Ball screws transmit force through recirculating rolling balls, while conventional lead screws use sliding contact between matching threads. That difference shapes friction, wear, drive torque and maintenance.
Ball Screw vs Lead Screw: The Short Answer
A ball screw is usually the first candidate for frequent, efficient positioning. A conventional lead screw is worth evaluating for slower or intermittent adjustment when a simpler assembly meets the load and accuracy requirements. Either type can be appropriate for demanding loads if the specific screw-and-nut assembly is rated for the duty.
Browse LILY Bearing’s Ball Screws and Nuts and Lead Screws and Nuts categories to compare available configurations.
How the Mechanisms Differ
Ball Screws: Rolling Contact
In a ball screw, balls carry load between helical raceways on the screw and nut. A return system recirculates the balls as the assembly moves. The low-friction contact helps limit drive losses, especially during repeated travel. Lubrication, contamination control and correct ball-nut selection remain important.
Lead Screws: Sliding Contact
A lead screw moves its nut through sliding contact along matching threads. Bronze, brass and engineered polymers are common nut materials, selected for load, wear, noise, temperature and lubrication. Acme is one lead screw thread form; other lead screw profiles are also used.
LILY lists Precision Acme Lead Screws and Nuts alongside Ultra-Precision Lead Screws and Nuts. These are different product families; the matching nut and its performance must be evaluated separately from the screw.
Ball Screw vs Acme Screw
An Acme screw is a sliding-contact lead screw with a 29° included thread angle in the standard U.S. Acme form. It commonly uses a metal or polymer nut, whereas a ball screw uses recirculating balls. For intermittent adjustment, an Acme assembly can be economical; for repeated travel, rolling contact often makes the ball screw more efficient. ASME B1.5 — Acme Screw Threads covers Acme thread forms and dimensions, including multi-start arrangements used for greater travel per revolution. Backlash and nut wear still depend on the chosen fit and assembly.
For available thread configurations, browse LILY’s Acme Lead Screws and Nuts.
Selection Table for OEM Design
Use the comparison below to narrow the options. Actual capacity, heat, life, backlash and price depend on the specific screw, matching nut, and operating conditions.
Efficiency and Required Drive Torque
For equal axial force and lead, the screw with higher forward efficiency needs less driving torque. The following calculation uses two assumed efficiencies to show the size of that difference.
For steady motion: T = F × L / (2π × η). In SI units, T is N·m, F is N, and L is m/rev. Using U.S. customary units, T (lbf·in) = F (lbf) × L (in/rev) / (2π × η). The symbol η represents forward efficiency as a decimal.
The two assumed efficiencies produce a 2.25-fold difference in screw input torque. Motor sizing must also account for acceleration and losses elsewhere in the drive.
Load, Life, Heat and Support Limits
For ball screws, fatigue-life calculations use the assembly’s rated dynamic load capacity and equivalent operating load; peak or shock loading calls for a separate static check. Sliding lead screws instead need attention to nut wear, thread loading, frictional heating and, where relevant, the nut material’s pressure–velocity (PV) limit. Neither calculation can be completed from screw lead alone.
Also check screw buckling under compression and the critical rotational speed of the actual length and end-support arrangement. On a long axis, these limits can dictate diameter before motor power does.
Accuracy, Backlash and Repeatability
Lead accuracy measures how closely actual travel follows the specified travel over a stated distance. Backlash is clearance-related relative motion during reversal; repeatability describes consistency when returning to a position. Catalog travel accuracy describes the screw shaft; the positioning accuracy of an assembled axis is a separate specification. ISO 3408-3:2006 describes acceptance conditions and permissible deviations for ball screws.
For a positioning axis, specify the required travel tolerance and reversal error separately. Preloaded ball nuts and anti-backlash lead nuts can reduce clearance, but their stiffness, friction and wear characteristics differ. The support bearings, coupling, guides and structure also influence measured lost motion.
Backdriving, Self-Locking and Safety
A suspended load can backdrive a high-efficiency ball screw. A low-lead sliding screw may resist backdriving, but a single-start thread is not proof of self-locking. Lead angle, friction, lubrication, vibration and wear all matter. Use a properly rated brake, counterbalance or equivalent holding system wherever unexpected motion poses a risk.
Lead, Pitch and Travel per Revolution
What Is Ball Screw Lead?
Ball screw lead is the nominal axial distance the nut travels relative to the screw in one revolution. Pitch is the axial spacing between corresponding points on adjacent thread forms. For a single-start screw, lead equals pitch. For multiple starts, lead = pitch × number of starts. The same geometric relationship applies to multi-start lead screws.
Linear speed equals lead multiplied by rotational speed. A 5 mm/rev screw at 600 rpm moves nominally 3,000 mm/min (50 mm/s, about 118 in/min). A larger lead covers more distance per turn, while increasing the ideal drive torque for the same force and efficiency.
LILY Catalog Examples
The examples below show differences in thread geometry and catalog travel accuracy across four specific screw shafts. Because their dimensions and constructions differ, these figures are not a controlled accuracy comparison between ball screws and lead screws.
The ten-start JJADAAAAC lead screw, for example, lists 1 in/rev of travel. At 300 rpm, its calculated travel rate would be 300 in/min; allowable operating speed still depends on supports, length, load and the matching nut. See LILY’s Fast-Travel Precision Acme Lead Screws and Nuts category for related configurations.
Two Application Examples and an RFQ Checklist
High-Cycle Automated Positioning
Consider a production transfer axis that accelerates, stops and reverses repeatedly. Friction losses and positioning performance accumulate over many cycles, so a ball screw is a sensible starting point. Compare the actual load spectrum and lead before sizing the motor; check support stiffness, critical speed and lubricant service requirements.
Occasional Fixture Adjustment
For a fixture adjusted only a few times per shift, a sliding lead screw may give better value. A bronze or suitable polymer nut can be simple and quiet when its wear and heat limits fit the duty. If the fixture must hold a vertical or externally applied load, assess backdriving and the required holding device.
OEM RFQ Checklist: What to Send
For replacements, include the original part number or a dimensioned drawing: matching screw diameter and nominal lead does not ensure nut or end-support interchangeability. Send the completed requirements to LILY Bearing using the Request a Quote form.
FAQ
Can I Replace a Lead Screw with a Ball Screw Without Changing the Motor?
Sometimes. Compare motor speed and available torque at the new screw lead, then check the nut, supports and mounting dimensions. Higher forward efficiency may lower running torque, but a ball screw may also backdrive more readily, changing the required brake or holding arrangement.
Is a Ball Screw Worth the Extra Cost?
Yes, for many high-duty-cycle axes. Reduced friction can lower drive losses and support long service life when the assembly is sized and maintained correctly. For an occasional adjustment, a suitable lead screw may be the better overall value.
What Is a Ball Screw Used For?
Ball screws convert rotary motion into controlled linear travel in machine-tool feed axes, automated positioning stages and repeated-transfer mechanisms. They are especially useful when efficiency and frequent cycling matter, provided the chosen assembly meets load, speed and accuracy requirements.
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