CNC EQUIPMENT DIAGNOSTICS AND MAINTENANCE INFORMATION
CNC (computer numerically controlled) machines are costly high precision machines for basic manufacturing industries such as primary metals (steel,aluminum etc.),electronics and computers, aircraft and defense , plastics ,telcom, automotive and more. Almost everything that is manufactured anywhere can
be traced back to a cnc machine. Yet people routinely abuse and ignore maintenance on these $50,000 to $3,000,000 and up machines. This site will try to help you with what is really important and avoid costly mistakes others already have made.
The following page will describe many common CNC problems and recommend solutions to them.
They will be indexed alphabetically by the subject. Hard to find parts info will be added soon.
DISCLAIMER!!! USE THIS INFORMATION AT YOUR OWN RISK. IT IS HIGHLY RECOMMENDED THAT YOU CALL IN A TRAINED ENGINEER OR TECHNICIAN TO WORK ON THIS EQUIPMENT. THIS ADVICE IS GENERAL AND I CANNOT BE HELD RESPONSIBLE FOR ANY INCORRECT INFORMATION. I ALSO CANNOT BE HELD RESPONSIBLE FOR INJURIES OR DEATH CAUSED BY YOUR ATTEMPTS TO SERVICE THIS EQUIPMENT. USE OF ANY, PART, AND / OR ALL OF THIS INFORMATION AT YOUR OWN RISK!! THE EQUIPMENT IS INHERENTLY DANGEROUS AND MAY RESULT IN
MECHANICAL INJURY SUCH AS CRUSHING, CUTTING OR SEVERING OF LIMBS. YOU MAY FALL OFF MACHINES DUE TO OILY SURFACES OR DANGERS UNFORSEEN. IT ALSO MAY RESULT IN ELECTROCUTION FROM INTERNAL OR EXTERNAL HIGH VOLTAGE CIRCUITS. NEVER ENTER ANY ENCLOSURE OR AREA WITHIN THE MACHINE STROKE WHILE UNDER POWER! CONTINUE AT YOUR OWN RISK!!!
1) AUTO TOOL CHANGERS 2)ALIGNMENTS 3)ALARMS 4)4TH (B) AXIS 5)CONTROLS 6)COUNTERWEIGHTS 7)COOLANT 8)COMMUNICATIONS 9)DISPLAYS 10)ELECTRICAL SYSTEMS 11)LEVELING AND INSTALLATION 12)MACROS AND DEBUGGING 13)SERVOS AND DRIVES 14)SPINDLES + BEARINGS 15)SUMMER MAINTENANCE
A_ AUTOMATIC TOOL CHANGERS- almost all modern CNC machine tools have this semi-robotic device known as a tool changer. It is a major trouble spot on many machines. Needless to say it should be kept clean and lubricated.
It also should be recognized as one of the worst offenders regarding possible injuries. It doesn't really want to hurt you, it just doesn't know or care that you are there!! So if you are doing any work on an ATC UNIT MAKE SURE
THAT THE MACHINE IS IN AN EMERGENCY STOP MODE. UNPLANNNED MOTIONS CAUSED BY LIMIT SWITCHES SUDDENLY COMPLETING A CIRCUIT MAY CAUSE THE CYCLE TO CONTINUE!!! If you have to frequently beat your tool arm with a hammer you really should stop and assess the
situation. (I know it feels good to hit the machine but it may hit you back or throw a tool at you!) The entire tool change process should be a smooth, fluid motion and should not make any grinding popping or other insidious noises. The arm or carousel should not flex, bend, or distort.
If the function stops in the same place all the time you either have a bad alignment, bad solenoid, bad limit or proximity switch or a broken spring. If it drops tools you may likely have broken pins, springs, a bent arm or worn fingers. You can adjust the speeds if the unit is air or hydraulically driven by turning throttle valves on the solenoids on most machines if the motion seems too fast or slow.
Look carefully at the entire mechanism and observe operations many times before deciding what to do. Do not attempt to speed up an older unit beyond it's rated speed or you might get a 30 pound tool tossed on your shoes!
If it is CAM DRIVEN (OKK) the only thing likely to break is a cam follower. The part is relatively cheap (the labor is not). Most of these have an inverter drive system which can be adjusted by parameters on the unit. Again, use caution regarding speed and stability.
Older tool changers are driven by a rack and pinion system that is almost universal. The pot comes dowm from the magazine. It is confirmed by a LS(limit Switch)and the spindle orients- then the arm moves 60 degrees(72 degrees) to under the spindle. It also is LS confirmed.
If the arm pushes the spindle wrong it can lose the orient signal and stop. Should that be ok, the tool unclamps(again confirmed by LS) and the arm down is commanded. It gets LS confirmed and then the 180 motion is done. When it is confirmed the arm goes up. That too is confirmed
and the arm goes back to home(60 or 72 degree back). That too of course is confirmed but remember the 180 degree motion? It also has to go back but you won't see that happen since the arm is not engaged in the 180 degree rack. But if this does not happen the machine won't run. If it does,
the pot should go up to the magazine but this can be simultaneous depending on the MFG. So you know the motions, most machine have a standard procedure to return the arm home. LOOK IT UP! it will keep you out of trouble if you avoid pushing solenoids and if you really have to do it make sure you know which one is which and
the right sequence of events. Remove tool holders if possible to prevent damage or injury and keep people away when testing!!!
Whether it is an arm type or a carousel type they all have their inherent problems. Carousel type (umbrella type) are the simplest and also the slowest type of tool changer. Usually they are air or hydraulic(HAAS uses motors)
operated and have a manual switch or "M code" to return them to home. If all else fails these can usually be pushed home manually if the air is disconnected and if it's hydraulic you can push the CORRECT solenoid after you verify the procedure. When in doubt call the mfg. service dept.
For Arm type tool changers things get a little more complicated but there is usually a procedure to get everything back to where you started. NEVER RANDOMLY PUSH SOLENOIDS ON HYDRAULIC OR AIR OPERATED ATC ARMS. You can damage parts, throw tools and get the sequence out of order in such a way that you WILL need
assistance to recover. You should only operate solenoids as a last resort. Follow the procedures in your manuals, which may use m codes or some switches to return home. Some newer machines (OKK) have a cam operated ATC which is very fast, this type has a PLC switch to get it home by turning on the switch on the parameter screen
and holding in the ATC button. On some vertical machines you'll need to command a M102 to get the tool pot home afterwards. There also is a way to drive the cam manually by turning the drive motor fan etc.
When a tool changer fails it is very important to note EXACT alarm
codes and where the arm is stopping. And also be sure to check if the tool clamps tightly in the spindle. If it does not you either have the wrong retention knob (pull stud) or broken/loose belleville washer stacks in the spindle drawbar assembly. THIS CAN BE VERY DANGEROUS SO CHECK WITH A PROFESSIONAL!!
A- ALIGNMENTS. All machines have critical alignments on leveling, tool changers,pallet changers, turrets, tailstocks and many other
areas. They are covered under their specific names. For example under leveling it will be explained that some machines are designed with
a deliberate amount of flexibility in the iron base casting to allow for slight adjustments to bring the spindle in line with the table,
while others have a rigid base that cannot be adjusted. The procedures for both will be covered.
ALARMS_ PLEASE TAKE THE TIME TO WRITE DOWN THE ENTIRE ALARM AND RELATED MESSAGES AND PRECISELY WHEN THEY OCCUR. VAGUENESS SLOWS DOWN ALL DIAGNOSING AND REPAIR OF PROBLEMS!!! IF IT HAPPENS ONLY WHEN SOMEBODY STARTS THEIR FORKLIFT OR FERARRI TELL US BECAUSE IT'S ALL RELEVANT INFO! Then check your manuals before calling for service!
B- B AXIS- Some vertical machines may refer to it as an A axis but the rules are the same. Most HMCs have a standard B axis which allows indexing but not cutting
unless it is a "full 4th axis". The difference is that the full 4th does not have a curvic coupling( a large ring consisting of two halves which is precision cut to guarantee
that every time you clamp it you have an accurate position). The full 4th axis is always the more expensive option becauase it requires a larger servo motor and a tougher, more precise
worm gear that will withstand the stresses of active loads. You should never have a huge offset load(a load that is more than a few inches past the edges of the table outside diameter) or you'll wear out the worm gear. The biggest problem with both types are contamination of the gearbox with water soluble coolants which corrode the gears and can
short ot the servo motors. Other problems are limit switches for table clamp, unclamp, zero return, and if the table has a rotary feedback encoder(expensive and difficult to replace or repair)
You will want to keep your gearboxes filled with gearlube(see the manuals) and make sure there is no coolant getting in. Otherwise the unit WILL be destroyed by rust and corrosion. This is probably the
biggest problem on 4th axis tables.
C-CONTROLS AND CIRCUITBOARDS FIRST WRITE DOWN ALL ALARMS AND EXACTLY WHEN THEY OCCUR, WHAT LEDS ARE ON, WHAT OTHER SYMPTOMS HAVE BEEN DISPLAYED. If the night guy says sparks fly out of that component around 2:25 am every night we need to know this to help you.
Turn off power before checking! There are many times that you can "swap" a board with another machine provided you take some precautions. First make sure the revision numbers are swappable and the software is a compatible version. Be prepared to lose parameters programs and offsets whenever you pull a board, which means write them down or send them to disk.
I prefer a written or printed hard copy.Then examine the suspected bad board. Make sure it is clean. If there is obvious damage (smoke, flames, melting, piles of components falling off) you can safely assume this is where your problem is. Otherwise do not jump to conclusions. Before swapping, check if all socketed IC chips and eeproms are indeed firmly seated and no
legs are bent on chips. Look for bad solder joints. Take off all connections, clean the board(with dry air or electronic cleaner DON'T OVERCOOL THE BOARD WITH CLEANER!!! DANGER!! MAKE 100 PERCENT SURE THE FLUID HAS EVAPORATED. SOMEONE RECENTLY POWERED UP A SEQUENCER SOAKED IN CLEANER AND IT CAUGHT FIRE AND MELTED! REPLACEMENTS WERE NO LONGER AVAILABLE !! Reseat the board and power it back up to see if problem still exists. (you did power it down, didnt you?) Generally if the problem is gone you are ok.
If not you'll have to do the swap provided you have more than
one machine. If the problem moves you're board is bad. If not KEEP LOOKING or call for help. But please NEVER PUT A BOARD IN THE WRONG SLOT OR WORSE UPSIDE DOWN!!! THIS IS A FATAL ERROR AND WILL COST YOU!! And always check all cooling fans especially during hot weather both inside and out of the cabinets, behind amplifiers. And as I repeat below
NEVER SWAP ANY DRIVE BOARDS WITH OVERCURRENT OVERVOLTAGE OR DISCHARGE ALARMS. THIS CAN CAUSE FURTHER DAMAGE TO DRIVE BOARDS FIRING CIRCUITS AND BASE TRANSISTORS/ SCR'S. IN THESE CASES CHECK MOTORS AND CABLES, OHM OUT MOTORS TO GROUND, AND LOOK FOR COOLANT AND CHIPS IN THE CABLES THEN SWAP WHOLE AMP IF UNIT IS SAME - SET ALL NECESSARY JUMPERS AND WRITE DOWN THE ORIGINAL SETTINGS. WHEN IN DOUBT CALL FOR HELP!!
and PLEASE MARK ALL UNMARKED CABLES AND WIRES BEFORE YOU TAKE THEM OUT. ALSO NEVER PLUG SOMETHING IN JUST BECAUSE IT LOOKS LIKE IT SHOULD BE PLUGGED IN. IT COULD BE FOR SOME UNUSED OPTION AND MAY SEND HIGH VOLTAGE TO GOD KNOWS WHERE AND REALLY REALLY COST YOU!! AND LASTLY DO NOT TRY TO CHANGE PARAMETERS IN ANY CONTROL THAT YOU ARE NOT SURE WHAT THEY ARE FOR. DO NOT GUESS!
COUNTERWEIGHT CHAINS RECENTLY WE HAVE SEEN A LOT OF CHAINS ABOUT TO BREAK. I highly recommend inspection of all chains on machine vertical axis(Z AXIS on VMC's) because if it breaks the weight will fall down and cause damage to ballscrews , covers and anything below the weight including the machine casting.
If the chain groans, squeaks ,is rusty or rubs anywhere replace them ASAP. Keep them lubed and count the links on the old chain , use the exact same type of chain, and never go by the length of the old chain. If you measure the old chain you will surely find it has "grown" up to 3 inches from the original length.
If you hear a "clunking" sound when peck drilling or zero returning a machine chances are the chains or rollers are no good.
COOLANT tanks: another area where lack of maintenance shows up is in the coolant tank. If you have a smell that makes you gag when the pump comes on it is caused by aerobic and anerobic bacteria that grow in the tanks
and changes the chemistry of the fluid, making it corrosive. This can cause other parts of your machine that are indirectly exposed also corrode. The vapors are also unhealthy to breathe!!.
So clean the tanks often and Skim any way oil off the top(this feeds the bacteria). If coolant is getting into any electrical area, make sure you dry out the cables and connectors well and seal it up before continuing running!
COMMUNICATIONS - Most modern machines are now offered with a direct ethernet card interface so the machines can be networked to any pc or server in the building. We are experts in this field, contact us for a consultation. Cable lengths should be kept to a minimum for reliability. Tbase10 in a shop environment can be up to 100 feet or so if you keep it away from motors or
high voltage equipment. ALL machines have at least a RS232C port for serial communications which usually are limited to 9600kbps by the control mfg. At 9600 you can be up to 30 feet away. If your programs are short and your cable long you can go down to 2400 or 1200 kbps. I recently did a hookup over 200 feet but had to go down to 600 kbps.
If you have a vintage machine with no port but only a tape reader(ex. FANUC 5M OR 3000C and MITSUBISHI 5000CII) we install MEMEX products that can communicate at normal speeds and usually bi-directional for anywhere from $850.00 to $2000.00 . If memory capacity is a problem you can run most machines in tape mode but feed data "LIVE" from a pc
and then you can make programs as long as your pc hard drive run your machine. MEMEX makes FANUC upgrade boards for 6m, 10m, 11m and 15m and 16m, 18m controls also. We have used these at many shops but we recommend professional installation, as it is easy to damage circuit boards by improper wiring.
D -DISPLAYS all machines have some sort of a display for position , editing, alarms etc. Most use a CRT monitor and new ones use flat panel displays similiar to laptops. These have backlighting which is usually the first thing to go. However these are far superior to regular monochrome green displays. Almost all of the displays can be repaired if the actual
tube is still good. We have used many vendors to perform service on color crt's since they are expensive (around $2000.00). The older machines may have 7 segment type displays which are cheap , long lasting, but not user friendly.
Another type is GAS PLASMA displays. These die slowly, and fade out as they go. The Vintage MITSUBISHI 5000C and 5000CII controls use an obsolete version of this screen type that cannot be repaired. Mitsubishi no longer makes or supplies them but we can still have a few in stock for $2500.00 each. If you reach us through this site PLEASE let us know!
If a screen suddenly dies it is wise to check the power supply since this is usually easily and cheaply replaced or repaired. WE have 4 NEW Okaya Electric displays for the 5000 C-2 and that will be all. The company will not make any more.
ALL DISPLAYS WILL BENEFIT FROM A GOOD CLEANING FROM THE INSIDE OF THE SCREEN COVER AND THE ACTUAL CRT PANEL ITSELF! You'll find that you may not need a screen at all once you do this !
E- Electrical systems. This is a huge area to cover. Lets start with safety. Most machines have incoming 3 PHASE 208 VOLTS TO 480 VOLTS POWER! THE INTERNAL SERVO MOTOR POWER SUPPLIES CAN HAVE ANYWHERE FROM 300 TO 600 VOLTS DC. THERE CAN ALSO BE 480VAC INSIDE A MACHINE THAT IS SUPPLIED WITH ONLY 208VAC!
THIS IS LIKE TOUCHING A THIRD RAIL ON THE RR! THIS IS ENOUGH TO KILL OR SEVERELY SHOCK AND BURN A HUMAN! So remember to be VERY CAREFUL ONCE YOU OPEN THE DOORS. AND BE SURE NOT TO TOUCH THE DC POWER BUS FOR AT LEAST 15 MINUTES
AFTER COMPLETE POWER DOWN.(CAPACITOR DISCHARGE) ALWAYS CONFIRM IT WITH YOUR VOLTMETER!!! NEWER UNITS HAVE LED'S TO INDICATE CHARGES BUT STILL VERIFY IT! Now that that's said, there are some basic do's and dont's. Never connect anything that is not clearly marked and does not appear likely to have fallen off somewhere.
Check your wiring diagram or call the manufacturer. It may never have been attached and could cause serious damage. Most wiring has a connector number or wire number on it. On most newer Japanese equipment, for example DC wiring is done in blue .
But there are always exceptions. CHECK THE WIRING DIAGRAM! If fuses are blowing repeatedly something is wrong, either a short or an overload. NEVER , not even temporarily, use a larger fuse. You will surely burn out the circuit or even start a fire. And if a machine keeps tripping the main breaker or the one in the panel, LEAVE IT OFF until someone trained can check it.
Repeatedly powering up a failing or shorted drive can cause transistors to violently explode or cause a fire and burn up the amp, or worse, the entire control cabinet!!!
If the fuse is on a spindle drive or axis drive chances are that it is a SEMICONDUCTOR FUSE! This is a special type costing about $25 - $35 each. But don't be tempted to replace with a cheap fuse or you'll risk blowing the power transistors, capacitors or SCR 's (silicon controlled rectifiers)
in that unit. This can cost several THOUSAND to repair!!! And don't try soldering on a multi layer or surface mount board. It is almost impossible with conventional tools and you can render the circuit board unrepairable!
Check the circuit involved for obvious defects. Look at areas where wires bend or rub when the machine moves. Fixed(stationary) wires almost never break. Unless the wire duct or box is full of coolant. Then you must find the source of the leak and fix it AND DEHYDRATE ALL WIRES!
NEVER increase the allowable heat range on a thermal overload. Its there to stop the motor from overheating. You would never drain your radiator because it kept boiling over and drive the car for a few hours would you? Turning up the overload is like saying
goodbye motor! AND NEVER ! NEVER ! "TEST SWAP" ANY DRIVE BOARD THAT IS GETTING AN OVERCURRENT OR OVERVOLTAGE ALARM. IF THE BASE TRANSISTORS OR SCR'S ARE SHORTED YOU COULD DAMAGE ANOTHER BOARDS DRIVING CIRCUITS!!!( EX. FANUC OVC, OV OR DC ALARMS)
NEVER attempt tp disassemble a Fanuc, Mitsubishi, Gettys, Inland or Yasnac or for that matter almost any spindle or axis servo motor especially the permanent magnet type. If the magnet is not handled properly you will wipe out the magnetic field and dramatically
affect the motor's capabilities . You could damage the windings also. AC motors need no internal maintenance unless bearings wear out or coolant gets in. On DC motors the only maintenance you should
attempt is cleaning or replacing the brushes and cleaning the commutator. Only take out the brushes and use dry compressed air to blow out carbon. The feedback device can be replaced as a separate unit in most cases, just look for tiny set screws on the couplings and mark EXACTLY how it came off mechanically and electrically.
Also when an axis "RUNS AWAY" be sure to check encoder or resolver orientation AND correct wiring. Shorted feedback wires, improper grounding, dirty connectors, etc. can cause a litany of problems. You usually can swap them from another axis for test purposes, this may alter your home position a little, but this can be adjusted by parameters if needed.
You can also check the resistance to ground of any AC or DC motor with a meter range in megaohm range. Ultimately you should use a megaohm tester (megger) that will put out about 500 volts to look for ground faults. MAKE SURE THE MOTOR IS COMPLETELY DISCONNECTED FROM ALL SERVO DRIVE WIRING OR IT WILL DESTROY THE ELECTRONICS!!!
A reliable motor shop can do this test and rewind the motor and replace the commutator(dc) if needed. If you don't have a local shop either send it to the mfg.(FANUC has their own shop
and Mitsubishi uses an outside co. ) SEE THE SERVOS AND DRIVES section below for more information regarding that subject!
All actions on machine tools that involve a mechanical movement have to have an electrical confirmation that the action was completed. For an axis there is electrical feedback thru an encoder or resolver/tachogenerator and/or scales such as inductosyn or glass
All are subject to contamination by metal chips and coolant. Spindle motors also have a feedback device such as a tach or plg(pilot generator) which confirms the speed of the unit. If the speeds are erratic this is the first place to look. And there are limit switches
proximity switches, reed switches,pressure switches level sensors, etc that all can be checked in a program known to the CNC as the ladder.
If any one of these sensors is momentarily cut off or out of sequence it will either temporarily or permanently stop operation of the machine. Never push switches by hand. If the unit was not reset the motion could suddenly continue or reverse itself
CAUSING SEVERE AND LIFE THREATENING INJURY if a body part were to get caught in a mechanism. Always make sure to reset or put the machine into EMERGENCY STOP mode before trying to fix the problem. Never adjust a switch more than about .010 at a time and test
the unit carefully(limit or proximity switches). NEEDLESS TO SAY NEVER OPERATE A MACHINE WITH THE EMERGENCY STOP "HOT WIRED" ! You wont be able to stop the machine if something should happen and any stroke limits are likely to be bypassed also!
ALSO BE VERY CAREFUL WITH HYDRAULIC OR AIR SOLENOIDS. IF ANY DEVICES SUCH AS TOOL CHANGER GET STUCK IT IS TEMPTING TO PUSH A SOLENOID. DON'T DO IT UNLESS YOU ARE 100% SURE OF THE CONSEQUENCES! Some machines will wait minutes or hours for a limit switch to close.
If pushing a solenoid manually completes a sequence it may trigger several more events related to the function. Make sure not to push the wrong solenoid (out of sequence or not related to the function causing the problem) or you could soon find yourself with major damage or even injury.
Never push a solenoid or contactor with anyone else on or near the machine! Most solenoid operate with 110 volts ac or rectified ac. So you can get a shock if wiring is poor or damaged or if you are in a wet area. Don't unplug or remove a live solenoid.
L LEVELING and Installation It is of utmost importance that all equipment be accurately leveled and on a solid foundation. Never install machines where sunlight will shine directly on the casting! Keep it away from extreme temperature changes such as loading docks or garage doors. Use your manufacturers guidelines, or at least the minimum standards of no less than 1 foot of reinforced concrete rated at 3000psi or better for a machine weighing 15,000 lbs. For a 30,000 lb machine, about 2 ft of reinforced concrete.
You will always hear stories of some guy who placed his machine on only 3 inches of unreinforced concrete, but it will never maintain level and will eventually crack the floor. If a machine is leveled properly, it also should be anchored especially if it has fast rapids or weighs over 20,000lbs. The level must be checked over the range of motion of the machine.
For example,on a vertical machine, center the x axis and place a level parallel to the X axis on a very clean table in the center of both X and Y direction. Once you are "Rough leveled" you must move the Y axis to the front and rear of it's stroke. The level must not move more than one half of a division on a .001/per foot level. The goal is no movement! If it does, raise or lower the appropriate leveling pads.
You should be working primarily on only the 4 corner pads at this point, leave the middle pads off until the 4 corners are good. Then set up an indicator in the spindle with a bar enabling you to "Sweep" a circle of at least 2/3 of the Y axis dimension of the table ( the wider the more accurate you will be). You will find that your machine may be out .002-.004 inch at this point. Raise tha middle pads on both sides of the machine an equal amount,
maintaining the x axis level. Re- sweep the table, repeat this until you see less than .0005 inch or better. Also make sure you don't lift the machine off the rear or front pads. If you do and it is still not a good reading, you may have to anchor the machine to the floor. Re check the X level moving along the y axis. It should be within less than 1/2 of a division. If you find the machine slightly high or low in the static Y axis direction(level facing parallel y,
it is OK to be off a division or 2 as long as it is even. Recheck that all pads are touching. Most large machines, especially horizontals require expert installation, for more info please contact us.
M MACROS on most machines there is the capability to create specialized programs known as macros, which contain variables and can be used to cut special shapes, performing trigonometry or algabraic functions internally, and processing this data seamlessly while positioning the machine. It can drive sensors such as probes and tool length measuring devices. It also can be used to control tool changers, pallet changers, part loaders and some robot functions.
Most robots, however, use a "teach" mode to program the positioning of the device, but macro is used in the integration to the machine tool, along with a "macro interrupt" function. To debug a macro, make sure that the machine parameters are set so that "macro single block" is in effect, or you will not see which block contains the error. It may run a little slower but all math statements normally are processed in one shot, so 20 blocks may execute at once, even with single block switch on, if this parameter is not set first.
With line by line processing you can easily flag the error block when it actually occurs. Once you debug the macro, set the parameter back off and then the operation will be at least 40 percent faster. Drill cycles cannot be edited on fanuc controls but may be changed on almost all Mitsubishi models, we recently created a "peck tap cycle" on a 500 series Mitsubishi.
S- SERVO DRIVES INCLUDING SPINDLES WARNING THESE DEVICES OPERATE ON HIGH VOLTAGE. NEVER HANDLE THEM UNTIL THEY HAVE BEEN DE-ENERGIZED FOR AT LEAST 10 MINUTES. WHEN IN DOUBT CHECK WITH A VOLTMETER!!!
There are many types of drives in use on CNC machines. The first thing to determine when having problems is to see if they are AC or DC drives. If you are getting overcurrent or overload alarms it may be caused by the motor or the drive. You should physically inspect the motors and connection wiring first. The motor should turn freely by hand. Any noise may indicate a bearing problem. These usually must be replaced by a motor rebuilder. A DC motor will have brushes. They will be held in place by small plastic caps, usualy threaded into
the outer housing near the end of the motor. Many problems can be traced to dirty or worn out brushes. Turn off the power and wait 10 minutes. Then remove the brushes and inspect them. Re-install them in the same direction and position if possible. Blow out the motor with dry clean compressed air before
reinstalling the brushes and inspect the commutator ( the rotating surface that the brushes contact). If it is dirty try to clean it. If it has grooves, it will need to be repaired by a professional motor repair facility, which can also inspect the windings and rewind the motor if needed.
AN AC motor does not have brushes, and it is not a true AC motor. The AC is generated from a DC power supply and converted into a square wave AC with the negative portion of the wave clipped off. So these motors should last longer with no maintenance. For AC OR DC motors you should also check the resistance to the motor frame in the mega-ohm range, if it is below the mfg reading it means the winding insulation has deteriorated and must be repaired or replaced. ANY signs
of moisture or coolant inside the motor usually means rebuilding or replacement of the motor is necessary and try to determine how the moisture originated and seal it off properly. If the moisture is inside the connector take it apart and clean it good, dry it with compressed air, and try to run the motor again. Sometimes the connector will need to be replaced.
If the motor checks out OK, see if the feedback units are working properly. These may be encoders, resolvers, pulse coders, inductosyn scales or glass scales (Heidenhain) or tachogenerators and PLG's (pilot generators) or a combination of these devices. A tachogenerator can only detect speed so it is used with spindles by itself, or on axis combined with scales. Encoders generally are the most common axis feedback device because the can detect speed and position.
If any of these units cause a problem it is usually going to cause an alarm and you can "SWAP" the offending unit with another axis and see if the problem moves. Be sure to mark the exact mounting position, or you home position will shift on the axis. For scales, they usually are a problem since dirt gets into them and are costly and difficult to replace. If you are lucky and the machine mfg. used regular encoders on the axis you can usually remove the scales and change
a few parameters and run the axis without the scale, it won't be as accurate, but it will work. Your pitch error and backlash will have to be updated if you choose to make this a permanent solution. If the problems remain, you then may swap the servo drive boards, but NOT if they have an overcurrent or discharge alarm! Doing so may damage another board. You can test for bad tranistors or thrysistors in an amp base and try replacing those components but there is frequently damage
to the driving board and you risk destroying the new component you installed if the driving circuitry is not repaired. Make sure they are identical and make sure you wait at least 10 minutes before even touching the servo drive amps. CHECK ALL JUMPER and ROTARY SWITCH SETTINGS BEFORE ENERGIZING. Also verify that all software on ROMS is compatible, when in doubt, swap the chips and be careful not to discharge any static on the components!
Spindles usually cannot be swapped unless you have more than one machine and the boards are an exact match. Always contact the control or machine manufacturer if there are any doubts. Do not attempt to replace board components yourself unless you have the soldering skills and schematics for the units. READ THE ELECTRICAL SYSTEMS section before proceeding!
S- SPINDLES AND BEARINGS. A major component of all mills and lathes is the spindle. It is the central point of wear and tear on a machine. Most lower speed spindles ( below 8000 or 10000 rpm) are permanently lubricated with a special grease such as KLUBER ISOFLEX NBU15 or similiar grease. The amount used is critical, too much is as
bad as too little. Always check with the machine mfg regarding the amount of grease, and ask if the bearings are already lubed. Otherwise use an approved solvent to was off any residual protective oils and then carefully put in the exact amount called for. Also it is HIGHLY RECOMMENDED to buy bearings from the machine mfg. for spindles since they often have been modified
specifically for the application and the bearing mfg. may not be aware of this. And do not attempt to rebuild anything over 6000 rpm without getting it balanced after reassembly. Follow the machine mfg. instructions on tightening up all components and follow proper break in procedures. You will have to appoint someone to observe the machine for load, noise and heating up during this phase or you could
destroy a new set of bearings costing from about 900 to 6000 dollars per set (new ceramic bearings are $5000 to $6000). If you have never done a spindle job before seriously consider turning it over to an expert! And if you have coolant injection thru the spindle make sure to remove the tool whenever the machine is going to sit overnight or longer and wipe out the taper or you will get rusting and deterioration. Also the less coolant aimed directly at the spindle minimizes chances of
contamination of the bearings which leads to premature failure
S-SUMMER IS COMING and it is time to check all of the cooling fans inside and out of your machine,including the ones hidden behind amplifiers and control circuits. Again most standard fans can be replaced by anyone but ones which are soldered to the rear of drive amps should be done by professionals. Also check all of the filters and spindle motor fans, spindle oil chillers and hydraulic radiators before the onset of heat. Make sure that all chillers are properly charged with refrigerant (FREON 12, 22 or 134A etc.)
If you have not changed your oils now is a good time to do it. Check your way lube system completely and grease all fittings and counterweight chains if any. And give your machine that long overdue cleaning! It will appreciate it!, and so will your service person!
This site is for informational purposes only and does not recommend anyone taking any of the actions within this page
© Denis Byrne and Global Machine Dynamics