Ball Screw Repair
Choosing between rebuilding or replacing ball screws can be a difficult decision to make. New ball screws may be the right choice based on price and availability, but it is usually wiser to have the screw reconditioned. This can save business money and downtime, as ordering a new ball screw can take weeks to assemble while a repair can take only a few days.
Quick links to Ball Screw Repair Information
How to Determine if a Ball Screw Needs Repair
Ball screw failure is often caused by gradual degradation of the screw surface or machine crashes that result in a bent screw. Visible damage or lack of functioning will alert you that the ball screw has a problem. Cracks, dents, or physical breaks are an indication that the ball screw is not in optimal condition. If the screw is worn out, the backlash will increase and efficiency will decrease, causing the screw to require extra torque or horsepower to turn. When the screw is worn out, the lead accuracy could be worse than required.
Measuring diametral backlash can determine if a ball screw needs repair. To do this, place the ball screw assembly in V blocks, then lift the ball nut vertically and, with a gauge, measure the play between the ball nut and the screw. Minimal, or Level 1, repair is needed to bring the screw back into use. A lash of 0.0035 in. represents 80% wear and indicates either a Level IV repair or a dead ball screw. Similarly, for non-preloaded assemblies, a diametral lash of 0.009 in. is 50% wear and needs Level 1, and 0.015 in. is 80% wear and needs Level IV or replacement.
Types of Ball Screw Repair
- Level 1
- Addresses the most common problems, such as loss of repeatability due to wear. Balls are the first to wear. During repairs, new, larger balls are used at every level to restore preload and repeatability.
- Level 2
- Involves regrinding of the ball nut to the steps taken in Level 1.
- Level 3
- Adds regrinding of the ball screw threads and, as required, rebuilding of the journal diameters with eutectic spraying and grinding them back to size.
- Level 4
- Adds regrinding of the ball nut and ball screw. This level is the most costly, but it can restore a damaged ball screw to a normal new screw lifespan.
Points to Consider When Considering Ball Screw Repair
When considering a repair service, it is important to make sure a servicer holds an adequate stock of supplies. Additionally, turnaround time and quality are important factors. Some repair services used refurbished balls, which can impact the overall life of a ballscrew. Others may not use a larger sized ball when making repairs. Using a larger sized ball allows for the screw to be restored to the level of preload and repeatability it once had.