About this Blog

This blog is written by engineers for engineers.  It is meant for anyone wanting to expand his/her knowledge of precision ball screws, especially regarding the Steinmeyer product line.  We will post a variety of subjects regarding product design and selection, give advice to machine designers, and answer general questions about ball screws.

The editors of this blog are professionals with decades of experience in the motion control industry.  They are knowledgeable about ball screw applications in machine tools, aerospace, precision instruments, and general mechatronics. We will do our best to provide the most accurate and useful information possible.*

We welcome your participation and feedback!

* There is no guarantee that the information provided in this blog is correct and sufficient for the proper and safe operation of ball screws and related products, and thus the editors and contributors to this blog cannot be held liable.
Photos and logos are used with permission from Steinmeyer GmbH & Co. KG, Albstadt, Germany.

2 comments

  1. frankjconway

    I’m sizing a motor/ballscrew system and am having trouble understanding the “maximum friction torque” you have listed in your literature. Sizing calculations use different terminology in the equations. This value is becoming the dominant torque in my calculations….more so than I would have suspected. Could you explain what the “max friction torque refers to, exactly? Is it the same as breakaway torque? Thank you.

    • ballscrwblog

      Hi Frank,
      Friction torque of a ballscrew is driven by two things:
      1) preload: “oversized” balls are compressed between nut and shaft. This part of the friction torque reacts heavily to machining tolerances. The slightest increase in thread diameter of a certain portion of the screw shaft causes a substantial increase of the preload, which in turn causes additional friction.
      2) viscous friction: Balls are plowing through the grease or whatever lubricant is used. This portion of the friction goes up in lower temperatures, or if fresh grease is applied. Wipers also add to this.
      All in all you could say that the upper torque limit is typically very generous and reflects an addition of all thinkable worst cases.
      You have however the possibility to specify an upper limit torque. Only don’t request things like “high stiffness (meaning considerable preload), but no torque”. But if you request a maximum upper torque limit of 50% of the published value, that might still work without sacrificing much else (it might cost some money though). And if your application is torque sensitive, you may want to think about specifying a less viscous lubricant (especially advisable if speeds are high!), get rid of the wipers if you work in a clean environment, or ask for reduced preload.
      BTW, “breakaway torque” of a ball screw is typically lower than “running torque”. The reason is that some (or most) of the friction is viscous.
      The torque needed to produce axial thrust is not included in this! If the ballscrew is pushing hard, then this torque becomes dominant.

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