{"id":658,"date":"2026-05-29T05:17:07","date_gmt":"2026-05-29T05:17:07","guid":{"rendered":"https:\/\/planetary-gearboxes.com\/?p=658"},"modified":"2026-05-29T05:17:43","modified_gmt":"2026-05-29T05:17:43","slug":"planetary-gearbox-backlash-grades-explained-p0-p1-p2","status":"publish","type":"post","link":"https:\/\/planetary-gearboxes.com\/nl\/planetary-gearbox-backlash-grades-explained-p0-p1-p2\/","title":{"rendered":"Planetary Gearbox Backlash Explained \u2014 P0, P1, P2 Grades"},"content":{"rendered":"

<\/p>\n
\"planetary<\/p>\n
\n
Engineering Reference \u00b7 P0 P1 P2 \u00b7 Calculation Guide \u00b7 Measurement Protocol<\/div>\n

Planetary Gearbox Backlash Explained \u2014
\nP0, P1, P2 Grades and What They Mean for Positioning<\/h1>\n

Engineers either over-specify P0 for every axis \u2014 paying a 30\u201350% unit cost premium they do not need \u2014 or under-specify P2 for precision servo axes, buying hardware that systematically undermines machine accuracy from day one. This guide explains exactly what planetary gearbox backlash<\/strong> is, how arcminute grades translate into real positioning error at the workpiece, and which grade every application type actually requires.<\/p>\n

View EP-AB P0 Precision Series \u2192
\n<\/a><\/p>\n<\/div>\n<\/section>\n

<\/p>\n

\n

What Backlash Is \u2014 and the Common Misconceptions That Lead to Wrong Specifications<\/h2>\n
\n
\n

Backlash is the angular displacement of the gearbox output shaft when the input reverses direction and the output does not yet move \u2014 the “dead zone” at every direction reversal, caused by the clearance between meshing gear teeth. It is measured in arcminutes (1 arcminute = 1\/60\u00b0) at the output shaft, with the input shaft locked.<\/p>\n

Backlash is not a manufacturing defect.<\/strong> Every planetary gearbox requires tooth clearance for two unavoidable physical reasons: the lubricant film between gear teeth needs physical space to form \u2014 zero clearance means the oil film is squeezed out and metal-to-metal contact occurs. And thermal expansion of the gear teeth during operation requires clearance to accommodate the dimensional change without seizure. A gearbox with genuinely zero backlash would overheat and seize within minutes of reaching operating temperature.<\/p>\n

What the P0\/P1\/P2 grade system controls is how much<\/em> backlash \u2014 the precision of the tooth clearance. Tighter clearance (lower backlash) requires more precise gear grinding, closer dimensional tolerance in the housing bores, and selective assembly pairing of gear sets \u2014 all of which increase manufacturing cost. The engineering discipline is to specify the minimum grade that your application actually requires, not the minimum that the catalogue offers.<\/p>\n

The “zero backlash” misconception: <\/strong>
\nSystems marketed as “zero backlash” achieve this through mechanical preload \u2014 spring-loaded or mechanically-biased components that keep gear flanks in constant contact. Preload reduces effective backlash but introduces constant friction and wear, reducing efficiency and service life. Standard Korea Ever-Power EP planetary gearboxes use engineered tooth clearance (P0\/P1\/P2) rather than preload \u2014 the specified backlash is the genuine clearance, not a preloaded approximation.<\/span><\/div>\n

The practical implication: when a servo axis with a P0 \u22641 arcmin gearbox shows positioning drift, the cause is almost never the gearbox backlash \u2014 it is more likely servo tuning, thermal expansion of the machine structure, or spindle runout. Backlash shows as a specific signature: consistent angular error in one direction only<\/em> immediately following a direction reversal, equal to the backlash magnitude. If the error is random, grows with temperature, or appears in both directions simultaneously, the cause is not backlash.<\/p>\n<\/div>\n

<\/p>\n
\n

Backlash \u2014 The Physical Mechanism<\/p>\n

Input rotates \u2192 Output moves normallyInput reverses \u2192 (BACKLASH ZONE)
\nInput shaft moves
\nOutput shaft: STATIONARY
\n(clearing tooth clearance)
\n\u2190\u2190\u2190 \u03b8_backlash \u2190\u2190\u2190<\/p>\n

Input continues reversing \u2192
\nOutput shaft begins moving again<\/p>\n

Measured: \u03b8_backlash = angular gap
\nat output shaft during reversal<\/p>\n<\/div>\n

Backlash shows as a consistent angular error after direction reversal \u2014 not random, not temperature-dependent, always equal to the clearance angle.<\/div>\n<\/div>\n
\n
\n
\u22641′<\/div>\n
P0 \u2014 Micro<\/div>\n
CNC\/Robot<\/div>\n<\/div>\n
\n
\u22643′<\/div>\n
P1 \u2014 Reduced<\/div>\n
Servo\/Pkg<\/div>\n<\/div>\n
\n
\u22645′<\/div>\n
P2 \u2014 Standard<\/div>\n
General<\/div>\n<\/div>\n
\n
\u22648′<\/div>\n
Fixed (AE\/AER)<\/div>\n
Food\/Outdoor<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/section>\n

<\/p>\n

\n

The Arcminute Scale \u2014 Translating Grade Numbers into Real Positioning Error<\/h2>\n
\n
\n

Understanding planetary gearbox backlash explained in arcminute terms \u2014 rather than degrees \u2014 is essential for accurate specification. The arcminute is the unit of angular measurement used for backlash because it is appropriately sized \u2014 1 arcminute equals 1\/60 of one degree. For a typical servo application, backlash values span 1 to 30 arcminutes. Expressing these values in degrees (0.017\u00b0 to 0.5\u00b0) is unwieldy; expressing them in radians (0.000291 to 0.00873 rad) loses intuitive scale. Arcminutes sit at exactly the right resolution for practical specification and measurement.<\/p>\n

The linear positioning error produced by a given backlash depends on the radius at which the error is measured \u2014 the lever arm between the gearbox output shaft and the workpiece or tool contact point. The relationship is:<\/p>\n

\n

BACKLASH \u2192 LINEAR ERROR FORMULA<\/p>\n

\u0394x = r \u00d7 \u03b8_backlash (radians)<\/div>\n
r = radius from output shaft to measurement point (mm)
\n\u03b8 (rad) = arcmin \u00d7 \u03c0 \/ (180 \u00d7 60) = arcmin \u00d7 0.000291
\nAt r=100 mm, 1 arcmin \u2192 \u0394x = 100 \u00d7 0.000291 = 0.029 mm<\/span><\/div>\n<\/div>\n

Engineering implication:<\/strong> the same gearbox backlash produces different linear errors at different radii. P1 \u22643 arcmin on a rotary table driving a 50 mm radius workpiece produces 0.044 mm error \u2014 within IT9 tolerance for aluminium parts. The same P1 on a 200 mm radius table produces 0.175 mm \u2014 outside IT9 tolerance for any material. This is why backlash grade must be calculated from the actual working radius, not read from a general application table.<\/p>\n<\/div>\n

\n

Backlash Grade \u2192 Linear Positioning Error at Different Radii<\/p>\n

\n\n\n\n\n\n\n\n\n\n\n
Grade \/ Backlash<\/th>\nr=25 mm<\/th>\nr=50 mm<\/th>\nr=100 mm<\/th>\nr=200 mm<\/th>\n<\/tr>\n<\/thead>\n
P0 \u00b7 \u22641 arcmin<\/td>\n\u22640.007<\/td>\n\u22640.015<\/td>\n\u22640.029<\/td>\n\u22640.058<\/td>\n<\/tr>\n
P1 \u00b7 \u22643 arcmin<\/td>\n\u22640.022<\/td>\n\u22640.044<\/td>\n\u22640.087<\/td>\n\u22640.175<\/td>\n<\/tr>\n
P2 \u00b7 \u22645 arcmin<\/td>\n\u22640.036<\/td>\n\u22640.073<\/td>\n\u22640.145<\/td>\n\u22640.291<\/td>\n<\/tr>\n
AE\/AER \u00b7 \u22648 arcmin<\/td>\n\u22640.058<\/td>\n\u22640.116<\/td>\n\u22640.233<\/td>\n\u22640.465<\/td>\n<\/tr>\n
Economic \u00b7 6\u20138 arcmin<\/td>\n0.044\u20130.058<\/td>\n0.087\u20130.116<\/td>\n0.175\u20130.233<\/td>\n0.349\u20130.465<\/td>\n<\/tr>\n
Worm typical \u00b7 15\u201330 arcmin<\/td>\n0.11\u20130.22<\/td>\n0.22\u20130.44<\/td>\n0.44\u20130.87<\/td>\n0.87\u20131.75<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n

All error values in mm. Errors are reversal errors \u2014 the lost motion when direction is changed. Use r = distance from output shaft centreline to workpiece or tool contact point.<\/p>\n<\/div>\n<\/div>\n<\/section>\n

<\/p>\n

\n

P0, P1, P2 \u2014 How the Grades Are Defined and What Produces the Difference<\/h2>\n
\n
\n

The three precision grades reflect three different manufacturing tolerance bands applied to the same gear geometry. P0 is not a different type of gearbox \u2014 it is the same planetary design produced to tighter dimensional tolerances throughout the manufacturing process. Understanding what manufacturing steps produce each grade helps in understanding why the cost increases with grade.<\/p>\n

\n
\n
P0 \u2014 Micro Backlash<\/span>
\nSingle \u22641′ \u00b7 Two-stage \u22643′<\/span><\/div>\n

Gear teeth ground to minimum functional clearance. 100% selective assembly: each gear set is measured after grinding and paired with a ring gear whose bore deviation complements the tooth deviation to produce a total tooth clearance within \u22641 arcmin. Every unit measured at the output shaft before delivery \u2014 certificate issued with each gearbox confirming the measured value.<\/p>\n

Cost premium vs P2: approx. 30\u201350% \u00b7 Applications: CNC axes, robot joints, register control<\/div>\n<\/div>\n
\n
P1 \u2014 Reduced Backlash<\/span>
\nSingle \u22643′ \u00b7 Two-stage \u22645′<\/span><\/div>\n

Close-tolerance gear grinding within a wider band than P0 \u2014 achievable without 100% selective assembly. The gear grinding process produces consistent tooth profiles within a tolerance that ensures the assembled total stays within \u22643 arcmin. Batch sampling rather than 100% individual measurement. Cost-efficient for applications requiring better-than-standard precision without the extreme tightness of P0.<\/p>\n

Cost premium vs P2: approx. 15\u201325% \u00b7 Applications: servo positioners, packaging axes, printing register<\/div>\n<\/div>\n
\n
P2 \u2014 Standard Backlash<\/span>
\nSingle \u22645′ \u00b7 Two-stage \u22647′<\/span><\/div>\n

Normal production tolerance gear grinding. Standard assembly process without special pairing or 100% individual measurement. Produces the baseline tooth clearance that the housing, bearing, and gear geometry naturally achieve without additional tolerance control steps. Correct specification for all non-precision servo axes and general actuators.<\/p>\n

Baseline cost \u00b7 Applications: general actuators, auxiliary servo axes, non-precision drives<\/div>\n<\/div>\n<\/div>\n
Korea Ever-Power factory verification: <\/strong>
\nAll Korea Ever-Power EP precision series are measured at the output shaft before delivery. For P0, a backlash certificate is issued with every unit confirming the measured value \u2014 not just a grade conformance statement. The EP-AB P0 series<\/a> certificate shows the actual measured backlash (e.g. “0.82 arcmin measured at output shaft, 14 Dec 2025”) \u2014 verifiable at commissioning by measuring the new unit before installation.<\/span><\/div>\n<\/div>\n
\"EP-AE
\n<\/p>\n
\n
What Changes Between P2, P1, and P0<\/div>\n
\n
\u25b8<\/span><\/p>\n
Gear grinding tolerance:<\/strong> P0 requires tighter tooth profile tolerance (\u00b12\u20133 \u03bcm vs \u00b15\u20138 \u03bcm for P2)<\/div>\n<\/div>\n
\u25b8<\/span><\/p>\n
Housing bore tolerance:<\/strong> P0 requires tighter concentricity on gear carrier bearing bores and ring gear seat bore<\/div>\n<\/div>\n
\u25b8<\/span><\/p>\n
Selective assembly (P0 only):<\/strong> gears are measured after grinding and paired to complement deviations within the \u22641 arcmin total<\/div>\n<\/div>\n
\u25b8<\/span><\/p>\n
Inspection level:<\/strong> P0 requires 100% individual unit measurement; P1\/P2 use batch sampling with defined AQL<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/section>\n

<\/p>\n

\n

Series Without P Grades \u2014 Fixed Backlash and When That Is Correct<\/h2>\n

Not all Korea Ever-Power series use the P0\/P1\/P2 grade system. Some series have a fixed backlash specification that does not change with any ordering option \u2014 either because the series design produces a fixed tolerance regardless of manufacturing adjustment, or because the application class the series targets does not require grade selection. Understanding which series lack P grades prevents specification errors.<\/p>\n

\n
\n

EP-AFH<\/a> \u2014 Fixed \u22641 arcmin Standard<\/h3>\n

Every EP-AFH unit, at every frame size (060\u2013240 mm) and every ratio (3\u2013100:1), is manufactured to \u22641 arcmin backlash as its only specification \u2014 there is no grade code because there is no lower-tier option. The entire series is built to P0-equivalent quality. Specifying EP-AFH eliminates the P grade selection step: \u22641 arcmin is guaranteed at delivery. Backlash up to 3,805 N\u00b7m at 240 mm frame.<\/p>\n<\/div>\n

\n

EP-AE\/AER<\/a> \u2014 Fixed \u22648 arcmin (single), \u226412 (two-stage)<\/h3>\n

The large-flange series targets applications where IP67 protection or large overturning moment resistance is the primary requirement \u2014 food processing, outdoor conveyors, wet wash zones. Backlash precision is secondary and \u22648 arcmin fixed is adequate for all these drive types. No P grade selection available \u2014 attempting to specify P0 or P1 on AE\/AER is not a valid option.<\/p>\n<\/div>\n

\n

EP-AH\/AHK New Line \u2014 Fixed 1\u20132 arcmin<\/h3>\n

The New Line heavy-duty series achieves 1\u20132 arcmin backlash as its inherent manufacturing standard \u2014 the structural housing and precision gear train designed for 9,585 N\u00b7m service produce this backlash as a result of their manufacturing process, without a selectable P grade option. Adequate for all heavy industrial rotary tables and crane slewing drives where P0-class precision is not a functional requirement.<\/p>\n<\/div>\n

\n

Economic Line<\/a> \u2014 6\u20138 arcmin (inline), 10\u201312 (right-angle)<\/h3>\n

Economic Line targets induction motor and stepper motor applications where the drive system itself does not use closed-loop position control. Backlash at 6\u20138 arcmin is irrelevant for conveyor speed control, agitator drives, and open-loop positioning. No P grade option \u2014 specifying P0 on Economic Line is a category error; use EP-AB or EP-AF precision series if backlash below 5 arcmin is required.<\/p>\n<\/div>\n<\/div>\n<\/section>\n

<\/p>\n

\n

Matching Backlash Grade to Application \u2014 The Complete Decision Table<\/h2>\n

With planetary gearbox backlash explained from first principles, the correct grade selection flows from three inputs: (1) the required positioning accuracy at the workpiece or tool tip, (2) the working radius (lever arm), and (3) what percentage of the total error budget the gearbox backlash is allowed to consume. Work through the formula \u0394x = r \u00d7 \u03b8 (radians) first, then cross-reference to the table below.<\/p>\n

\n\n\n\n\n\n\n\n\n\n\n\n
Sollicitatie<\/th>\nRequired Accuracy<\/th>\nWorking Radius<\/th>\nGrade<\/th>\nKorea Ever-Power Series<\/th>\n<\/tr>\n<\/thead>\n
5-axis titanium rotary table<\/td>\n\u00b10.02\u00b0 (1.2′)<\/td>\n100\u2013200 mm<\/td>\nP0<\/td>\nEP-AFH<\/a> (no grade code needed)<\/td>\n<\/tr>\n
Collaborative robot (all joints)<\/td>\n\u00b10.02\u00b0 (1.2′)<\/td>\n250\u20131,000 mm<\/td>\nP0<\/td>\nEP-AB P0<\/a> 042\u2013090<\/td>\n<\/tr>\n
CNC register correction axis<\/td>\n\u00b10.05\u00b0 (3′)<\/td>\n50\u2013100 mm<\/td>\nP0 or P1<\/td>\nEP-AB P1 \/ EP-AF P1<\/a><\/td>\n<\/tr>\n
Packaging VFFS forming axis<\/td>\n\u00b10.1\u00b0 (6′)<\/td>\n30\u201380 mm<\/td>\nP1<\/td>\nEP-AB P1 \/ EP-AF P1<\/td>\n<\/tr>\n
General servo positioner \/ turntable<\/td>\n\u00b10.15\u00b0 (9′)<\/td>\n50\u2013150 mm<\/td>\nP2<\/td>\nEP-BAB P2<\/a><\/td>\n<\/tr>\n
Food conveyor head drive<\/td>\nSpeed only<\/td>\nN\/A<\/td>\nNo grade<\/td>\nEP-AER IP67 (6\u20138′ fixed) or Economic Line<\/td>\n<\/tr>\n
Heavy rotary table (large workpiece)<\/td>\n\u00b10.1\u00b0 (6′)<\/td>\n200\u2013400 mm<\/td>\n1\u20132′ fixed<\/td>\nEP-AH New Line (1\u20132′ inherent)<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n
The over-specification cost penalty: <\/strong>
\nA 12-axis CNC machine tool with 4 precision axes (rotary table, B-axis \u00d72, and one linear register axis) and 8 auxiliary axes (chip conveyor, coolant, pallet shuttle, doors, ATC carousel) costs approximately 30\u201340% more in gearbox BOM if all 12 axes are specified at P0. Applying P0 to the 4 precision axes and P2 or Economic Line to the 8 auxiliary axes delivers the same machine performance at significantly lower component cost \u2014 the auxiliary axes cannot benefit from P0 precision because their functions (conveyor speed, door position, coolant flow) are not affected by backlash below \u00b10.15\u00b0.<\/span><\/div>\n<\/section>\n

<\/p>\n

\n

How Backlash Grows in Service \u2014 Wear Mechanics and the Replacement Threshold<\/h2>\n
\n
\n

Backlash does not remain at its delivery value throughout service \u2014 it grows as gear tooth flanks wear at the reversal contact point. Understanding the wear mechanics helps engineers set realistic service life expectations and design appropriate monitoring intervals.<\/p>\n

The wear mechanism:<\/strong> During normal driving motion (before reversal), the driven flank of each planet gear tooth is in continuous rolling contact with the driven flank of the ring gear \u2014 lubricated contact, manageable wear rate. At the instant of direction reversal, the previously unloaded coast flank of the planet gear tooth makes impact contact with the coast flank of the ring gear tooth as the clearance is closed. This reversal impact is a micro-shock: a brief high-contact-stress event that produces localised surface fatigue (pitting) on both tooth flanks. Over millions of reversals, the accumulated pitting increases the effective tooth clearance \u2014 which manifests as growing backlash.<\/p>\n

The wear rate depends strongly on: the applied torque at reversal (higher torque = higher impact contact stress), the reversal frequency (more reversals per hour = more impact events per hour), the lubrication condition (degraded grease = higher metal-to-metal contact during impact), and the inertia ratio (higher load inertia = higher kinetic energy in the impact event).<\/p>\n

\n

BACKLASH GROWTH PROFILE \u2014 P0 GEARBOX<\/p>\n

Hours 0\u20135,000: Delivery value \u22641.0′
\nHours 5,000\u201312,000: Gradual wear, ~1.2\u20131.4′
\nHours 12,000\u201318,000: Accelerating, ~1.5\u20131.8′
\nHours 18,000\u201320,000: Near threshold, ~1.9\u20132.0′
\nHours 20,000+: Replacement recommendedThreshold: 2\u00d7 delivery value (\u22642.0′ for P0)
\nAt 2\u00d7: functional accuracy is measurably
\ndegraded and replacement warranted.<\/p>\n<\/div>\n<\/div>\n

Factors that accelerate wear beyond this profile: operating continuously at 90\u2013110% of rated torque, inertia ratio above 10:1 (higher impact energy at reversal), poor grease condition (seal degradation in contaminated environments), and high reversal frequency (robot joints at 3-shift operation reach 10\u00d7 the reversal count of CNC table drives).<\/p>\n<\/div>\n

\n
\n
Korea Ever-Power Recommended Monitoring Protocol<\/div>\n
\n
\n
Annual measurement<\/div>\n
Measure output backlash with input shaft locked. Apply light torque in both directions. Record angular displacement. Compare to delivery certificate value.<\/div>\n<\/div>\n
\n
Warning at 1.5\u00d7 delivery value<\/div>\n
Schedule replacement at next planned maintenance window. Continue operation with increased monitoring frequency (quarterly instead of annual).<\/div>\n<\/div>\n
\n
Replace at 2\u00d7 delivery value<\/div>\n
At this point, functional positioning accuracy is measurably degraded for P0 specifications. Replace before next planned production run or at next scheduled downtime.<\/div>\n<\/div>\n
\n
Seal inspection (annual)<\/div>\n
Check shaft seal for grease leakage. Grease leakage means the seal is compromised \u2014 contamination can enter and dramatically accelerate wear. Replace at first sign of leakage.<\/div>\n<\/div>\n<\/div>\n<\/div>\n
\n
EP-BAB sealed-grease example:<\/div>\n

The EP-BAB precision planetary series<\/a> uses permanently sealed grease \u2014 no periodic re-lubrication is required. The sealed construction also prevents the contamination-induced wear acceleration that affects non-sealed gearboxes in Korean factory environments with metallic dust, coolant mist, or food product residue.<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/section>\n

\"why<\/p>\n

\n

Two-Stage Backlash Accumulation \u2014 Why P0 Single-Stage \u22641′ Becomes P0 Two-Stage \u22643′<\/h2>\n
\n
\n

The most frequently misunderstood backlash specification is the two-stage value. Engineers encountering “P0: single-stage \u22641 arcmin, two-stage \u22643 arcmin” for the first time often ask whether this means two-stage has worse precision \u2014 why does adding a stage triple the specification? The answer lies in how backlash from multiple stages combines at the output shaft.<\/p>\n

The correct accumulation formula<\/strong> (not a simple sum of the two individual stages):<\/p>\n

\n

TWO-STAGE BACKLASH ACCUMULATION<\/p>\n

\u03b8_total \u2248 \u03b8_stage2 + (\u03b8_stage1 \/ i_stage2)where:
\n\u03b8_stage1 = input stage backlash (arcmin)
\n\u03b8_stage2 = output stage backlash (arcmin)
\ni_stage2 = output stage ratio<\/p>\n

Example (P0, each stage 0.9′):
\ni_stage2 = 5
\n\u03b8_total = 0.9 + (0.9 \/ 5)
\n= 0.9 + 0.18
\n= 1.08 arcmin<\/p>\n

Conservative upper bound at max values:
\n\u03b8_total = 1.0 + (1.0 \/ 3) [i_stage2=3 minimum]
\n= 1.0 + 0.33 = 1.33 arcmin<\/p>\n

Korea Ever-Power specifies \u22643 arcmin for P0
\ntwo-stage \u2014 providing margin for worst-case
\nstage ratio combinations and manufacturing
\nvariation over production batches.<\/p>\n<\/div>\n<\/div>\n

Why the output stage dominates:<\/strong> The input stage backlash is divided by the output stage ratio before adding to the output stage backlash. At a typical output stage ratio of i=5, a 1 arcmin input stage backlash contributes only 0.2 arcmin at the final output shaft \u2014 one-fifth of the input stage value. The output stage backlash contributes its full value (1 arcmin) directly. This is why precision at the output stage matters more than precision at the input stage for two-stage gearbox specifications.<\/p>\n

The same logic applies to right-angle gearboxes with a bevel stage: the bevel stage contribution is divided by the bevel stage ratio before adding to the planetary stage output. However, bevel stage ratios are typically 1:1 (the bevel only changes direction without ratio change) \u2014 so in right-angle integrated gearboxes, the bevel contribution adds directly without division. This is accounted for in Korea Ever-Power’s EP-ABR\/ADR\/AFR specifications, which measure total backlash at the right-angle output shaft.<\/p>\n<\/div>\n

\n
\n

STAGE CONTRIBUTION DIAGRAM<\/p>\n

Motor input
\n\u2193
\n[STAGE 1] \u03b8\u2081 = 1.0 arcmin
\n\u2193 (reduced by i\u2082 = 5)
\ncontribution = 1.0\/5 = 0.2′ at output
\n\u2193
\n[STAGE 2] \u03b8\u2082 = 1.0 arcmin
\n\u2193 (adds directly at output)
\ncontribution = 1.0′ at output
\n\u2193
\nTOTAL at output = 0.2 + 1.0 = 1.2 arcmin<\/span>Key insight:
\nStage 1 backlash is attenuated by i\u2082
\nStage 2 backlash is NOT attenuated
\n\u2192 Output stage quality matters most<\/p>\n<\/div>\n<\/div>\n
\n
Why \u22643′ is the P0 two-stage specification:<\/div>\n

The specification provides margin above the typical calculated value (~1.0\u20131.2 arcmin) to account for manufacturing variation across production batches, the full range of ratio combinations (where lower i\u2082 increases stage-1 contribution), and realistic worst-case tolerance stack-ups. Korea Ever-Power guarantees \u22643 arcmin at the output shaft; typical delivered values for P0 two-stage units are 1.1\u20131.8 arcmin.<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/section>\n

<\/p>\n

\n

Right-Angle Gearbox Backlash \u2014 Why the Bevel Stage Is Already Included<\/h2>\n
\n
\n

The most persistent backlash misconception in Korean machine tool design is the belief that right-angle planetary gearboxes add bevel gear backlash on top of the planetary stage specification \u2014 that a P0 right-angle unit is effectively P1 at the output because of the extra bevel contribution. This is incorrect for Korea Ever-Power integrated right-angle series, and the measurement method explains why.<\/p>\n

For EP-ABR, EP-ADR, and EP-AFR<\/a>, the P0\/P1\/P2 backlash is measured at the right-angle output shaft \u2014 the actual shaft that connects to the machine. The measurement procedure locks the motor input shaft, applies a small torque to the right-angle output shaft in each direction, and records the angular displacement. This single measurement captures the combined contribution of all<\/em> stages \u2014 planetary stages and bevel stage together \u2014 in one result.<\/p>\n

The stated P0 \u22641 arcmin for EP-ABR is the total system backlash at the right-angle output shaft, including bevel. It is not the planetary-stage backlash with an additional bevel contribution on top. When a Korea Ever-Power certificate says “EP-ABR090 P0: 0.76 arcmin measured at output shaft,” that 0.76 arcmin includes the bevel contribution \u2014 and the total is within the P0 specification.<\/p>\n

When to ask any supplier for clarification: <\/strong>
\nIf a supplier states a backlash value for a right-angle gearbox, always verify: “Is this measured at the final right-angle output shaft with the bevel stage active?” If the answer is “this is the planetary stage specification \u2014 the bevel adds extra,” the total output backlash is higher than stated. Korea Ever-Power provides the measurement point confirmation in writing on the delivery certificate for all right-angle series.<\/span><\/div>\n<\/div>\n
\"Korea<\/p>\n
\n\n\n\n\n\n\n\n\n
Configuration<\/th>\nP0 Spec<\/th>\nMeasured at<\/th>\n<\/tr>\n<\/thead>\n
EP-AB (inline)<\/td>\n\u22641 arcmin<\/td>\nInline output shaft \u2713<\/td>\n<\/tr>\n
EP-ABR P0 (R\/A)<\/td>\n\u22641 arcmin<\/td>\nR\/A output shaft \u2713 (bevel included)<\/td>\n<\/tr>\n
EP-AFR P0 (R\/A)<\/td>\n\u22641 arcmin<\/td>\nR\/A output shaft \u2713 (bevel included)<\/td>\n<\/tr>\n
Competitor: “P0 planetary + bevel”<\/td>\n\u22641′ stage only<\/td>\nBefore bevel \u26a0 (+3\u20135′ extra)<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/div>\n<\/div>\n<\/section>\n

<\/p>\n

\n

How to Specify Backlash Grade When Ordering \u2014 and Frequently Asked Questions<\/h2>\n

<\/p>\n

\n

KOREA EVER-POWER ORDER CODE FORMAT \u2014 BACKLASH GRADE EXAMPLE<\/p>\n

EP-AB<\/span> \u00b7 090<\/span> \u00b7 i25<\/span> \u00b7 S2<\/span> \u00b7 P1<\/span><\/div>\n
\n
Series: EP-AB<\/div>\n
Frame: 090 mm<\/div>\n
Ratio: i=25:1<\/div>\n
Shaft: S2 (keyway)<\/div>\n
Grade: P1<\/div>\n<\/div>\n
Omitting the grade code: Korea Ever-Power defaults to P2 (standard backlash) if no grade is specified in the order. Always include the grade code if P0 or P1 is required \u2014 do not rely on verbal confirmation.<\/div>\n<\/div>\n
\n
\n

Q<\/span>
\nCan I upgrade a delivered P1 gearbox to P0 in the field?<\/h3>\n

No. Backlash grade is set entirely during manufacture \u2014 it is a property of the gear tooth geometry, housing tolerances, and assembly pairing, not a setting that can be adjusted after manufacture. A P1 gearbox cannot be converted to P0 by any field procedure. If the installed backlash proves insufficient for the application, the gearbox must be replaced with a P0 unit. This is why the Korea Ever-Power application team always recommends confirming the required grade from the positioning specification before ordering, rather than starting with a lower grade and upgrading later.<\/p>\n<\/div>\n

\n

Q<\/span>
\nWhat is the difference between backlash and positioning repeatability?<\/h3>\n

Backlash is a mechanical property of the gearbox \u2014 the angular clearance between gear teeth. Positioning repeatability is a system-level property of the complete servo axis \u2014 the ability to return to the same commanded position after multiple approach cycles. A servo axis with a closed-loop linear scale encoder can achieve sub-micron repeatability even with a P2 (5 arcmin) gearbox, because the encoder compensates for backlash through closed-loop feedback. Backlash matters most when: (1) the servo uses motor encoder feedback only (not output-side encoder), or (2) the axis must maintain accuracy through power-off events, or (3) the system must achieve accuracy in both approach directions without reversal compensation. For applications using output-side linear scale encoders, backlash grade selection has negligible effect on positioning repeatability \u2014 the encoder compensates it.<\/p>\n<\/div>\n

\n

Q<\/span>
\nWhy does my P0 gearbox show more than 1 arcmin backlash after 3 years of operation \u2014 is it defective?<\/h3>\n

Not necessarily. Backlash growth from \u22641 arcmin at delivery to 1.3\u20131.5 arcmin after 3 years (approximately 7,500 operating hours at three-shift operation) is within the expected wear profile for P0 gearboxes. The service life target of \u22642 arcmin at 20,000 hours means some measurable growth is expected during service. Compare the measured value to the delivery certificate \u2014 growth within 1.5\u00d7 the delivery value is normal wear, not a defect. If the growth is rapid (reaching 1.5\u00d7 in less than 3,000 hours), investigate: the gearbox may have been operated above rated torque, the inertia ratio may be excessive, or the shaft seal may have failed allowing contamination into the grease.<\/p>\n<\/div>\n

\n

Q<\/span>
\nHow does a worm gear reducer specify backlash, compared to planetary P0\/P1\/P2?<\/h3>\n

Worm gear reducers use a fundamentally different approach to positioning control: the worm mechanism’s self-locking property provides position holding without needing tight tooth clearance, and the sliding contact geometry makes sub-5-arcmin backlash impractical to manufacture at reasonable cost. Most worm reducer catalogues do not specify backlash in arcminutes at all \u2014 they specify “tooth contact ratio” or simply note that the design is “backlash-minimised.” When backlash is specified for worm gear reducers<\/a>, values of 10\u201330 arcmin are typical. This is why worm reducers are not used for any servo axis where closed-loop positioning in both directions is required \u2014 the backlash budget simply does not allow it. The P0\/P1\/P2 grading system is specific to precision planetary (and some precision helical) gearboxes where rolling-contact gear geometry makes sub-3-arcmin backlash manufacturable and economically viable.<\/p>\n<\/div>\n<\/div>\n<\/section>\n

<\/p>\n

\n

Specify the Right Backlash Grade \u2014 Korea Ever-Power Application Support<\/h2>\n

Korea Ever-Power’s Korean application team calculates the required backlash grade from your positioning specification and working radius, confirms the appropriate series, and issues a grade certificate with every P0 and P1 delivery \u2014 in Korean, same working day.<\/p>\n

EP-AB P0 Precision Inline \u2192
\n<\/a>
\nEP-AFH Fixed \u22641 arcmin \u2192
\n<\/a><\/div>\n<\/section>\n

Redacteur: Cxm
\n<\/main><\/p>","protected":false},"excerpt":{"rendered":"

Engineering Reference \u00b7 P0 P1 P2 \u00b7 Calculation Guide \u00b7 Measurement Protocol Planetary Gearbox Backlash Explained \u2014 P0, P1, P2 Grades and What They Mean for Positioning Engineers either over-specify P0 for every axis \u2014 paying a 30\u201350% unit cost premium they do not need \u2014 or under-specify P2 for precision servo axes, buying hardware […]<\/p>","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_et_pb_use_builder":"","_et_pb_old_content":"","_et_gb_content_width":"","footnotes":""},"categories":[965],"tags":[],"class_list":["post-658","post","type-post","status-publish","format-standard","hentry","category-application-and-technical-guid"],"_links":{"self":[{"href":"https:\/\/planetary-gearboxes.com\/nl\/wp-json\/wp\/v2\/posts\/658","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/planetary-gearboxes.com\/nl\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/planetary-gearboxes.com\/nl\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/planetary-gearboxes.com\/nl\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/planetary-gearboxes.com\/nl\/wp-json\/wp\/v2\/comments?post=658"}],"version-history":[{"count":2,"href":"https:\/\/planetary-gearboxes.com\/nl\/wp-json\/wp\/v2\/posts\/658\/revisions"}],"predecessor-version":[{"id":660,"href":"https:\/\/planetary-gearboxes.com\/nl\/wp-json\/wp\/v2\/posts\/658\/revisions\/660"}],"wp:attachment":[{"href":"https:\/\/planetary-gearboxes.com\/nl\/wp-json\/wp\/v2\/media?parent=658"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/planetary-gearboxes.com\/nl\/wp-json\/wp\/v2\/categories?post=658"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/planetary-gearboxes.com\/nl\/wp-json\/wp\/v2\/tags?post=658"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}