Ball Screw Repair FAQs

I have started having trouble holding size on my machining center, especially when using circular interpolation. The ball screws seem to be running quietly and there are no strange noises when the slides move. Do I need to have the ball screws reconditioned or is it a problem with the control?

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It could be a problem with the control but it is more likely to be mechanical.
First, measure the part to try and determine which axis is mis-positioning. If it is both, proceed one axis at a time using the following steps. Determine if the encoder (pulse generator) is connected directly to the ball screw or attached to the servo motor. If the encoder mounted motor is connected directly to the ball screw with a coupling or the encoder is mounted to the end of the screw, check for movement in the ball screw thrust bearings with an indicator on the end of the screw. If an encoder mounted servo motor has a belt or gear drive to the screw, the adjustment could be incorrect. If these checks fail to account for the tolerance error it is likely there is backlash in the ball screw.
It is possible, with the servo disconnected, and if the backlash is more than 0.001 inch, for movement to be felt using a light touch.
There could also be a problem with the spindle bearings, if the metal being removed is not uniform, as with a casting.

I just bought a turning center at auction and there appears to be a problem with both the “x” and “z” axis ball screws. They are noisy and there seems to be excessive backlash in both. Can they be reconditioned?

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In most cases yes, but because turning centers are prone to catastrophic collisions with a revolving chuck, occasionally they are damaged beyond repair. It will cost nothing to send the ball screw for a free evaluation. Most ball screw rebuilding companies offer this service and you could save money.

How can I be sure that the backlash shown on the control’s readout is in the ball screws?

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With the machine assembled you can never be absolutely sure but there are ways to improve on sheer guesswork. The encoder (a rotary pulse generator) or a linear scale (a linear pulse generator) feeds signals to the control. A linear scale is mounted directly to the slide and way so bypasses errors in the ball screw and thrust bearings. An encoder relies on the accuracy of the ball screw and thrust bearings so control manufacturers invariably incorporate an electronic backlash elimination to alleviate any problems. Over compensated electronic backlash elimination can often cause jumping when slide direction changes.

When I move the “y” axis slide on my machining center close to the limit the servo motor trips out. Is it likely to be the ball screw or the servo?

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It is unlikely to be in the servo motor drive.
“y” axis slides on many machining centers are equipped with heavy sliding way covers that often get damaged by falling parts and tooling or just clogged with chips. When the slide moves toward it’s limit the load on the servo motor exerted by the damaged cover can trip the motor.
Similar symptoms can be caused by an incorrectly installed ball screw.

We did some work on the table slide of an older boring mill but two weeks later the ball screw locked up. One wiper was pushed out and pieces of ball could be seen in the end of the nut. A week after we installed a new ball screw the same thing happened. What is the problem?

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Each ball screw is design to operate up to a predetermined load. When the load on the unit is excessive the ball screw fails, your case is a prime example of this. The chances are that either the slide is too tight, the ball screw is incorrectly installed, or both. This type of problem is quite common when machine tools undergo major rebuilding because slide-ways are reground and turkite replaced changing the relative position between slide and way.

I clean the ball screw on my machine regularly but the seals on the nut allow small particles to enter. The seals seem to be made of some sort of plastic. Can I replace them to keep the chips out?

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The seals you mention are in fact wipers because it would be almost impossible to perfectly seal a ball nut. Manufacturers use varying materials to accomplish the task but the results are rarely 100% efficient. Plastic, neoprene, felt and brush wipers are used, some ball screw designs are supplied without wipers. All have their advantages and disadvantages depending on conditions of use. In your case, continue to clean and lubricate the ball screw but do not use an air gun to blow away chips. The use of compressed air to remove chips from a ball screw should be avoided.

There is backlash in one of my ball screws but the screw itself looks to be in good condition. I was considering to try to replace the balls myself to keep the cost down. Would you recommend it?

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Working on a ball screw is not rocket science and anyone with reasonable mechanical abilities should be able to perform the task. It’s a little like working on your own car, there are some jobs you know you have the ability to perform and others you leave to the professional. The problem with do-it-yourself ball screw repair is if you make a mistake it can damage the unit beyond repair, and that can be expensive. In the final analysis it’s a judgment call you have to make for yourself.

I put a new ball screw in the table slide of my machining center but I still have backlash. Why is that?

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Most likely the ball screw thrust bearings were not replaced or installed correctly, or the servo motor drive mechanism is not adjusted correctly.
Many machine tool manufacturers use a servo motor with a toothed timing belt to drive the ball screw, it is important that this belt is adjusted correctly so that it doesn’t cause errors in positioning.
Also, if the electronic backlash elimination built into the control has been changed, it may need to be reset for the new screw. To do this it is best to make note of the existing setting then start from zero and gradually increase the parameter settings until the best result is achieved.

I have a laser cutter with a ball screw that is approximately 1.250 inch diameter and 12 foot long. It is time for me to have the unit reconditioned and I was thinking of taking it out of the machine and reinstalling it myself. Is there any special way to approach this and are there pitfalls to be avoided?

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Long, small diameter ball screws are notoriously difficult to install correctly. Contrary to common belief, ball screws are not perfectly straight and long screws are the worst offenders. To work around this problem it is necessary to install the unit in a predetermined order. If the thrust and support brackets are left in position (this may not always be possible) when the ball screw is removed from the machine, it makes the task a little easier.
When installing the reconditioned ball screw, first assemble in the thrust and support brackets and make all final adjustments to the bearings. With the ball nut all the way to the end that will allow for tightening of the securing bolts, move the slide until it comes gently into contact with ball nut flange face. Snug the bolts down alternately until the flange is locked down. It is important to move the slide it’s full travel, turning the ball screw by hand and noting any perceived tightness. Only when it is confirmed that the ball screw is installed correctly should the servo motor be attached.

I had a new ball screw installed in my machine two years ago and although it is positioning OK it is starting to make a noise again. How long should a ball screw last in a turning center?

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It is not unusual for a ball screw to still be functioning efficiently after 20 years of continuous use. If a high quality precision ball screw is well maintained, is supplied with adequate lubricant of a suitable grade and doesn’t suffer mis-treatment, then it should outlive the life of the machine it is in. The problem is that very few ball screws avoid the vigor’s of abuse, tight production schedules and poor maintenance, that is why Express Ball Screw Repair is in business.
Aside from machines operating in extremely contaminated conditions, the turning center is probably the worst culprit for destroying ball screws. Some of the more powerful machines in the 10-12 inch chuck range sport 50 and 60 horse power spindle motors that when turning at top spindle rpm store an enormous amount of kinetic energy. When this energy is suddenly released as happens when a tool rapids into the chuck, it is not difficult to appreciate the damage that can be caused to a machines components. This is why an otherwise premium quality ballscrew is likely to have a shortened life in a turning center.

A ball screw in one of my machines locked up and on inspection some of the balls have split in two pieces. Why did this happen?

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When balls are split in two pieces like peas it is invariably caused by extreme pressure. Usually this pressure is the result of a mis-aligned ball nut. It is important when installing a precision ball screw to ensure that the ball nut flange face mates perfectly with the contact face of the nut housing or a lateral twisting can occur causing extreme pressure inside the ball nut. It is possible, especially on nut housings that are bolted and pinned in position, that alignment of the flange contact face was changed because of a collision.

I want to adjust the gibs for the slides on one of my machines. How will I know if the slide is adjusted correctly? Will I have to disconnect the ball screw and servo motor and push the slide or can I do it assembled?

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It is not necessary to disconnect the ball screw and servo motor to adjust the gibs of a slide but some precautions should be taken before the task is attempted. Usually the reason a slide needs adjustment is because it is worn. Unfortunately, slides rarely wear evenly which limits the effect of adjustment. With the ball screw and servo attached to the slide it makes it difficult to “feel” the slide’s tightness so it is necessary to employ the use of a torque wrench to replace the “feel.” Before adjusting the slide, measure the torque required to turn the ballscrew at various places along it’s travel. Then slowly adjust the gibs, one at a time until each starts to increase the torque. Bear in mind that the ends of the slide’s travel will be worn the least. Also, adjusting the gibs theoretically changes the position of the center line of the ballscrew.

The turkite has started to come unglued on a machine I am trying to rebuild. I am considering replacing it and wonder if doing so would cause problems when the ball screw is reinstalled. I know the ball screw should to be aligned accurately but just how precise does it need to be?

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It depends on many factors but assuming it is a high precision machine with a quality ball screw the alignment needs to be commensurate with the accuracy of the machine. Ideally alignment in all plains should be 0.001 inch or better but on some older machines it may prove impossible to achieve. It has been said that the single most critical alignment for a ball screw is the ball nut contact flange mating surface. You can always double check for tightness with a good quality dial type torque wrench.

What exactly is a preload when associated with a bearing or ball screw and how can I tell if the preload is correct?

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This is a difficult question to answer because a preload becomes increasingly difficult to measure accurately after it passes zero preload when the variables become almost unmanageable. To give insight into these variables lets consider a simple precision roller bearing preloaded at the factory. It is then pressed into a tool bored housing and onto a ground shaft, each with an upper and lower tolerance. The shaft is then spun which causes friction between the preloaded surfaces, which induces heat and expansion, which again increases the preload even more. During a period of running, wear occurs decreasing the preload. Now what preload do you have?
There are ways to ensure that a preloaded device stays within efficient limits but many of the variables must be known.
In the case of a ball screw, consider that when the servo motor spins the ballscrew from stationary to 1000 rpm it requires the preloaded balls to instantly absorb the load exerted by the mass of the slide. But it is only the balls in the tracks responsible for taking the load in that direction that are affected. The balls in the opposite track momentarily become non-loaded. So what preload do you have on them?
To preload a device to perform flawlessly is like playing the violin, some can do it but most can’t, and for those that can, it takes constant practice to play it well.

Turnaround

Standard: Within 7 days / Express: 48 hours

We understand how important it is for you to have your machines up and running. American Ball Screw Repair specialize in fast turnaround time and can have your machine back in full working order and making you money again in double quick time.

American Ball Screw Repair offer a number of different service speeds to fit the urgency requirements of our large client base.

Our Standard Service offers a turnaround time of 7 days.  It does exactly what it says on the tin. Your ball screw will be returned to you fully reconditioned within 7 days.

Our Express Service offers a turnaround time of 48 hours for clients who simply cannot afford 7 days downtime.  Rest assured that despite the incredible speed of our Express service the quality of your ball screw repair will be still be second to none and with no loss in accuracy.

American Ball Screw Repair even offer an Emergency Weekend Service as part of our Express Service whereby we receive your ball screw on Saturday morning and ship it back to you on Monday morning.

We always make sure our clients are fully aware of the cost and shipping dates associated with their chosen service before commencing any repairs.

Guarantee

1yearAmerican Ball Screw Repairs offer a full one-year guarantee on all our ball screw rebuilds and reconditioning services.

The exceptional quality of American Ball Screw Repair rebuilds means that often, particularly with some lesser quality ball screws, the rebuilt unit is often of better quality than the original manufacturer specifications.

We won’t carry out any work unless we think we can guarantee you a saving when compared to replacing your unit.  We also offer all our clients technical support if you experience any problems with your reconditioned ball screw after delivery.

Quality

Companies exist that produce an inferior product despite being ISO 9000 certified, and yet others with the finest measuring and testing equipment have problems with reliability because the workforce is not motivated or skilled enough to produce a good product.

We base our work ethic on experience and good old fashioned craftsmanship. Each precision rebuilt ball screw unit is not only measured for accuracy but also passes the “human” test – and a reconditioned ball screw is not shipped unless we are totally happy with it.

Our ball screws are rebuilt with super fine surface finishes and quality components for long life. They are individually preloaded to give the highest possible positioning accuracy. They look and perform as they did when new.

LEARN MORE ABOUT OUR QUALITY REPAIR PROCESS HERE

We do occasionally make mistakes but it is not in our interest to do reworks so it is paramount we get it right the first time. That is our promise to you.

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