{"id":742,"date":"2026-06-03T01:48:54","date_gmt":"2026-06-03T01:48:54","guid":{"rendered":"https:\/\/planetary-gearboxes.com\/?p=742"},"modified":"2026-06-03T01:48:54","modified_gmt":"2026-06-03T01:48:54","slug":"planetary-gearbox-cnc-machine-tool-rotary-axis-selection","status":"publish","type":"post","link":"https:\/\/planetary-gearboxes.com\/da\/planetary-gearbox-cnc-machine-tool-rotary-axis-selection\/","title":{"rendered":"Valg af pr\u00e6cisionsplanetgearkasse til roterende akser til CNC-maskiner"},"content":{"rendered":"
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Koreas evige magt<\/span>
\nCNC Machine Tool Application Guide<\/span><\/div>\n

Precision Planetary Gearbox Selection for CNC Machine Tool Rotary Axes \u2014 B\/C\/A Axis and 4th\/5th Axis Guide<\/h1>\n

CNC rotary axes impose requirements that general servo guides do not address. The accuracy of a boring operation depends directly on gearbox backlash at the cutting radius \u2014 not at an arbitrary test point. A 5-axis B-axis under heavy interrupted cut demands torsional stiffness that a general servo application never requires. Flood coolant demands IP65. This guide resolves all three constraints axis by axis.<\/p>\n

Get CNC Axis Specification Support \u2192<\/a><\/p>\n<\/div>\n<\/div>\n<\/section>\n

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Three Requirements That Separate CNC Rotary Axes from General Servo Applications<\/h2>\n

Most precision planetary gearbox selection methodologies are written for general servo automation \u2014 conveyors, robots, indexers. CNC machine tool rotary axes introduce three additional requirements that these guides do not address, and failing to account for any one of them leads to a gearbox specification that is technically correct for torque and speed but wrong for the application.<\/p>\n

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\u2460 Backlash at the Cutting Radius \u2014 Not at a Generic Test Point<\/div>\n

CNC accuracy specifications state tolerances at the workpiece \u2014 at the actual cutting radius, which could be 10mm (small bore) or 300mm (large facing). The same 8 arcmin backlash produces 23\u03bcm of tangential error at R=10mm but 1,163\u03bcm at R=500mm. CNC specifications must always be evaluated at the actual cutting radius, not at a representative intermediate value. Backlash that is acceptable for one operation may fail completely for another on the same machine.<\/p>\n<\/div>\n

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\u2461 Torsional Stiffness Under Cutting Load \u2014 Not Just Positioning Accuracy<\/div>\n

CNC cutting loads are highly variable \u2014 the torque changes instantaneously with chip thickness, material variations, and tool entry\/exit. Under a 380 N\u00b7m peak cutting torque, an EP-ZDE-160 (Ct=38 N\u00b7m\/arcmin) deflects elastically by 10 arcmin \u2014 more than the specified backlash \u2014 producing a tool-position error that servo feedback cannot detect or correct because the motor encoder is on the input side of the gearbox. This load-dependent error is invisible to the servo, directly accumulates in the workpiece, and worsens with cutting force amplitude.<\/p>\n<\/div>\n

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\u2462 Coolant Environment \u2014 IP Rating Determines Service Life<\/div>\n

CNC machine tools use flood coolant at 2\u20138 bar pressure, cutting oil mist, and periodic internal machine washdown. A gearbox installed on an external rotary table positioned under the spindle can receive direct coolant impingement at full pump pressure. IP54 (standard for EP-ZDE\/ZDF\/ZDWE\/ZDWF) protects against directional splashing but not sustained direct jets. Only IP65 (EP-ZDS) withstands the IPX5 test \u2014 6.3mm nozzle at 12.5L\/min from any direction \u2014 which approximates flood coolant conditions on exposed rotary fixtures.<\/p>\n<\/div>\n<\/div>\n<\/section>\n

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\"Kvalitetsfremstilling<\/p>\n

EP series precision planetary gearboxes are 100% tested for backlash at \u00b13% rated torque before shipment. Every unit carries a certified backlash value on its factory documentation \u2014 the traceability required by CNC machine tool OEM quality management systems. Se EP-seriens specifikationer \u2192<\/a><\/div>\n<\/div>\n

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Backlash at Your Cutting Radius \u2014 The Table CNC Engineers Need<\/h2>\n

The following table converts standard planetary gearbox backlash specifications into tangential positioning error at representative CNC cutting radii. All values use the exact formula: E_tangential = R \u00d7 tan(BL \/ (60 \u00d7 180\/\u03c0)). For boring and turning operations where the tool traces a circular path, this tangential error appears directly as roundness deviation on the finished surface.<\/p>\n

\n\n\n\n\n\n\n\n\n
Modreaktion<\/th>\nR=10mm
\nSmall bore<\/span><\/th>\n		R=25mm
\n\u03a650mm bore<\/span><\/th>\n		R=50mm
\n\u03a6100mm bore<\/span><\/th>\n		R=100mm
\n\u03a6200mm face<\/span><\/th>\n		R=200mm
\n\u03a6400mm table<\/span><\/th>\n		EP-serien<\/th>\n<\/tr>\n<\/thead>\n
<3 bueminutter<\/td>\n8.7 \u03bcm<\/td>\n21.8 \u03bcm<\/td>\n43.6 \u03bcm<\/td>\n87.3 \u03bcm<\/td>\n174.5 \u03bcm<\/td>\nCustom \/ special order<\/td>\n<\/tr>\n
<8 bueminut \u2605<\/td>\n23.3 \u03bcm<\/td>\n58.2 \u03bcm<\/td>\n116.4 \u03bcm<\/td>\n232.7 \u03bcm<\/td>\n465.4 \u03bcm<\/td>\nEP-ZDE\/ZDF (60\u2013160mm) \u00b7 EP-ZDS (all)<\/td>\n<\/tr>\n
<12 bueminutter<\/td>\n34.9 \u03bcm<\/td>\n87.3 \u03bcm<\/td>\n174.5 \u03bcm<\/td>\n349.1 \u03bcm<\/td>\n698.1 \u03bcm<\/td>\nEP-ZDE-40 single stage; 2-stage units<\/td>\n<\/tr>\n
<25 bueminutter<\/td>\n72.7 \u03bcm<\/td>\n181.8 \u03bcm<\/td>\n363.6 \u03bcm<\/td>\n727.3 \u03bcm<\/td>\n1,454 \u03bcm<\/td>\nEP-ZDWE\/ZDWF \u2014 right-angle input only<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n

\u2605 Standard EP-ZDE\/ZDF\/ZDS series. Values are maximum backlash error before CNC backlash compensation. With Fanuc\/Siemens backlash compensation active, residual error at slow feed rates is typically <10% of uncompensated value. Values in bold red exceed IT7 tolerance for that bore diameter \u2014 application requires either tighter backlash, compensation, or larger bore tolerance specification.<\/p>\n

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Reading this table for a specific operation<\/div>\n

A VMC 4th axis boring a \u03a6100mm hole (R=50mm) with an EP-ZDE-120 (<8 arcmin) produces a maximum backlash-induced roundness error of 116.4\u03bcm per revolution. With Fanuc Series 0i backlash compensation, this reduces to approximately 12\u201320\u03bcm \u2014 compatible with IT8 tolerance. Without compensation, the same bore at IT7 (25\u03bcm for \u03a6100mm bore) fails. Specify backlash compensation in the CNC program, or upgrade to EP-ZDS to reduce backlash contribution to the error budget.<\/p>\n<\/div>\n<\/section>\n

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CNC Rotary Axis Specifications \u2014 B\/C\/A Axis and 4th\/5th Axis, Axis by Axis<\/h2>\n

The five rotary axis types used in Korean CNC machine tools have different primary design drivers. The same EP series unit that is correct for a 4th-axis trunnion on a VMC will be inadequate for a B-axis on a 5-axis machining centre, and wrong for a C-axis on a turning-milling centre that experiences full turning torques. The axis-by-axis analysis below resolves the correct specification for each.<\/p>\n

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B-AXIS<\/div>\n
5-Axis Machining Centre \u2014 Tilting Rotary Table or Head<\/div>\n<\/div>\n
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Primary requirements:<\/strong>
\nTilt range \u00b190\u00b0 or \u00b1110\u00b0
\nPeak cutting torque: 150\u2013600 N\u00b7m depending on size
\nHeavy interrupted cuts in titanium\/Inconel
\nClamping hold torque: 2\u20133\u00d7 cutting torque
\nIP54 minimum (coolant mist); IP65 for external fixture<\/div>\n
Critical specification:<\/strong>
\nTorsional stiffness dominates above crossover torque
\nZDS-142 crossover: 352 N\u00b7m (BL \u00d7 Ct = 8 \u00d7 44)
\nZDE-160 crossover: 304 N\u00b7m (8 \u00d7 38)
\nFor T_cut > 304 N\u00b7m: elastic error exceeds backlash
\n\u2192 tighter backlash spec won’t help; higher Ct will<\/div>\n
Anbefalet:<\/strong>
\nMedium 5-axis (T_cut \u2264 250 N\u00b7m):
\n\u2192 EP-ZDS-115<\/a>, 20:1, Ct=20 N\u00b7m\/arcmin
\nHeavy 5-axis (T_cut 250\u2013600 N\u00b7m):
\n\u2192 EP-ZDS-142, 20:1, Ct=44 N\u00b7m\/arcmin
\nVery heavy (T_cut > 600 N\u00b7m):
\n\u2192 EP-ZDS-190, 20\u201325:1, Ct=130 N\u00b7m\/arcmin<\/div>\n<\/div>\n
Inertia check:<\/strong> B-axis tilts the entire rotary table or spindle head. For a 50kg tilting table at R=200mm: J_load = 50\u00d70.20\u00b2 = 2.0 kg\u00b7m\u00b2. i_optimal = \u221a(2.0\/0.006) = 18.3 \u2014 confirming 20:1 as the correct ratio. At 20:1, J_reflected = 2.0\/400 = 0.005 kg\u00b7m\u00b2 \u2014 an inertia ratio of 0.83:1 (slightly under-reflected), which is acceptable and allows full servo Kv.<\/div>\n<\/div>\n

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C-AXIS<\/div>\n
Turning-Milling Centre \u2014 Main Spindle Positioning and Mill-Turn C-Axis<\/div>\n<\/div>\n
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Two distinct operating modes:<\/strong>
\nTurning mode: C-axis is the spindle drive \u2014 high torque, continuous rotation, no position precision required
\nMilling\/positioning mode: C-axis indexes to exact angle for off-centre milling \u2014 position accuracy critical<\/div>\n
Precision mode requirements:<\/strong>
\nIndex accuracy: \u00b15\u201315″ of arc (arcseconds)
\n8 arcmin = 480 arcseconds \u2014 far too wide for \u00b15″ target
\nC-axis precision: requires gear + encoder closed-loop
\nThe gearbox sets the accuracy floor that the encoder must overcome through closed-loop correction<\/div>\n
Anbefalet:<\/strong>
\nC-axis positioning (mill-turn):
\n\u2192 EP-ZDE-160 or EP-ZDS-115 at 10\u201316:1
\nBL <8 arcmin; combined with Heidenhain\/Renishaw encoder for \u00b115″ accuracy
\nFlood coolant exposure: specify EP-ZDS-115\/142<\/div>\n<\/div>\n
Critical note on C-axis precision:<\/strong> The <8 arcmin backlash of EP-ZDE\/ZDS corresponds to 480 arcseconds. Turning-milling centres requiring \u00b15″ angular positioning use the gearbox as a torque multiplier only \u2014 the actual angular position is controlled by a scale encoder mounted on the C-axis table, not the motor encoder. The gearbox backlash determines how much pre-load the servo must apply to take up the dead band before position feedback control can take over.<\/div>\n<\/div>\n

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A-AXIS<\/div>\n
Gantry Mill Trunnion \u2014 A-Axis Tilt on Gantry Machining Centre<\/div>\n<\/div>\n
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Karakteristika:<\/strong>
\nTilt range \u00b145\u00b0 to \u00b190\u00b0
\nSpindle plus head assembly: 40\u2013120kg
\nGravity load at maximum tilt: full head weight at R=200\u2013400mm
\nMust hold position against gravity during cutting
\nTypically no clamping brake \u2014 gearbox must hold statically<\/div>\n
Gravity load analysis:<\/strong>
\n60kg spindle head, R=300mm at full tilt:
\nT_gravity = 60 \u00d7 9.81 \u00d7 0.3 = 176.6 N\u00b7m
\nRequired holding (with SF=2.0): 353 N\u00b7m
\nThis is the static load \u2014 add dynamic cutting torque
\nTotal requirement often 400\u2013700 N\u00b7m<\/div>\n
Anbefalet:<\/strong>
\nLight gantry head (40\u201360kg):
\n\u2192 EP-ZDS-115 or ZDE-160, 16\u201320:1
\nHeavy gantry head (80\u2013150kg):
\n\u2192 EP-ZDS-142, 16:1, Ct=44 N\u00b7m\/arcmin
\nVery heavy (150kg+):
\n\u2192 EP-ZDS-190, 16\u201320:1, Ct=130 N\u00b7m\/arcmin<\/div>\n<\/div>\n<\/div>\n

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4th \/ 5th AXIS<\/div>\n
VMC Add-On Rotary Table \u2014 4th\/5th Axis Trunnion Unit<\/div>\n<\/div>\n
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Most common in Korean shops:<\/strong>
\nSeparate add-on rotary tables (4th axis) or dual-axis trunnion (4th+5th)
\nTable diameter: \u03a6200\u2013\u03a6400mm
\nWorkpiece weight: 20\u201380kg typical
\nOften used at full flood coolant \u2014 IP65 critical
\nPositioning only (no continuous turning)<\/div>\n
Accuracy priority:<\/strong>
\n4th axis indexing: typically \u00b110\u201330″ arc
\nCombined with worm or planetary gear and encoder
\nPlanetary approach: compact, efficient, low BL
\nEP-ZDE-120 (Ct=12 N\u00b7m\/arcmin, BL <8): adequate for most VMC 4th axis
\nHeavy workpiece or interrupted cut: upgrade to EP-ZDS-115<\/div>\n
Anbefalet:<\/strong>
\nLight table (20\u201340kg workpiece):
\n\u2192 EP-ZDE-120, 10\u201316:1 (IP54 if internal machine)
\nMedium table (40\u201380kg, coolant exposed):
\n\u2192 EP-ZDS-115, 16\u201320:1, IP65
\nHeavy table (>80kg or heavy interrupted cut):
\n\u2192 EP-ZDS-142, 16:1, IP65, Ct=44<\/div>\n<\/div>\n<\/div>\n<\/section>\n

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Hvorfor torsionsstivhed bestemmer emnetolerance i tunge CNC-operationer<\/h2>\n

Ved afbrudte fr\u00e6sninger, planfr\u00e6sning med store fr\u00e6sere og drejeoperationer p\u00e5 vanskelige materialer varierer sk\u00e6remomentet hurtigt mellem n\u00e6sten nul (ved luftsk\u00e6ring) og fuldt sk\u00e6remoment (ved fuldt indgreb). Hver ind-\/frakoblingscyklus p\u00e5f\u00f8rer en impuls til gearkassen, der for\u00e5rsager elastisk opvikling og tilbagefjedring af udgangsakslen. Denne elastiske oscillation - der sker ved fr\u00e6serens kontaktfrekvens - er det, der for\u00e5rsager overfladeruhedsm\u00f8nstre, polygonm\u00e6rker p\u00e5 borede huller og vibrationer p\u00e5 drejede overflader.<\/p>\n

\n\n\n\n\n\n\n\n\n
Sk\u00e6rescenarie<\/th>\nT_peak (N\u00b7m)<\/th>\nZDE-160
\nelastisk fejl<\/th>\n		ZDS-142
\nelastisk fejl<\/th>\n		ZDS-190
\nelastisk fejl<\/th>\n		Ved R=100 mm
\nZDS-190 fordel<\/th>\n<\/tr>\n<\/thead>\n
Let aluminiumsbekl\u00e6dning<\/td>\n80 Nm<\/td>\n2,1 bueminutter
\n0,122 mm@R=100<\/span><\/td>\n		1,8 bueminutter
\n0,105 mm@R=100<\/span><\/td>\n		0,6 bueminutter
\n0,035 mm@R=100<\/span><\/td>\n		3,4\u00d7<\/td>\n<\/tr>\n
St\u00e5l grovfr\u00e6sning<\/td>\n200 Nm<\/td>\n5,3 bueminutter
\n0,308 mm@R=100<\/span><\/td>\n		4,5 bueminutter
\n0,262 mm@R=100<\/span><\/td>\n		1,5 bueminutter
\n0,087 mm@R=100<\/span><\/td>\n		3,4\u00d7<\/td>\n<\/tr>\n
Tung st\u00e5lboring<\/td>\n380 Nm<\/td>\n10,0 bueminutter
\n0,581 mm@R=100<\/span><\/td>\n		8,6 bueminutter
\n0,500 mm@R=100<\/span><\/td>\n		2,9 bueminutter
\n0,169 mm@R=100<\/span><\/td>\n		3,4\u00d7<\/td>\n<\/tr>\n
Inconel afbrudt snit<\/td>\n600 Nm<\/td>\n15,8 bueminutter
\n0,919 mm@R=100<\/span><\/td>\n		13,6 bueminutter
\n0,791 mm ved R=100<\/span><\/td>\n		4,6 bueminutter
\n0,267 mm@R=100<\/span><\/td>\n		3,4\u00d7<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n

Elastisk fejl = T_peak \/ Ct. ZDE-160: Ct=38; ZDS-142: Ct=44; ZDS-190: Ct=130 N\u00b7m\/arcmin. Ved R=100 mm ved brug af E = R \u00d7 tan(\u03b8\/3438). Servomotorens encoder kan ikke detektere denne elastiske udb\u00f8jning \u2014 den akkumuleres direkte som emnedimensionsfejl.<\/p>\n

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Designm\u00e6ssige implikationer:<\/strong> For CNC-operationer, hvor sk\u00e6reradius overstiger 50 mm, og det maksimale sk\u00e6remoment overstiger 200 N\u00b7m, overstiger den elastiske udb\u00f8jningsfejl fra en ZDE-160 (0,308 mm ved R=100 mm, T=200 N\u00b7m) IT8-tolerancen for de fleste borest\u00f8rrelser. ZDS-190 reducerer dette til 0,087 mm - inden for IT7-toleranceomr\u00e5det. Den samme sl\u00f8rspecifikation (<8 buemin) g\u00e6lder for begge serier; stivhedsforskellen alene giver den n\u00f8jagtighedsforbedring, som en strammere sl\u00f8rspecifikation ikke kan replikere.<\/p>\n<\/div>\n<\/section>\n

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\"H\u00f8jpr\u00e6cisions<\/p>\n

EP-seriens pr\u00e6cisionsplanetgear til CNC-roterende akser leveres med et fabrikscertificeringsdokument, der specificerer sl\u00f8r ved \u00b13% nominelt drejningsmoment, torsionsstivhed Ct og maksimale radiale\/aksiale kraftgr\u00e6nser - de tre specifikationer, der er mest kritiske for verifikation af CNC-maskinv\u00e6rkt\u00f8jsaksers ydeevne. Se tekniske specifikationer for EP-serien \u2192<\/a><\/div>\n<\/div>\n

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K\u00f8lemiddelmilj\u00f8 og IP-klassificering \u2014 Matcher beskyttelse med CNC-virkelighed<\/h2>\n

IP-klassificeringen for en CNC-gearkasse med roterende akse er ikke et generisk valg af \"inde i maskinen = IP54\". Den faktiske k\u00f8lemiddeleksponering afh\u00e6nger af gearkassens position i forhold til k\u00f8lev\u00e6skens str\u00f8mningsvej, maskinens kabinetdesign og om rotationsaksen er integreret i maskinen eller tilf\u00f8jet eksternt. Forkert IP-valg resulterer i den kontamineringsfejl, der er beskrevet i fejl\u00e5rsagsguiden - som i CNC-milj\u00f8er typisk manifesterer sig inden for 2.000-4.000 timer.<\/p>\n

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\u2705 IP54 Tilstr\u00e6kkelig \u2014 EP-ZDE\/ZDF\/ZDWE\/ZDWF<\/div>\n