{"id":2386,"date":"2026-06-26T03:46:08","date_gmt":"2026-06-26T03:46:08","guid":{"rendered":"https:\/\/helicalcutgears.top\/?p=2386"},"modified":"2026-06-26T03:46:08","modified_gmt":"2026-06-26T03:46:08","slug":"helical-gear-bore-keyway-specification-din-6885","status":"publish","type":"post","link":"https:\/\/helicalcutgears.top\/sk\/helical-gear-bore-keyway-specification-din-6885\/","title":{"rendered":"\u0160pecifik\u00e1cia otvoru a dr\u00e1\u017eky pre k\u013e\u00fa\u010d pre \u0161pir\u00e1lov\u00e9 ozuben\u00e9 koleso \u2014 Rozmery k\u013e\u00fa\u010da DIN 6885, tolerancia H7 a pr\u00edru\u010dka pre pripojenia hriade\u013ea"},"content":{"rendered":"
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Helical Gear Bore and Keyway Specification \u2014 DIN 6885 Key Dimensions, Bore Tolerances and Shaft Connections<\/h1>\n

The bore and keyway of a \u0161pir\u00e1lov\u00e9 ozuben\u00e9 koleso<\/strong> determine whether the gear transmits torque reliably to the shaft throughout its service life, or slips, fretts, and fails at the shaft-hub interface long before the gear teeth wear out. Choosing the correct bore tolerance (H7, K7, or interference P7), keyway dimensions from DIN 6885-1, and hub wall thickness is a specification decision with equal importance to the gear tooth parameters \u2014 yet it is frequently handled with less rigour than the tooth design itself.<\/p>\n

Confirm Bore Specification for Your Gear \u2192<\/a><\/p>\n<\/div>\n<\/div>\n

Three Shaft Connection Types for Helical Gears<\/h2>\n

A \u0161pir\u00e1lov\u00e9 ozuben\u00e9 koleso<\/strong> is connected to its shaft by one of three mechanisms, each suited to a different torque range and assembly frequency:<\/p>\n

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Parallel Key (DIN 6885-1) \u2014 Most Common<\/strong><\/p>\n

A rectangular steel key sits in matched keyways in both the shaft and the \u0161pir\u00e1lov\u00e9 ozuben\u00e9 koleso<\/strong> bore, transmitting torque through the key’s shear area. Bore tolerance H7 (clearance fit) \u2014 the gear can be slid on and off the shaft by hand or light press. Suitable for gears requiring periodic removal for maintenance. This is the default connection for industrial \u0161pir\u00e1lov\u00e9 ozuben\u00e9 koles\u00e1<\/strong> in M3\u2013M32.<\/p>\n<\/div>\n

Interference Fit (No Key) \u2014 High Torque<\/strong><\/p>\n

Bore tolerance P7 or R7 \u2014 the \u0161pir\u00e1lov\u00e9 ozuben\u00e9 koleso<\/strong> is pressed or shrink-fitted onto the shaft with 0.01\u20130.05 mm of radial interference. Torque is transmitted by friction at the shaft-bore interface; no key is used. Advantages: no stress concentration from keyway; full bore area available for torque; no fretting at key contact. Disadvantages: requires hydraulic press or heating for installation and removal. Used for permanent high-torque connections in heavy industry.<\/p>\n<\/div>\n

Spline (DIN 5480) \u2014 High Torque + Frequent Disassembly<\/strong><\/p>\n

An involute spline (DIN 5480) with many small teeth around the bore perimeter distributes the torque over a large contact area, allowing much higher torque than a single key at the same shaft diameter, while remaining easily disassembled. Used for high-torque vehicle driveshaft connections, crane gearboxes, and any application where the \u0161pir\u00e1lov\u00e9 ozuben\u00e9 koleso<\/strong> must be removed and reinstalled repeatedly without special equipment.<\/p>\n<\/div>\n<\/div>\n

DIN 6885-1 Parallel Key Dimensions \u2014 Reference Table<\/h2>\n

DIN 6885 Part 1 specifies the standard parallel key (Passfeder) dimensions for a given shaft diameter. The key width b and height h are selected from the standard table based on the shaft diameter at the \u0161pir\u00e1lov\u00e9 ozuben\u00e9 koleso<\/strong> bore:<\/p>\n

\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n
Shaft Diameter Range (mm)<\/th>\nKey Width b (mm)<\/th>\nKey Height h (mm)<\/th>\nDepth in Shaft t\u2081 (mm)<\/th>\nDepth in Hub t\u2082 (mm)<\/th>\n<\/tr>\n<\/thead>\n
17\u201322<\/td>\n6<\/td>\n6<\/td>\n3.5<\/td>\n2.8<\/td>\n<\/tr>\n
22\u201330<\/td>\n8<\/td>\n7<\/td>\n4.0<\/td>\n3.3<\/td>\n<\/tr>\n
30\u201338<\/td>\n10<\/td>\n8<\/td>\n5.0<\/td>\n3.3<\/td>\n<\/tr>\n
38\u201344<\/td>\n12<\/td>\n8<\/td>\n5.0<\/td>\n3.3<\/td>\n<\/tr>\n
44\u201350<\/td>\n14<\/td>\n9<\/td>\n5.5<\/td>\n3.8<\/td>\n<\/tr>\n
50\u201358<\/td>\n16<\/td>\n10<\/td>\n6.0<\/td>\n4.3<\/td>\n<\/tr>\n
58\u201365<\/td>\n18<\/td>\n11<\/td>\n7.0<\/td>\n4.4<\/td>\n<\/tr>\n
65\u201375<\/td>\n20<\/td>\n12<\/td>\n7.5<\/td>\n4.9<\/td>\n<\/tr>\n
75\u201385<\/td>\n22<\/td>\n14<\/td>\n9.0<\/td>\n5.4<\/td>\n<\/tr>\n
85\u201395<\/td>\n25<\/td>\n14<\/td>\n9.0<\/td>\n5.4<\/td>\n<\/tr>\n
95\u2013110<\/td>\n28<\/td>\n16<\/td>\n10.0<\/td>\n6.4<\/td>\n<\/tr>\n
110\u2013130<\/td>\n32<\/td>\n18<\/td>\n11.0<\/td>\n7.4<\/td>\n<\/tr>\n
130\u2013150<\/td>\n36<\/td>\n20<\/td>\n12.0<\/td>\n8.4<\/td>\n<\/tr>\n
150\u2013170<\/td>\n40<\/td>\n22<\/td>\n13.0<\/td>\n9.4<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n

Source: DIN 6885-1:2019 (Form A, flat top key, rounded ends). t\u2081 = keyway depth in shaft, t\u2082 = keyway depth in hub (\u0161pir\u00e1lov\u00e9 ozuben\u00e9 koleso<\/strong> bore). The key height h projects into both shaft and hub keyways; the total engagement depth = t\u2081 + t\u2082 \u2248 h with a small clearance at the key top.<\/p>\n

Bore Tolerance Selection \u2014 H7, K7 and P7 Explained<\/h2>\n

\"helical<\/p>\n

Helical gear shaft connection \u2014 the bore tolerance (H7 clearance, K7 transition, or P7 interference) determines the assembly method and torque capacity at the bore-shaft interface. The DIN 6885-1 key transmits torque in H7 clearance fit assemblies; interference fit connections transmit torque by friction without any key<\/p>\n

\n\n\n\n\n\n\n\n\n\n
Bore Tolerance (ISO 286-1)<\/th>\nFit Type<\/th>\nClearance or Interference at \u230050 mm<\/th>\nMet\u00f3da mont\u00e1\u017ee<\/th>\nUve\u010fte kedy<\/th>\n<\/tr>\n<\/thead>\n
H7<\/td>\nClearance (with h6 shaft)<\/td>\n+0.000 \/ +0.025 mm clearance<\/td>\nHand push or light mallet; key transmits torque<\/td>\nStandard removable \u0161pir\u00e1lov\u00e9 ozuben\u00e9 koleso<\/strong>; key required for torque<\/td>\n<\/tr>\n
K7<\/td>\nTransition (with k6 shaft)<\/td>\n\u22120.002 \/ +0.023 mm (transition)<\/td>\nLight press; key reinforces torque capacity<\/td>\nReduced vibration\/fretting risk vs H7; moderate disassembly frequency<\/td>\n<\/tr>\n
M7<\/td>\nTransition \/ light interference<\/td>\n\u22120.009 \/ +0.016 mm<\/td>\nPress (hydraulic preferred)<\/td>\nInfrequent removal; better torque retention than H7+key for reversing loads<\/td>\n<\/tr>\n
P7<\/td>\nInterference<\/td>\n\u22120.026 \/ \u22120.001 mm interference<\/td>\nHydraulic press (10\u201330 tonnes); or heat the gear 150\u2013200\u00b0C<\/td>\nPermanent or rare-removal connection; heavy-duty reversing loads; no key needed at moderate torque<\/td>\n<\/tr>\n
H6<\/td>\nPrecision clearance<\/td>\n+0.000 \/ +0.016 mm (tighter than H7)<\/td>\nSelective fit \u2014 must pair with matched shaft<\/td>\nPrecision indexing or register; servo gearboxes where concentricity is critical<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n
Fretting on H7 clearance fit under reversing load:<\/strong> A \u0161pir\u00e1lov\u00e9 ozuben\u00e9 koleso<\/strong> with H7 bore and a standard DIN key under cyclic torque reversal is susceptible to fretting corrosion at the bore-shaft interface \u2014 even though the key transmits the torque, the micro-movement at the clearance gap between bore and shaft causes oxidative wear that gradually enlarges the bore. For reversing load \u0161pir\u00e1lov\u00e9 ozuben\u00e9 koleso<\/strong> applications (crane hoists, printing presses, bidirectional conveyors), Korea Ever-Power recommends either K7 or M7 transition fit to minimise bore-shaft micro-movement, or a dual-key arrangement to increase the bore-shaft interference contribution through the key contact.<\/div>\n

Minimum Wall Thickness \u2014 Bore to Root Circle<\/h2>\n

The wall thickness between the \u0161pir\u00e1lov\u00e9 ozuben\u00e9 koleso<\/strong> bore and the gear root circle must be sufficient to prevent cracking at the tooth root during heat treatment (thermal gradients through thin sections cause residual stresses that can lead to quench cracking) and to prevent hub face yielding under the contact pressure of the press-fit connection:<\/p>\n

Minimum wall thickness: t_wall \u2265 2.5 \u00d7 Mn (Korea Ever-Power standard for carburized gears)
\nt_wall \u2265 2.0 \u00d7 Mn (minimum for QT gears under moderate load)<\/p>\n

Checking the wall:
\nRoot circle diameter d_f = Mn \u00d7 (z \u2212 2.5) \/ cos \u03b2 (standard dedendum 1.25 \u00d7 Mn)
\nMaximum bore diameter d_bore_max = d_f \u2212 2 \u00d7 t_wall_min<\/p>\n

Example: M8, z=30, \u03b2=20\u00b0, carburized:
\nd_f = 8 \u00d7 (30 \u2212 2.5) \/ cos20\u00b0 = 8 \u00d7 27.5 \/ 0.9397 = 234.1 mm
\nt_wall_min = 2.5 \u00d7 8 = 20 mm
\nd_bore_max = 234.1 \u2212 2 \u00d7 20 = 194.1 mm<\/p>\n

A bore larger than 194 mm on this example \u0161pir\u00e1lov\u00e9 ozuben\u00e9 koleso<\/strong> would violate the minimum wall thickness and risk quench cracking during carburizing, or hub face yielding under press-fit installation. Korea Ever-Power checks the wall thickness constraint at the drawing review stage and flags any bore-module combination that violates the minimum before production begins.<\/p>\n

Double Keyway \u2014 For Very High Torque on Large Module Gears<\/h2>\n

When the torque requirement exceeds the capacity of a single DIN 6885-1 key at the given shaft diameter, two keys placed diametrically opposite (180\u00b0 apart) double the total key contact area and halve the shear stress per key. Double keyways are standard for \u0161pir\u00e1lov\u00e9 ozuben\u00e9 koles\u00e1<\/strong> with shaft diameters above approximately 150 mm in high-torque drives. The two keyways must be positioned at exactly 180\u00b0 \u2014 measured and verified by CMM after machining. An angular error between the two keyways greater than \u00b10.1\u00b0 creates unequal key loading that effectively reduces the double-key torque capacity to approximately 1.6\u00d7 rather than 2\u00d7 the single-key value.<\/p>\n

DIN 5480 Spline Connection \u2014 When to Choose Spline Over Key<\/h2>\n

A DIN 5480 involute spline hub replaces the single keyway with 10\u201380 small involute-profile spline teeth around the bore perimeter. The torque capacity of a spline exceeds a single key by 3\u20138\u00d7 at the same shaft diameter, because the torque is distributed over many teeth rather than concentrated on one key. Select spline over key when:<\/p>\n