be allowed to build up to the point of contacting the shaft seal.
Use only high quality filtered lubricant. Inspect and certify that the container and all transmission lines are uncontaminated.
To avoid "built-in" contamination, all spindle and bearing assembly should be carried out in a class 10,000 clean room.
Spindles may look rather sturdy. However, the precision bearings inside rolling element spindles are very susceptible to mishandling. The bearing sets are preloaded so all forces on the shaft are transmitted through the rolling elements. Either radial or axial impacts to the spindle shaft can cause Brinelling with subsequent rapid deterioration of the bearings condition. External vibration may cause what is referred to as "False Brinelling". This condition also precipitates rapid deterioration. Never strike a spindle. Never transmit static force through the rolling elements. Always protect spindles from vibrations. Shafts on fluid element spindles should never be rotated unless the spindle is properly "floated". When installing pulleys or other devices on the shaft always take time to properly support the shaft.
A common indication of a crash is Brinelling. Whereas false Brinelling and Brinelling that results from mishandling often requires microscopic examination to make an accurate determination. A crash often leaves indications that are very visible to the unaided eye.
Bearings must have the proper amount of preload for maximum life and optimum performance. Too much preload and the bearing will fail in a similar method to overloading. Insufficient preload and the rolling elements "skid". Skidding also results in premature failure and poor tool performance.
Although it is always best to size your spindle for the job, in many cases HST can retrofit your spindle for higher load and speed capacity. Most often operational parameters can be increased by using hybrid bearings. Lubrication is another factor to consider. We will be happy to provide recommendations and a quote to increase your spindle capacity.
The correct type and the correct amount of lubricant are critical to spindle life. Most lubrication failures in our data base are associated with Oil Mist and Air/Oil. One of the key factors with airborne lubrication systems is an adequate supply of clean dry air. HST always checks all porting and orifices on every spindle housing to verify unobstructed flow of lubricant to bearing.
Shaft or rotating mass imbalance not only impairs production quality it can also precipitate premature bearing failure. HST balances all shafts and rotating components to ISO 1940 G0.4.
Drawbar failures include actuators, dogs, Belleville springs, gripper arms and a host of other components. HST repairs them all. Spring force is reset to OEM standards. All components are balanced and tested.
Statistical Bearing Failure
All bearings have a L10 (or B10) life. This is a statistical life span that when operated under a rated load condition 10% of the bearings will fail. Some of these bearings may fail sooner and some may fail later. In either case the bearing manufacturer expects that 90% of the bearings will still be operational after the L10 life. Most spindles are engineered for bearing life that far exceeds the L10 rating of the bearings. That having been said, there is always a non-zero statistical likelihood of any bearing failing at any time regardless of how good the installation is.
Today there are many excellent lubricants for the full spectrum of spindle applications. The OEM should always be the first source for lubrication requirements. However, if that information is not available HST makes the following recommendations.
There are three primary components to precision grease lubrication for bearings:
The quantity of lubricant or "fill" is a function of the rated spindle speed. In grease lubricated spindles it is critical the precise amount of lubricant is applied; not too much, not too little. Extreme caution should be exercised to maintain the highest qualities of cleanliness. HST precision lubricates all grease spindles in a separate "mini clean room".
Several manufacturers have recently introduced new formulations specifically blended for very high speed spindle applications. Kluberspeed 72-22 is HST's default lubricant for all high speed grease lubricated spindles. Barden - Arcanol L75 is the same excellent lubricant privately labeled. Both of these lubricants work well with steel and ceramic hybrid bearings. Although most grease applications are for speeds below 600,000 dN, these new greases are formulated for ultra high speeds up to 1,500,000 dN.
All grease spindles must be "run-in" to avoid subsequent lubricant related failures. This is a process where the spindle is operated at incrementally increasing speeds. Spindle temperature is carefully monitored during run-in. The spindle cannot be accelerated to the next speed increment until the temperature "breaks". Incorrect run-in can cause the grease to be pushed away from the bearing track and result in a premature failure.
Proper Run-In is required to:
Run-in can take in excess of 12 hours depending on the speed and nature of the spindle. This is a procedure that cannot be rushed.
HST uses Mobil DTE oil lubricants. However, as with grease there are a number of fine oil lubricants on the market. The following ISO standard viscosities are recommended by bearing manufacturers:
Imbalance is caused by the displacement of the mass centerline from the rotational axis which is a function of eccentricity in the distribution of the rotor mass. It is measured in units of mass and distance, e.g., gram-millimeters or gmm. Imbalance is considered in single plane modes and dual plane modes.
Balancing is the correction of this mass displacement by the removal, addition or adjustment of mass to the component to compensate for centerline error. Most high speed spindles are balanced by the appropriate removal of mass. Some larger machine tool spindles have pre-drilled and tapped holes for the addition of set screws which facilitates the addition of mass to compensate imbalance.
There are two general forms of balancing: "Static" and "Dynamic". Static balancing (which is not really static) involves installing the component into a balancing machine and measuring the "heavy" point in relation to the centerline, while the part is rotating. If the required balance correction is at a single axial point on the rotor the balance is said to be "Single-Plane". Single plane balancing is adequate for rotating bodies with a low length to diameter ratio (l/d).
Dynamic or "Dual-Plane" balancing is required for components or assemblies of significant length. Rotors with some axial length can have two "heavy" points at opposing ends of the component, acting independently on the mass center line. In order to balance the component, both planes must be corrected for center line error. Dynamic balancing is required for components such as shafts and multi-rotor assemblies.
The rotating components are balanced and assembled into the spindle. Often certain components are attached to the spindle shaft after assembly into the housing. At this point there may be some residual mass imbalance. This imbalance is compensated by trim balancing the completely assembled rotating group. Usually imbalance is measured while running the spindle at full operating speed. Running at full speed allows for the finest tuning to be accomplished.
Often high end spindles have a series of tapped holes around the periphery allowing the addition of various sized set screws. Appropriate installation of these set screws allows a trained technician to virtually eliminate the effects of residual imbalance.
ISO 1940/1 is an international standard used for qualifying the balance of rotating rigid bodies. G0.4 is a particular balance grade within the overall standard. Compliance with this standard requires that the maximum residual imbalance falls within certain limits dependent on the overall mass of the rotating body. Grade G0.4 is on the finer end of the spectrum and typically the qualifying range for high speed precision spindles.
Some standard ISO grades and their applications are listed below:
Our balancing machines are calibrated using standard rotors traceable to NIST
ABEC ratings have to do with the quality and precision of the bearing. ABEC 7 bearings are also referred to as "Super Precision Bearings" and are equivalent to ISO P4. These bearings are specifically designed for machine tool applications. Typically they are purchased in matched sets or quad sets. HST always uses ABEC 7 or ABEC 9 (Super High Precision, ISO P2) bearings.
When assembling Super Precision Bearings the manufacturer matches the balls to the races using a very tight tolerance. Although assembled on high speed equipment each Super Precision Bearing is a "custom" assembly. Each race is individually measured to better than 1 µm and then assembled with balls that exactly match the race variation. That is just one of the factors that influence the price of the ABEC 7 bearings. It is not uncommon for bearings in a medium size spindle to cost over $2000.
HST uses matched set bearings. These are bearings that are ground together in the same operation. There is a move in the industry to use P4Y or equivalent bearings. These bearing are universally ground to very tight tolerances. In theory, deviation from any individual bearing to any other bearing is within the tolerance for a matched set. Prior to assembly our technicians test each bearing set to verify proper loading. Our technicians have had several P4Y bearings sets that have not passed their scrutiny. Our bearing suppliers complain that we reject more bearings than all their other customers combined. Well, the customer sees our name on the repair not the bearing manufacturer. None the less, manufacturing processes continue to improve and we believe that matched sets will be phased out in favor of P4Y bearings or similar designation. In any event, HST will continue to test and inspect every set of bearings that we receive to make sure they are within our tolerance. We will only use the finest components available.
Proper preload maximizes bearing life and optimizes machine performance. Bearing preload influences speed limits, rigidity and other applicable workloads.Different types of bearings are preloaded in different ways. However, the most common adjustment affecting spindle repair is the axial preload required for angular contact bearings. If bearing preload is too light the spindle will lose rigidity and might experience ball skip. This can lead to poor part quality and premature failure. Excessive preload can result in excessive heat buildup and premature failure. Getting preload exactly right is a must for proper spindle performance and long life.
Preload is the load generated from the axial interference within a bearing resulting in elastic deformation between rolling elements and the raceway. In other words, preload is the amount of force exerted against the rolling elements without the application of any external forces. The two primary types of axial preload are referred to as Rigid Preload and Elastic Preload.
Rigid preload involves generating an interference fit between the faces of opposite bearings when bearings are locked axially. It may change due to thermal expansion. Two ways to control the amount of interference (i.e., pre-load) are by a threaded adjustment or precision ground spacers. In either case, these settings can be critical to less than 2 microns (.000078"). Many of the "high-end" spindles such as Okuma, Mori-Seiki, Niigata use rigid pre-load. Setting rigid preload requires know-how and skill. Engineering consideration must be given to dimensional changes resulting from thermal expansion and/or contraction.
Elastic preload is generated by a series of springs reacting against the bearings in the axial direction. Thermal expansion is compensated for by the springs. Bearing preload variations are minimized in this configuration. Care must be given to match the individual springs to avoid uneven loading.
Below is our formal warranty. Simply put our intention is to provide the best possible spindle repair. If we did something incorrect we will repair it as fast as possible and make good as best we can. We exist because of our customers. They deserve the best we can provide.
Before we get to the legalese, let us speak a little in layman’s terms about warranties. All warranties are for a specified period of time. Our warranties are for workmanship and the parts that we install. We want our customers to receive the very best repair possible and if for some reason our workmanship is deficient we want to make good on it.
The warranty period varies depending on the type of spindle and the nature of the repair. As a general case our warranty period for the different spindles is as follows:
The warranty period for a specific repair is noted on the Quality Assurance Report provided with each repair.
High Speed Technologies (HST) warranties our spindle repairs against defects in parts and workmanship for a period of time specifically stated on the Quality Assurance Report (QAR) provided with each individual repair. In no case shall our warranty extend past one (1) year form date of repair or exceed the original manufacturer’s warranty period unless specified in the QAR for the particular repair. This warranty is limited to parts replaced or services performed. This warranty does not cover damage caused by improper installation, crashes, contamination, lack of lubrication, improper use or application, failure to follow manufacturers operating guidelines or damage during shipment. HST shall have final and binding discretion to determine validity of any warranty claims and any other dispute, controversies, or interpretation arising hereunder.
LIMITED WARRANTY. In lieu of all other warranties, express or implied, including without limitation warranties of merchantability and/or fitness for a particular purpose, High Speed Technologies, Inc., Inc. issues only to Customer (and not to any subsequent owner of the repaired item or other person or entity) this limited warranty for spindles repaired by High Speed Technologies, Inc. pursuant to a purchase order accepted by High Speed Technologies, Inc.:
High Speed Technologies, Inc. warrants that each spindle repaired, when it leaves High Speed Technologies, Inc.’s repair facility, will conform to the original manufacturer’s specifications unless noted otherwise on the QAR; and warrants that each spindle repaired will, for a period specified from the date of such repair, be free of defects in workmanship and material or parts used or installed by High Speed Technologies, Inc. in completing such repair, subject in each case to the following conditions and restrictions:
Customer must follow the warranty claim procedure described below.
High Speed Technologies, Inc.’s liability under this limited warranty shall be either to repair the nonconforming or defective spindle or to reimburse to Customer the cost of the High Speed Technologies, Inc. repairs, at High Speed Technologies, Inc.’s sole and absolute discretion.
HIGH SPEED TECHNOLOGIES, INC. SHALL NOT UNDER ANY CIRCUMSTANCES BE LIABLE FOR INCONVENIENCE OR LOSS OF USE OF THE SPINDLE OR ANY MACHINERY, EQUIPMENT, APPLICATION OR PROCESS OF WHICH THE SPINDLE IS A COMPONENT OR PART, AND SHALL NOT UNDER ANY CIRCUMSTANCES BE LIABLE FOR ANY DIRECT, INDIRECT, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES, COSTS AND/OR EXPENSES ARISING OUT OF THE USE OF THE SPINDLE OR THE FAILURE OF THE REPAIRED SPINDLE TO CONFORM TO THIS LIMITED WARRANTY, REGARDLESS OF THE THEORY OF LIABILITY UNDER WHICH ANY SUCH CLAIM MAY BE PERSUED. HIGH SPEED TECHNOLOGIES, INC.’S LIABILITY SHALL NOT, IN ANY EVENT, EXCEED THE AMOUNT CHARGED BY HIGH SPEED TECHNOLOGIES, INC. TO CUSTOMER FOR THE REPAIR SERVICES.
High Speed Technologies, Inc. shall not be liable to Customer or any other person, and this limited warranty shall be void, if Customer or any other person: (a) modifies, tampers with or attempts to repair the spindle after High Speed Technologies, Inc.’s repair or (b) uses the spindle in a manner other than as recommended by the manufacturer, or (c) uses the spindle in any machinery, equipment, application or process for which the spindle is not rated by the manufacturer, or (d) if the claimed failure of a repaired spindle is the result of misuse, neglect, abuse, accident or the failure of any other machinery or equipment, or component thereof. If Customer’s spindle remains subject to any manufacturer’s warranty as of the date Customer’s warranty claim arose, Customer agrees to make such claim under the manufacturer’s warranty, and agrees that the manufacturer’s warranty shall supersede High Speed Technologies, Inc.’s limited warranty, which shall not be applicable; however, High Speed Technologies, Inc. may in its sole discretion, but only if authorized in writing by the manufacturer, perform repair services to Customer’s spindle.
If an item repaired by High Speed Technologies, Inc. is claimed not to conform to the original manufacturer’s specifications when it is received by Customer, or is claimed to be defective within the limited warranty period, Customer shall give prompt written notice to High Speed Technologies, Inc., and in no event later than that expiration of the limited warranty period. Customer shall be responsible for any shipping and handling or similar costs for return to High Speed Technologies, Inc. of the repaired motor. Upon receipt of the motor, High Speed Technologies, Inc.’s technicians will inspect the item and determine whether the claimed non-conformity or defect, as the case may be, is related to the High Speed Technologies, Inc. repair.
High Speed Technologies is very proud of our warranty and we stand four square behind it. The caliber of our technicians and the quality of our test procedures give us confidence to make this stand. However, our warranty does not cover failures due to mishandling, improper use, lack of or improper lubrication, or contamination.
Prior to shipping a spindle HST runs-in each spindle and logs vibration analysis on one of our Vitec Analyzers. This information is part of the permanent record maintained in our data base. Each analyzer is certified. The calibration is traceable to NIST and compliant with MIL-STD 45662A. After run-in, each spindle is run to speed and analyzed for balance, noise, proper preload, Brinnelling, dynamic run-out and heat build-up. When we ship, we are certain that the spindle meets or exceeds OEM specification.
In our FEQA program the spindle is dismantled and examined. Most often there are tell-tale indicators for the cause of failure. A few of the indicators in rolling element spindles include:
Likewise fluid element spindles are reviewed in our FEQA program and have their own set of tell-tale indicators.
If any of these indicators are present, the spindle is subjected to a second review. After the second review a determination is made concerning warranty. In every case the customer is provided photo documentation and an explanation of the cause of failure. We are always open for discussion and try to assist our customers in every way possible to avoid premature failures.
The short response to that question is “probably not”. It is true that machine shops make precision parts: they are used to working with tight tolerances and many have skilled and capable machinist. So why do they use a qualified spindle repair shop like High Speed Technologies (HST)? There are a number of very good reasons.
First, most modern machine shops work with tolerances in the range of +/- 0.013mm (0.0005”). To repair a modern spindle that can consistently provide parts with that accuracy our tolerances are an order of magnitude tighter. Super Precision ABEC 7 spindle bearings have tolerances called out in the +/- a few microns. So the technicians at HST must consistently work in the micron range (0.001mm).
To provide those tolerances a climate controlled assembly area is required. When setting spacers our technicians must take into account that the heat from their hands can affect the dimensions of smaller gage bocks. Grinding and finishing of journals requires additional time for parts to reach thermal equilibrium. Spindles received from air delivery services may take many hours to reach room temperature before accurate measurements can be taken.
Additionally, HST technicians have “bearing know-how”. They understand spindle bearing theory; why some are mounted “back to back”, “tandem”, with spacers and without. They understand lubrication requirements, journal fits and assembly procedures. They are experts at grinding and sizing spacers to achieve the correct critical required preload. Our technicians handle and set your bearings with extraordinary care and precision. They know that one bad move can trash an expensive pair of spindle bearings.
HST technicians have “spindle know-how”. They understand how to set draw bar tension and actuator settings. With calibrated tension gages they will set your drawbar tension back to OEM specifications.
HST technicians have “balance know-how”. Vibration caused by spindle imbalance cannot be tolerated when machining precision parts. It affects part finish and spindle life span. At HST no spindle is shipped until it passes stringent balance and vibration testing.
Cost is another good reason to use a qualified spindle repair house like HST. When you consider that the bearings make up between 30% - 40% of the cost and other components up to 15% you are left with about 50% for labor and margin. So how much can you save by doing the spindle yourself; probably nothing. Spindle repair is our core business. That’s what we do.
When it comes to repairing spindles we recommend you don’t try this at home. Leave it to the trained professionals.
Perhaps. But there are many factors to consider when replacing the bearings on a machine tool spindle. Whether the balls are ceramic or steel is not necessary the most important component. Also, it is important to keep in mind that while ceramic bearings are typically rated for 20% higher speeds, they also have lower load capacity.
When our technicians calculate maximum operating speed they consult design specifications provided by the bearing manufacturers. These specifications will include several considerations and they all factor into the speed algorithm.
The preload affects spindle stiffness as well as maximum operating speed.
Various configurations affect spindle stiffness as well as operating speed. Are the bearings mounted back to back? Is there a tandem component?
Each bearing assembly will have a different speed rating for the type of lubrication used, e.g., grease, oil mist, injection, etc.
Smaller balls have less mass so they can spin faster. But they are not available in all configurations. Big balls can handle more load.
Thermal Transfer Coefficient
All bearing generate heat when turning. How much heat will they generate and how fast can that heat be dissipated through the spindle housing.
Like so many things in life there is no free lunch. So when a spindle repair house promises you 20% higher speed by slapping in a pair of ceramic bearings you may want to ask what the trade off is. Will my spindle fail sooner? Can I live with the reduced load capacity? And ceramics are always more expensive.
If your spindle load is light to moderate and increased speed will provide increased production and profit, ceramics may be a good idea. However, make sure your spindle repair house does their homework before they promise you 20% higher speeds.
At HST we will be happy to change out your steel ball bearings for ceramic. But before we do, we'll make sure the homework's done.
Tom M. a maintenance supervisor at GSO &M sent us the above question.
The short answer to this question is not very long at all. In fact, a fully loaded roller bearing operating at its nominally rated speed with no lubrication will fail immediately. This is true for any rolling element bearing properly installed and loaded. We won't ask how an installed bearing came to have no lubrication.
Please let me explain a little of why the bearing will fail without lubrication and hence the importance of proper lubrication. Obviously a roller bearing consists of two races an inner and an outer with rolling elements (rollers) in between. The distance the roller rolls on the outer race is longer than the distance the roller has to roll on the inner race. For that reason the rolling element must slip somewhat on one or both of the races to compensate for the difference.
The lubrication provides a film on which the rolling elements can slip. The steel on steel coefficient of friction is very high so without the lubrication film the friction between the steel roller and the steel race is so high that it can cause the steel to gall or tear. This can happen immediately.
Bearing ratings (speed, load) and preload settings are affected by the type of lubricant and the method of lubrication. Grease lubricated bearings normally run slower and handle higher loads. Oil mist or oil injection bearings run at higher speeds. Exceeding the load rating can have a similar effect as no lubrication. In a high load situation the rolling element can pierce the lubricant film and generate a metal to metal contact and cause the race to tear.
Another factor that can result in a similar type of failure is water contamination. A minute amount of water can displace the oil film in places on the race. Where that happens, the rolling element will make contact with the race with the resultant tear or galling effect.
These two photos show different modes of failure. However, in both photos race deformation is evident.