{"id":1526,"date":"2026-04-08T07:55:27","date_gmt":"2026-04-08T07:55:27","guid":{"rendered":"https:\/\/planetarygeardrive.top\/?p=1526"},"modified":"2026-04-08T08:03:24","modified_gmt":"2026-04-08T08:03:24","slug":"how-to-connect-a-motor-to-a-planetary-gearbox-input-shaft-key-spline-or-hollow","status":"publish","type":"post","link":"https:\/\/planetarygeardrive.top\/ml\/application\/how-to-connect-a-motor-to-a-planetary-gearbox-input-shaft-key-spline-or-hollow\/","title":{"rendered":"How to connect a motor to a planetary gearbox input shaft? Key, spline, or hollow?"},"content":{"rendered":"

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Technical Reference \u00b7 Motor-to-Gearbox Interface<\/p>\n

Planetary Gearbox Input Shaft: IEC Motor Connection, Key vs. Spline vs. Hollow Shaft \u2014 Getting the Interface Right<\/h2>\n

The planetary gearbox input shaft<\/strong> connection between the electric motor and the gearbox is the most frequently underspecified interface in industrial drive system design. Three connection methods are in common use \u2014 each with a different torque capacity, misalignment tolerance, and installation precision requirement. Selecting the wrong one adds vibration, accelerates bearing wear, or causes catastrophic shaft failure at initial start-up.<\/p>\n<\/div>\n

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Drive System \u2014 Exploded Input Interface View<\/p>\n

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<\/p>\n

\n
IEC Motor<\/div>\n
Frame 90\u2013355
\nD-flange or
\nB-flange<\/div>\n<\/div>\n

<\/p>\n

\n
<\/div>\n
interface<\/div>\n<\/div>\n

<\/p>\n

\n
Coupling<\/div>\n
Key \/ Spline \/
\nHollow shaft \/
\nShrink disc<\/div>\n<\/div>\n

<\/p>\n

\n
<\/div>\n
input shaft<\/div>\n<\/div>\n

<\/p>\n

\n
Planetary
\nGearbox<\/div>\n
1\u20134 stage
\nreduction<\/div>\n<\/div>\n

<\/p>\n

\n
<\/div>\n
output<\/div>\n<\/div>\n

<\/p>\n

\n
Driven
\nMachine<\/div>\n
Conveyor \/ Agitator
\n\/ Winch \/ etc.<\/div>\n<\/div>\n<\/div>\n

The input interface (coupling) is the most critical mechanical connection in the drive system \u2014 it transfers all motor torque into the gearbox input shaft and must accommodate any motor-to-gearbox misalignment without generating damaging radial loads on either the motor or the gearbox input bearing.<\/p>\n<\/div>\n

\"\"
\n<\/p>\n

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Type A<\/span><\/p>\n

Solid Input Shaft with Key Connection \u2014 Standard and Most Common<\/h2>\n<\/div>\n

The gearbox input shaft key connection<\/strong> is the most widely used motor-to-gearbox interface in standard industrial applications. The motor shaft has a rectangular keyway machined into it; the coupling hub (or direct coupling) has a matching keyway; a square or rectangular key is inserted to transmit torque through the contact between the key and the keyway walls. The planetary gearbox input shaft bore accepts the motor shaft with the key, and a setscrew or end cap locks the assembly axially.<\/p>\n

The key connection has one significant limitation: it transmits torque through a small contact area between the key and the keyway, creating a stress concentration at the keyway corners. At the very high torques encountered in multi-stage planetary gearbox input shafts (which are at the motor’s full rated torque \u2014 not the multiplied output torque), this stress concentration can initiate fatigue cracking in the shaft at the keyway if the key fit is not correct. The correct key fit is a transition fit in the shaft keyway (slight interference) and a clearance fit in the hub keyway \u2014 this prevents the key from fretting in the shaft while allowing assembly with the hub.<\/p>\n

Application range:<\/strong> Up to 500 Nm at the input shaft in standard IEC motor direct coupling. Above 500 Nm, consider splined or shrink disc connection to avoid key fatigue. Standard for IEC frame sizes 90\u2013280 direct-coupled to planetary gearbox input flange.<\/div>\n<\/div>\n

<\/p>\n

\n
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Type B<\/span><\/p>\n

Splined Input Shaft \u2014 For High Torque and Frequent Assembly\/Disassembly<\/h2>\n<\/div>\n

The splined input shaft planetary gearbox<\/strong> uses a multi-tooth spline profile on both the motor shaft and the gearbox input bore \u2014 typically involute spline per DIN 5480 or ANSI B92.1. The spline distributes torque across all teeth simultaneously, eliminating the stress concentration at keyway corners. Splined connections can transmit 3\u20135\u00d7 the torque of a keyed connection of the same shaft diameter, making them the correct choice for high-torque applications (above 500 Nm at the input shaft) and for applications with frequent motor swaps where a quick-disconnect connection is operationally useful.<\/p>\n

The critical installation requirement for splined input shafts: lubrication. A dry spline assembly under torque fretting \u2014 the microscopic relative motion between spline tooth flanks caused by torque variation \u2014 produces fretting corrosion at the spline contact surfaces within 500\u20131,000 operating hours. Apply a light film of MoS\u2082 grease (Molykote G-n or equivalent) to the spline teeth at every assembly event. Never assemble a splined connection dry.<\/p>\n

Application range:<\/strong> 500\u20135,000 Nm at input shaft. Standard for hydraulic motor connections to planetary gearbox (track drives, winch drives, swing drives) \u2014 hydraulic motor shafts are almost universally splined per SAE J498 or ISO 14.<\/div>\n<\/div>\n

<\/p>\n

\n
\n

Type C<\/span><\/p>\n

Hollow Input Shaft \u2014 Direct Motor Shaft Mounting, No Coupling Required<\/h2>\n<\/div>\n

The hollow input shaft gearbox<\/strong> eliminates the coupling entirely \u2014 the motor shaft passes directly into the gearbox hollow input bore and is clamped by a shrink disc (or key) inside the housing. The motor flange bolts directly to the gearbox input flange, creating a compact integrated motor-gearbox assembly with no intermediate coupling components.<\/p>\n

This is the standard configuration for IEC motor to planetary gearbox connection<\/strong> in all gearbox families designed for direct motor mounting \u2014 including our complete inline and right-angle ranges. The hollow input bore is sized to accept standard IEC motor shaft diameters (from 19 mm for IEC 80 to 75 mm for IEC 355) with tolerances matching the motor shaft tolerance class. The gearbox input flange bolt circle matches the IEC standard motor flange B14 or B5 pattern for the corresponding frame size.<\/p>\n

The primary advantage of the hollow input shaft configuration \u2014 beyond the elimination of coupling components \u2014 is the elimination of coupling alignment errors. Because the motor shaft is directly supported inside the gearbox input bore, the motor shaft and the gearbox input shaft are inherently coaxial. This removes the radial load that coupling misalignment imposes on the gearbox input bearing \u2014 one of the most common avoidable failure sources in coupled installations.<\/p>\n

Our inline planetary gearbox series<\/a> is available with hollow input shaft for all IEC motor frame sizes from 80 to 355, covering motor shaft diameters from 19 mm to 75 mm. The input flange bolt pattern matches both B5 (face mount, motor flange bolts through the flange into the gearbox housing) and B14 (face mount, gearbox flange bolts into the motor mounting face) configurations. For the selection between these and other mounting configurations, see our mounting configuration selection guide<\/a>.<\/p>\n<\/div>\n

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IEC Motor Frame to Gearbox Input \u2014 Standard Shaft Diameter Reference<\/h2>\n
\n\n\n\n\n\n\n\n\n\n
IEC Frame<\/th>\nShaft \u00d8 (mm)<\/th>\nTypical Power (kW)<\/th>\nInput Shaft Torque Range<\/th>\n<\/tr>\n<\/thead>\n
90<\/td>\n24<\/td>\n0.75\u20132.2<\/td>\n5\u201315 Nm<\/td>\n<\/tr>\n
132<\/td>\n38<\/td>\n5.5\u201311<\/td>\n35\u201375 Nm<\/td>\n<\/tr>\n
180<\/td>\n48<\/td>\n15\u201330<\/td>\n100\u2013200 Nm<\/td>\n<\/tr>\n
225<\/td>\n60<\/td>\n37\u201355<\/td>\n240\u2013360 Nm<\/td>\n<\/tr>\n
280<\/td>\n75<\/td>\n75\u2013132<\/td>\n480\u2013850 Nm<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n

At 1,500 RPM nominal. Above IEC 280, splined or shrink disc input is recommended over keyed connection.<\/p>\n<\/div>\n

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Motor-to-Gearbox Interface Confirmed Before You Order \u2014 IEC Frame, Shaft \u00d8, and Connection Type.<\/h2>\n

Motor IEC frame size, rated power, and required output torque and ratio. We confirm the correct hollow bore diameter, flange pattern, and connection type \u2014 and return a quotation with dimensional drawing within 24 hours. MOQ 1 unit.<\/p>\n

Get a Motor-Matched Gearbox Quote \u2192<\/a><\/p>\n

\ud83d\udce7 sales@planetarygeardrive.top \u00b7 Canada Planetary Gear Drive Co., Ltd \u00b7 ISO 9001:2015<\/p>\n<\/div>\n

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Related Searches<\/p>\n

planetary gearbox input shaft \u00b7 planetary gearbox motor coupling \u00b7 gearbox input shaft key connection \u00b7 splined input shaft planetary gearbox \u00b7 IEC motor to planetary gearbox connection<\/p>\n<\/div>\n

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Torque Limiter and Backstop at the Input Shaft \u2014 When to Add These Components<\/h2>\n

Two optional components are frequently fitted at the gearbox input shaft position in specific applications: a torque limiter and a backstop (also called an anti-reverse device or one-way clutch). Understanding when each is required \u2014 and why adding them to applications that do not need them creates its own problems \u2014 is part of correct input shaft specification.<\/p>\n

A torque limiter<\/strong> is a slip coupling inserted between the motor shaft and the gearbox input \u2014 it disengages (slips) when the transmitted torque exceeds a set threshold, protecting both the motor and the gearbox from overload events caused by a machine jam, foreign object ingress, or operator error. Torque limiters are appropriate for applications with frequent jam risk (auger conveyors, wood chippers, shredders) where the overload occurs regularly enough that designing the gearbox to withstand it at SF 3.0+ is not economically viable. They are not appropriate for applications with infrequent but severe overload \u2014 such as crane hoist jams \u2014 where the torque limiter’s friction characteristics allow high transient torques before slipping, providing no meaningful protection at the jam event’s peak torque.<\/p>\n

A backstop<\/strong> at the input shaft prevents the driven machine from reverse-running when the motor is de-energised \u2014 critical for inclined conveyors where a loaded belt would run backward under gravity without the backstop. The backstop is a one-way roller ramp or sprag clutch that transmits torque freely in the drive direction but locks instantly against reverse rotation. In planetary gearbox applications, the backstop is most effective when mounted on the input shaft (at the motor) rather than the output shaft \u2014 because the input shaft rotates at higher speed, the backstop disengages more smoothly during the transition from powered to freewheeling operation. Mounting the backstop on the output shaft in a high-torque application creates a backstop that must absorb the full output torque at the moment of engagement \u2014 potentially damaging the backstop ramps.<\/p>\n

Our inline planetary gearbox series<\/a> is available with input-shaft torque limiter and backstop provisions as optional factory-fitted components across all frame sizes. Specify the required torque limiter slip torque and the backstop rated input torque at the time of order \u2014 these components require confirmation of the exact input shaft configuration and cannot be retrofitted after gearbox manufacturing.<\/p>\n

editor\uff1aWM<\/p>\n<\/div>","protected":false},"excerpt":{"rendered":"

Technical Reference \u00b7 Motor-to-Gearbox Interface Planetary Gearbox Input Shaft: IEC Motor Connection, Key vs. Spline vs. Hollow Shaft \u2014 Getting the Interface Right The planetary gearbox input shaft connection between the electric motor and the gearbox is the most frequently underspecified interface in industrial drive system design. Three connection methods are in common use \u2014 […]<\/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":[2097],"tags":[2265,2263,2264],"class_list":["post-1526","post","type-post","status-publish","format-standard","hentry","category-gearbox-selecton-guide","tag-iec-motor-to-planetary-gearbox-connection","tag-planetary-gearbox-input-shaft","tag-planetary-gearbox-motor-coupling"],"_links":{"self":[{"href":"https:\/\/planetarygeardrive.top\/ml\/wp-json\/wp\/v2\/posts\/1526","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/planetarygeardrive.top\/ml\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/planetarygeardrive.top\/ml\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/planetarygeardrive.top\/ml\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/planetarygeardrive.top\/ml\/wp-json\/wp\/v2\/comments?post=1526"}],"version-history":[{"count":3,"href":"https:\/\/planetarygeardrive.top\/ml\/wp-json\/wp\/v2\/posts\/1526\/revisions"}],"predecessor-version":[{"id":1530,"href":"https:\/\/planetarygeardrive.top\/ml\/wp-json\/wp\/v2\/posts\/1526\/revisions\/1530"}],"wp:attachment":[{"href":"https:\/\/planetarygeardrive.top\/ml\/wp-json\/wp\/v2\/media?parent=1526"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/planetarygeardrive.top\/ml\/wp-json\/wp\/v2\/categories?post=1526"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/planetarygeardrive.top\/ml\/wp-json\/wp\/v2\/tags?post=1526"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}