Category Archives: Linear Motion Design Considerations

Aerospace, Automotive, Chemical, Communications, Electronics, Factory Automation, Food & Beverage, Linear Motion Design Considerations, Medical, Military & Defense, MRO, Packaging, Steel, Transportation, Uncategorized

Industry Insights at Arm’s Reach

August 18, 2015 admin Leave a comment

With so many markets, products and changes happening within the industry, it can be a challenge for designers to know where to find reliable and helpful information . Luckily, we’ve provided two companies who work hard in delivering topnotch, insightful content to help broaden your knowledge of the industry.

You might know Rockwell Automation as the world’s largest company for industrial automation and information, but did you know the company delivers a wide array of white papers, tools and other industrial automation methods, trends and technologies? The Journal from Rockwell and Our PartnerNetwork™ recently published “The Basics of Ball Screws,” which teaches the key terms, preloading methods and calculations for understanding ball screws.

Rockwell also provides beneficial tools, such as its “Motion Analyzer,” which offers an inertia calculator and compatibility browser for a variety of different products, including linear motion products & systems.

Design World provides daily news in the industry, videos, tech tutorials, webinars and trending topics.According to its website, “Design World is written for engineers by engineers with an emphasis on applying the engineering fundamentals to real world machine design applications across industries including medical, packaging, semiconductor, material handling, and off-highway.” From pneumatics to robotics, the magazine and its digital brand stand as invaluable resources for designers and engineers who wish to be ahead of the curve in the latest industry happenings.

Aerospace, Automotive, Chemical, Communications, Electronics, Factory Automation, Food & Beverage, Industries, Linear Bearings and Pillow Blocks, Linear Motion Design Considerations, Linear Slide Systems, Medical, Military & Defense, MRO, Packaging, Paper, Steel, Transportation

Getting the Most out of Your Linear Bearings (Part 2)

August 11, 2015 admin Leave a comment

In order to get the best performance and life out of your linear bearings, proper lubrication is key.

A lubricant formulated for rolling friction should be used with linear bearings. In applications where operating speeds are low and loads are light, linear bearings can be used without lubrication at a greatly reduced life. However, it is never recommended to operate linear bearings without lubrication. To protect the highly polished bearing surfaces from corrosion and wear, a lubricant is required.

Where linear speeds are high, a light oil should be used and provision for re-lubrication should be made to avoid operating the bearings dry. For typical applications, a medium-to- heavy oil has good surface adhesion and affords greater bearing protection. Linear bearings 2 inches in diameter and above may use high pressure lithium grease such as Shell Alvania #2 for moderate speed applications. Lubricants containing additives such as molydisulfide or graphite should not be used.

Aerospace, Automotive, Chemical, Communications, Electronics, Factory Automation, Food & Beverage, Linear Bearings and Pillow Blocks, Linear Motion Design Considerations, Linear Shafting and Shaft Supports, Linear Slide Systems, Medical, Military & Defense, MRO, Packaging, Paper, Steel, Transportation

Getting the Best out of Your Linear Round Rail Bearings (Part 1)

August 6, 2015 admin Leave a comment

In order to get the most life and best applications out of your bearings, it’s important to understand the size of the load, how the load will be applied and the length of the stroke. Applying too much weight to a load can significantly reduce the life and efficiency of your bearings. Also, incorrectly distributing the weight on the load can be harmful. In addition to some helpful design considerations, let’s take a look at the load considerations below.

Load ratings are the required design life, shaft hardness and bearing dynamic that affect the load and can be applied to a linear bearing. Two dynamic load ratings are given for each bearing size based on the rotational orientation of the bearing.

The normal load rating is used in applications where the orientation of the ball tracks relative to the load cannot be controlled. The normal load rating is based on a load imposed directly over a single ball track. The normal load rating shown in the specification tables is slightly greater than would be mathematically calculated based on one track loading, because it assumes that the load is shared to some degree by one or more of the adjacent ball tracks.

The maximum load rating assumes that the load is applied midway between two ball tracks as illustrated below. In this orientation the load is distributed over the maximum number of bearing balls.

The normal and maximum load ratings are based on a Rc 60 shaft hardness and a travel life of two million inches. For linear bearing system operating at less than full rated load, the Load-Life Curve may be used to determine the travel life expectancy.

An equivalent load value can be calculated when sizing linear bearings for applications at conditions other than maximum rating.

Acme and Lead Screw Products, Ball Screw Jacks, Ball Screw Products, Linear Motion Design Considerations, Planetary Roller Screw Products, Screw Accessories, Screw Jacks, Worm Gear Ball Screw Jacks, Worm Gear Machine Screw Jacks

Three Popular Screw Types Defined

July 29, 2015 admin Leave a comment

When considering the vast majority of applications in which machine screws are used, it’s important to review the functions of some of the major types of screws. Below, we’ll take a look at the designs, functions and more while we define acme, ball and planetary screws.

Acme Screws:

The acme screw thread, sometimes referred to as the trapezoidal thread, is used for lead screws. They are often needed for large loads, or when the environment is less than desirable.

The acme thread form has been around for over a century, replacing square thread screws which had straight-sided flanks and were difficult to manufacture.

There are two main classes of acme thread forms: general purpose (G) and centralizing (C). The general purpose and centralizing thread forms have a nominal depth of thread of 0.50 x pitch and have a 29 degree included thread angle, which has allowed companies to develop unique screw diameters and leads. European metric Trapezoidal thread forms have a 30 degree Included thread angle.

When compared to general-purpose thread forms, centralizing threads are manufactured with tighter tolerances and reduced clearance on the major diameter. For instance; If an acme nut is side loaded with a radial load, a “G” class will wedge when the nut thread flanks come in contact with the screw thread flanks. To prevent this wedging, a “C” class thread form can be used, since it utilizes less clearance and tighter tolerances are allowed between the major diameter of the nut and the major diameter of the screw.

Industry leaders have developed several unique thread forms, such as stub acme forms and 40 degree included angle, which allow them to provide a variety of diameter and lead combinations.

Ball Screws:

For loads requiring a greater amount of efficiency, companies often turn to ball screws. A ball screw assembly is a device comprised of a nut, screw, and reciprocating ball bearings. The bearings provide the thread engagement between the nut and screw.

Ball screws offer an efficient means for converting rotary motion to linear motion. A ball screw is an improvement over an acme screw just as an anti-friction ball bearing is an improvement over a plain bushing.

In the long run, ball screw systems can prove to be a cost-effective alternative to pneumatic or hydraulic systems, which require constant electrical and air power.

Planetary Roller Screws:

Planetary roller screws are remarkable devices designed to convert rotary motion into axial force or vice versa.

The planetary roller screw design offers multiple advantages and reliability for the most demanding applications when compared with other lead screw types due to its rolling motion. These screws offer high efficiency even in relatively shallow lead designs.

The multitude of contact points can carry large loads and provide very high resolution (small axial movement) when using very shallow leads. Planetary roller screws produce high rotational speeds with faster acceleration without adverse effects.

Ball Screw Products, Linear Motion Design Considerations

Ball Screws: The Basics

July 7, 2015 admin Leave a comment

Of all the screws in industry used for motion, ball screws provide unique benefits when compared to other standards, such as roller screws or acme screws. A ball screw is a device comprised of a shaft and a nut where either of which can be the traversing component.

Ball screws work similarly to ball bearings, where hardened steel balls move along an inclined-hardened inner and outer race. With at least 90 percent efficiency, ball screws are one of the most efficient ways of converting rotary motion into precision linear motion. When it comes to ball screws, there is some key terminology to understand.

The ball circle diameter is the diameter of the circle created by the center of the ball bearings when they come into contact with both the screw and nut. The root diameter is the minimum diameter of the screw measured at the bottommost point of the threads. Both diameters are important when calculating application characteristics and sizing parameters for factors such as column loading and critical speed.

Pitch is the axial distance between two consecutive threads on a screw. Lead is the linear distance traveled by the nut or screw when either is rotated during one full rotation. The starts are the number of independent threads on the screw shaft. There are typically one, two or four starts on a screw, which resemble a helix that wraps around the shaft. The pitch multiplied by the number of starts equals the lead of the screw.

Lash is the result of the axial movement between a nut and screw without rotation. While lash can disrupt the accuracy of the screw, it is typically an occurrence that comes without any serious issues. Normal screws come with a relative amount of lash, and screws which are only loaded in one direction won’t be affected by lash. Lash can be controlled through processes called preloading.

Preloading is the result of an internal force introduced between a ball nut and screw assembly that eliminates free axial and radial lash. There are three methods used for preloading. The double nut method uses two ball nuts that are loaded in opposing directions by a spacer, so that they don’t wiggle when stationary. Lead shifting is a method where a shift or offset is manufactured in the lead of the ball nut. For example, a lead might be shifted from 5 millimeters to 5.05 millimeters in order to shift the ball bearings inside the ball nut in a different direction. This is the preferred method when considering compactness, but load capacity will be reduced. Ball selection is a low-cost method that involves using oversized ball bearings to create four points of contact between the nut and screw. This allows for a heavier load, but the friction from the contact can reduce the life of the bearings.

Making Motion Work