Lubrication Challenges for Small Linear Motion

Like all motion control devices based on contact friction, ball screws require lubrication for proper functionality. The reason is that lubrication is required for smooth recirculation of the rolling elements. Even if a dry lubricant coating is applied to the ball screw elements (shaft, nut and balls), some small amount of conventional oil/grease is still required. In other words, the ball screw cannot properly operate while completely dry. All Steinmeyer ball screws are pre-lubricated at the factory – but only with an initial fill amount. For most applications, we recommend an initial lube check after 500 hours of machine time. Based on that inspection, adjust the maintenance schedule accordingly. Of course, every application is different, and users should develop their own maintenance schedule based on the particulars of their operation.
One common scenario that can cause lubrication challenges is repeated use of a small segment of the total working volume. For example, let’s say your X and Y axes have a total travel of 1 meter, but you are machining an area of the part only a few centimeters long. If your machine performs this task repeatedly on many parts, a large portion of the X and Y shafts will be exposed to the environment without ever being swept by the nuts. Plus the balls inside the nut will not receive fresh lubricant. As a result, they may lose lubricant while gaining buildup of dirt, dust, and swarf. These conditions increase the risk of excessive wear when the machine returns to other operations.
To guard against this scenario, we recommend two solutions. The first is to create a designated lube “station” at the opposite end of the small operating range. Move the nut to this “station”, apply lubricant, and then return. This operation will ensure the shafts are not only wiped of debris (presuming there are proper wipers at both ends of the ball nut) but also evenly lubricated. Alternatively, if shaft contamination is minimal, you may inject lubricant into the nut while still in the small operating range. Move the nut at least one length to distribute the lubricant evenly within the nut. When the machine returns to other operations, there will be sufficient lubricant inside the nut to cover the shafts properly. See the Steinmeyer web site for re-lubrication guidelines for both oil and grease – lubrication quantities vary based on shaft diameter and nut type.  Another alternate solution is to lubricate through the shaft – that is the shaft is cross drilled to allow lubricant to pass through it and into the ball nut at a designated location.  This is especially useful for certain oscillating motion situations.  For any further questions or suggestions please contact one of our application engineers!

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