Steinmeyer recently added a key individual to its USA sales force. He is Bruce Gretz. Bruce has 30 years’ experience in various high tech businesses including Loral and Rockwell. Most recently he was Sales Director for PremaTech Advanced Ceramics. He holds degrees in Mechanical Engineering (BS), Aerospace Engineering (MS), as well as a MBA. Bruce is located in Massachusetts, at the Steinmeyer Inc. office in Burlington. He can be reached at (781) 273-6220 and/or email@example.com.
Steinmeyer recently added Custom Precision Solutions (CPS) as our representative for the southeast USA. Dominic Mastroianni, president of CPS, is located in Wake Forest North Carolina and covers the following states: Maryland, Virginia, North Carolina, South Carolina, Tennessee, Georgia, Alabama and Florida. Dominic has 20+ years’ experience in motion control and represents a wide variety of premier manufacturers including Precipart, Autotronics and BEI Sensors. For Steinmeyer he will concentrate on ground ball screws and focus on applications in commercial aerospace and robotics markets. Custom applications are especially relevant since he represents so many items designed to function together. With more and more engineering designs being outsourced, it is especially important to rely on experienced engineers that know how to choose and integrate the right elements that comprise a precision motion system. Dominic can be reached at (919) 868-3628 or via email at firstname.lastname@example.org.
Seems there is still a lot of confusion on load and life ratings when it comes to ball screws. Many people are familiar with the classic L10 life equation L10 = (Ca/P)^3 x 10^6 revolutions where Ca is the dynamic capacity in N and P is the mean applied axial load in N. Recently we fielded several inquiries on applications where an engineer wanted to know whether s/he can apply a force equal to Ca and achieve 1 million revolutions of life. Or even higher than Ca and achieve less than 1 million revolutions. The basic answer is NO! Here is why:
Most industrial ball screws are designed for a Ca/P ratio greater than 3. In many machine tool applications, the Ca/P ratio is actually as high as 10, bringing the calculated life expectancy close to 10^9 revolutions. That is the load range for which most industrial ballscrews are designed, and for which the life equation has been proven in thousands of applications. There are other effects that limit life (such as micro-welding and/or abrasion which cause loss of preload over time) but these are not factored into the classic life equation, and come into play mainly at the high end of the life calculation, that is beyond 1 billion revolutions. A ball screw that failed after 20,000 or 30,000 hours is typically not going to cause many questions to be asked as to what the reason was. So, for practical reasons, don’t rely on calculated life expectancies beyond 10^9 revolutions unless everything, including lubrication and protection from contamination, has been reviewed carefully.
If the load is higher than one-third of the dynamic load capacity, the contact forces between balls and races might become greater than was anticipated in the design of the ball screw. This could lead to accelerated wear, reduced smoothness and premature failure in general. In other words, the life equation is no longer valid in this range.
So, in our experience, the reliable scope of the equation is between 30 million and 1 billion revolutions. This means the allowable applied load is between about 10 and 30% of Ca – again, this is for most industrial ball screws.
It is possible to design a ball screw for operation outside this range – we do it all the time. But certain design parameters of the ball screw must be adapted to such usage. Lubrication can also get tricky at either end of the load range. For example, some frequently used lubricants may not be able to handle the contact pressures of a ball screw operated at or near its dynamic load capacity. Best to contact a ball screw engineer to review it.
Often customers are a little surprised when they embark on the Geometric Dimensioning and Tolerancing (GD&T) phase of their design asking – “why must I design in such tight alignments, concentricity and squareness?” The answer is simple… so the ball screw will operate at its fullest efficiency and anticipated life! Continue reading
Seems like everyone’s pushing the limit on ball screw speed lately. Steinmeyer introduced our UltraSpeed ball screw series several years ago, boasting of Dn values to 160,000. First, what’ s Dn value and what does it signify? Continue reading
Or to put it another way – the old adage was “if you want a really smooth ball screw with zero backlash you have to specify and pay for a ball screw with higher accuracy”. But is this true today? The short answer is a decided “NO!” Years ago, even ball screw manufacturers believed that a more accurate ball screw, e.g. grade 3 or grade 1, was inherently smoother than a grade 5 (for a clearer definition of what the grades actually mean, please go to our web site):
At least once a week we get such an inquiry – someone looking for a ball nut and separate shaft long enough so they can cut it and machine the journals themselves, usually thinking this will significantly reduce lead time. And of course, compared to buying a completely custom ball screw, it may just do that. There are several reasons why we do not offer separate shafts and ball nuts, or complete ball screw assemblies with unfinished ends. Continue reading