What makes miniature ball screws unique?

Ball screws are used in a variety of applications,but some of the most challenging are at the extreme end of the performance spectrum-from large diameter,large lead screws for machine tools,to small diameter screws with extremely fine leads for optical and medical applications.For very small,high-precision movements,designers and engineers often turn to miniature ball screws.

While there is no industry standard that classifies screws as "miniature,"most manufacturers apply the name to screws less than 16 mm in diameter,while others include 16 mm screws in their "micro" product lines.To further subdivide the size range,screws less than 6 mm in diameter are sometimes referred to as "sub-miniature" or "ultra-miniature."

Ball screws with a diameter of less than 16 mm are usually referred to as "miniature",while screws with a diameter of less than 6 mm are usually referred to as "sub-miniature" or "ultra- miniature".

Some manufacturers offer a "compact" series of ball screws.The term usually means that the ball nut uses internal recirculation to make its outside diameter smaller.(Hence,the term "contract. "Despite the name,compact designs often include screws up to 25 mm in diameter - much larger than traditional "miniature" ball screws.

In some respects,the miniature ball screw is identical to the larger "standard" ball screw.For example,miniature ball nuts are available in many of the same styles as standard ball nuts,including flanged,cylindrical(also known as "compact" or "ultra-thin"),or with threaded ends for easy installation into a slider or bench assembly.Ball recirculation can be done inside the ball nut or through an external recirculation method.Lead accuracy and preload class follow the same name regardless of screw diameter.The size parameters,such as the L10 life calculation,buckling load and critical velocity,are the same for both micro and standard ball screws.

Miniature ball screws,like standard ball screws,can be manufactured by rolling or grinding threads.Screws less than 8 mm in diameter are usually produced by grinding,although some manufacturers offer rolled versions of screws as small as 6 mm in diameter.In some micro screw sizes,the journal diameter of the screw is too small to accommodate an appropriately sized end bearing.To solve this problem,the manufacturer can friction weld a larger journal at the screw end to provide enough journal for the support bearing.

Micro ball screws usually use friction-welded ends to accommodate journal machining and support appropriately sized end bearings.

In addition to the small screw diameter,the miniature screw has the advantage over the standard version with the option of very thin leads.The smallest micro screws have a lead of only 0.5 mm,which means that each rotation of the screw produces a stroke of 0.5 mm.This is a significant advantage in applications that require fine-tuning,such as positioning semiconductor wafers or optical devices,or driving small medical pumps and dispensing devices.

Because miniature balls use very small balls for load carrying,preload options are more limited,typically achieving light preload of only 1% to 2%,compared to up to 5% for standard ball screws using the oversized ball preload method.However,micro screws in some ways offer more customization options and more standard variations.For example,a combination of left-handed and right-handed screws(one part of the screw has a left-handed thread and the other part has a right-handed thread)is often available in miniature designs.

Screws and nuts made of stainless steel are also readily available in micro screw products,while standard sizes are few and far between.This can be attributed to the fact that miniature leads usually carry smaller loads,while stainless steel materials cannot withstand the high loads that larger ball leads often transport.

Because of their small leads,miniature ball screws can perform very fine movements,and in vertical applications,these small leads are nearly impossible to reverse drive.Because ball screws operate in metal-to-metal contact,they are not suitable for swing applications,even for miniature sizes where the stroke length is usually small.For oscillating motion applications,a voice coil or piezoelectric ceramic actuator may be a better choice.

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