{"id":1667,"date":"2026-09-02T09:08:34","date_gmt":"2026-09-02T09:08:34","guid":{"rendered":"https:\/\/metalite.net\/?p=1667"},"modified":"2026-09-02T09:19:16","modified_gmt":"2026-09-02T09:19:16","slug":"output-shaft-vs-flange-output-right-angle-planetary-gearbox","status":"publish","type":"post","link":"https:\/\/metalite.net\/de_at\/application\/output-shaft-vs-flange-output-right-angle-planetary-gearbox\/","title":{"rendered":"Right Angle Planetary Gearbox: Output Shaft vs Flange Output"},"content":{"rendered":"
\n

Right Angle Planetary Gearbox: Output Shaft vs Flange Output<\/h2>\n

Output configuration is one of those specification decisions that gets made once and can’t easily be undone. Keyed shaft, output flange, hollow shaft\u2014these are manufacturing choices, not field-adjustable settings. Order the wrong one and you’re looking at a new unit, a custom adapter, or a machine modification that costs more than the gearbox itself. Most engineers know this in principle; the challenge is knowing which configuration is actually right for a given application before the order goes in.<\/p>\n

This article covers the three output configurations available in right angle planetary gearboxes, the engineering reasons to choose each one, and the specific factors that should drive the decision\u2014torque, moment load, assembly length, concentricity requirements, and what you’re connecting to.<\/p>\n

\"\"<\/p>\n

The Three Output Configurations<\/h2>\n

Before getting into the selection logic, it helps to be precise about what each configuration is and what it isn’t.<\/p>\n

Keyed output shaft<\/strong> is a cylindrical shaft extending from the gearbox output, with a parallel keyway machined into it. A driven component\u2014a coupling hub, a sprocket, a timing pulley, a pinion gear\u2014slides onto the shaft and is secured by the key and a set screw, clamp, or end plate. This is the most common output configuration and the one that connects to the widest range of standard industrial components.<\/p>\n

Output flange<\/strong> (sometimes called a flange output or face output) is a precision-machined circular flange face on the output housing, with a pilot diameter for centering and a bolt circle for attachment. The driven component\u2014a rotary table body, an indexer housing, a robot link, or a custom machine component\u2014bolts directly to the flange face. The gearbox output shaft may be present as a short stub inside the flange, or the connection may be purely through the flange face and bolts.<\/p>\n

Hollow shaft<\/strong> (also hollow bore output) eliminates the output shaft entirely. Instead, the driven shaft passes through a precision bore in the gearbox output section and is clamped or keyed inside it. No separate coupling is needed; the gearbox mounts directly onto the driven shaft.<\/p>\n

These are not interchangeable after manufacture. The housing geometry, bearing arrangement, and output interface are all designed around the selected configuration. Specify this at the time of order.<\/p>\n

\"\"<\/p>\n

Keyed Output Shaft: When to Use It<\/h2>\n

The keyed shaft is the default for most applications, and for good reason. It connects to standard off-the-shelf components without custom machining. Sprockets, pulleys, jaw couplings, disc couplings, and gear pinions are all designed around standard shaft diameters and keyway dimensions. If your application drives through any of these components, a keyed shaft output is the natural choice.<\/p>\n

The shaft output also provides flexibility. The same gearbox can connect to different driven components by changing the coupling or sprocket\u2014useful for machines that may be reconfigured or for applications where the end use isn’t fully defined at design time.<\/p>\n

The limitations of a keyed shaft output are mechanical. The shaft extension creates a cantilevered overhang, and any radial force applied to that overhang generates a bending moment at the output bearing. The further the driven component is from the bearing face, the larger the moment arm and the higher the bending stress on the shaft and bearing. Most gearbox datasheets specify the rated radial load at a reference point on the shaft\u2014typically at a defined distance from the bearing face. If your sprocket or pulley is mounted further out than that reference point, the allowable radial load is lower than the rated value. This is one of the most commonly overlooked constraints in shaft output selection.<\/p>\n

Keyway backlash is also worth noting. A parallel key in a keyway has clearance\u2014typically 0.01\u20130.04 mm on each side\u2014which contributes a small amount of torsional play at the output connection. For most applications this is negligible. For high-precision servo positioning where every source of angular error matters, it’s worth acknowledging as part of the total system error budget.<\/p>\n

\"\"<\/p>\n

Output Flange: When It’s the Better Choice<\/h2>\n

An output flange is the right choice when the driven component mounts directly to the gearbox face rather than connecting through a coupling. The most common cases:<\/p>\n

Rotary tables and indexers.<\/strong> The gearbox drives a table or indexer body that bolts directly to the output flange. The flange pilot diameter centers the driven component precisely, and the bolt circle provides a stiff, rigid attachment. There’s no coupling, no shaft extension, no separate centering operation required.<\/p>\n

Robot links and joints.<\/strong> In articulated robot designs, adjacent links bolt directly to each other through the gearbox output flange. The flange provides both the torque transmission path and the structural connection between links.<\/p>\n

Custom machine components with high moment loads.<\/strong> When the driven component applies a significant bending moment to the gearbox output\u2014a long arm, a cantilevered load, a large inertia mass mounted off-center\u2014a flange output distributes that moment load across the flange bolt circle and the housing face rather than concentrating it at a single shaft extension point. This gives flange outputs inherently higher moment load capacity than shaft outputs of the same frame size.<\/p>\n

The output flange also eliminates the coupling in the drivetrain. This reduces total backlash (no coupling clearance), reduces total assembly length (no coupling hub and spacer), and removes one potential alignment error source. For precision servo applications where the driven component can be designed to interface directly with the gearbox flange, this is a meaningful advantage.<\/p>\n

The limitation: the driven component must be designed or adapted to match the flange bolt circle and pilot diameter. Standard off-the-shelf components like sprockets and pulleys don’t have flange mounting holes. An output flange gearbox driving a chain sprocket requires a custom adapter plate, which adds cost and may introduce the same concentricity and backlash issues the flange was intended to eliminate. Match the output configuration to what you’re actually connecting to.<\/p>\n

\n\n\n\n\n\n\n\n\n\n\n\n
Factor<\/th>\nKeyed Shaft Output<\/th>\nOutput Flange<\/th>\nHollow Shaft<\/th>\n<\/tr>\n<\/thead>\n
Connection to standard components<\/strong><\/td>\nExcellent \u2014 sprockets, pulleys, couplings<\/td>\nRequires custom or adapted components<\/td>\nRequires matching shaft diameter<\/td>\n<\/tr>\n
Moment load capacity<\/strong><\/td>\nLimited by shaft extension length<\/td>\nHigh \u2014 distributed across bolt circle<\/td>\nHigh \u2014 shaft fully supported in bore<\/td>\n<\/tr>\n
Backlash at output interface<\/strong><\/td>\nKeyway clearance adds slight play<\/td>\nNo coupling \u2014 no added backlash<\/td>\nNo coupling \u2014 no added backlash<\/td>\n<\/tr>\n
Assembly length<\/strong><\/td>\nLonger \u2014 shaft + coupling adds length<\/td>\nShorter \u2014 no shaft extension<\/td>\nShortest \u2014 gearbox mounts on driven shaft<\/td>\n<\/tr>\n
Concentricity control<\/strong><\/td>\nCoupling alignment required<\/td>\nPilot diameter self-aligns<\/td>\nBore fits shaft directly<\/td>\n<\/tr>\n
Anti-rotation requirement<\/strong><\/td>\nNone \u2014 gearbox fixed to frame<\/td>\nNone \u2014 gearbox fixed to frame<\/td>\nRequired \u2014 torque arm needed<\/td>\n<\/tr>\n
Typical applications<\/strong><\/td>\nConveyors, general drives, belt drives<\/td>\nRotary tables, robot joints, indexers<\/td>\nShaft-mounted drives, roll drives<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n

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Hollow Shaft: When It Solves a Real Problem<\/h2>\n

The hollow shaft output is underused relative to how often it would be the right answer. Engineers default to shaft output because it’s familiar, then spend time designing coupling arrangements that add length, add backlash, and require alignment procedures that wouldn’t be necessary with a hollow shaft design.<\/p>\n

Hollow shaft is the right choice when the gearbox mounts directly onto a driven shaft\u2014a roll shaft, a conveyor shaft, a spindle\u2014and the driven shaft diameter matches the gearbox bore. The gearbox slides onto the shaft, and a keyway or a shrink disc clamps it in place. Total assembly length is minimized: no coupling hub, no spacer, no shaft stub protruding from the gearbox. The driven shaft runs continuously through the gearbox, giving the output bearing excellent shaft support and good moment load capacity.<\/p>\n

The critical requirement for hollow shaft designs: the gearbox housing cannot rotate freely on the shaft. A torque arm or anti-rotation bracket must connect the gearbox housing to the machine frame, reacting the output torque without constraining the gearbox axially (since the shaft and housing may have slight relative movement under thermal expansion). This torque arm must be designed for the full output torque with an appropriate safety factor. A missing or undersized torque arm is a failure mode that shows up as the gearbox housing slowly rotating on the shaft under repeated load cycles\u2014sometimes causing a cable failure or a sensor damage before anyone notices the rotation.<\/p>\n

Hollow shaft gearboxes are well-suited to: conveyor tail and head shaft drives where the gearbox mounts directly to the conveyor shaft; roller drive systems; fan and blower shaft drives; and any application where eliminating the coupling between gearbox and driven shaft simplifies the installation and reduces total drivetrain backlash.<\/p>\n

\"\"<\/p>\n

Concentricity and Its Effect on Performance<\/h2>\n

Whatever output configuration is selected, concentricity between the gearbox output and the driven component matters\u2014particularly at high speed or in precision applications.<\/p>\n

With a keyed shaft output, concentricity depends on the quality of the coupling and how carefully it’s aligned. A rigid coupling with good precision between bore and OD transfers the gearbox output shaft runout directly to the driven component. A flexible coupling accommodates some eccentricity but introduces its own angular play. For high-speed drives, even small runout at the shaft output creates vibration that compounds through the drivetrain.<\/p>\n

With an output flange, the pilot diameter controls concentricity. The driven component’s bore fits over the pilot spigot, centering it automatically. For precision applications, the pilot diameter tolerance and the driven component bore tolerance determine the concentricity achievable\u2014typically within a few hundredths of a millimeter for precision-machined components on a ground pilot diameter.<\/p>\n

With a hollow shaft, the bore diameter and the driven shaft diameter determine concentricity. A precision-ground bore on a precision-ground shaft achieves excellent concentricity without any alignment procedure.<\/p>\n

\"\"<\/p>\n

Making the Decision: A Practical Framework<\/h2>\n

Work through these questions in order:<\/p>\n

    \n
  1. What is the driven component?<\/strong> If it’s a standard off-the-shelf component\u2014sprocket, pulley, coupling\u2014keyed shaft is almost always simplest. If it’s a custom machine component or a rotary table that can be designed to interface directly, flange output is worth specifying. If the gearbox mounts directly onto a driven shaft, consider hollow shaft.<\/li>\n
  2. What are the moment load requirements?<\/strong> If the driven component applies significant bending loads to the gearbox output\u2014a long overhang, a heavy cantilevered mass\u2014flange or hollow shaft output handles this better than a keyed shaft. Calculate the actual moment load and compare it to the rated values in the datasheet for each configuration.<\/li>\n
  3. Is total assembly length critical?<\/strong> Hollow shaft gives the shortest assembly. Output flange is next. Keyed shaft with coupling is typically longest. If the installation envelope is the binding constraint, start with hollow shaft or flange output and work backwards.<\/li>\n
  4. Is precision positioning critical?<\/strong> Flange and hollow shaft outputs eliminate coupling play from the drivetrain. If total system backlash must be minimized, removing the output coupling is a meaningful step\u2014and flange or hollow shaft outputs achieve this without adding cost to the gearbox itself.<\/li>\n
  5. Is there a torque arm mounting point available?<\/strong> Hollow shaft requires one. If the machine frame doesn’t have a suitable torque arm attachment point, hollow shaft adds a design task. Keyed shaft and flange outputs don’t require this.<\/li>\n<\/ol>\n

    \"\"<\/p>\n

    Frequently Asked Questions<\/h2>\n

    Can I convert a keyed shaft output to a flange output after purchase?<\/h3>\n

    No \u2014 these are separate manufacturing configurations, not field-modifiable options. The housing geometry and bearing arrangement differ between configurations. If the wrong output type was ordered, a new gearbox with the correct configuration is required.<\/p>\n

    What is the pilot diameter on an output flange used for?<\/h3>\n

    The pilot diameter (also called the spigot) is a precision-machined cylindrical protrusion on the output flange face. The driven component’s bore fits over this pilot, centering it concentrically with the gearbox output axis. This self-centering feature eliminates the manual alignment step required with shaft outputs and achieves concentricity limited only by the dimensional tolerances of the pilot and the mating bore.<\/p>\n

    How do I size the torque arm for a hollow shaft gearbox?<\/h3>\n

    The torque arm must react the full output torque of the gearbox. The force at the torque arm attachment point equals the output torque divided by the effective arm length (distance from the gearbox shaft center to the attachment point). Size the bracket and fasteners for this force with a safety factor appropriate to the application\u2014typically 2.0 or higher for industrial service. The arm must allow free axial movement of the gearbox on the shaft to accommodate thermal expansion; a slotted attachment or spherical joint at one end is typical.<\/p>\n

    Does output configuration affect backlash?<\/h3>\n

    The gearbox’s internal backlash is the same regardless of output configuration. What changes is whether the output interface adds backlash to the total system. A keyed shaft with a coupling adds coupling clearance. A flange output bolted directly to the driven component adds none. A hollow shaft with a keyway adds keyway clearance; with a shrink disc, it adds essentially none. For the lowest total system backlash, flange or hollow shaft with a shrink disc is preferable to keyed shaft with a coupling.<\/p>\n

    Is flange output stronger than shaft output?<\/h3>\n

    For moment loads specifically, yes. A flange distributes the bending moment across a bolt circle and a large diameter housing face, which is inherently stiffer than a cantilevered shaft extension. For pure torsional torque transmission, both configurations are adequate\u2014the gear train transmits the torque, not the output shaft geometry. The advantage of flange output is specifically in moment load handling and concentricity control.<\/p>\n

    What shaft diameters are available for hollow shaft right angle planetary gearboxes?<\/h3>\n

    Available bore diameters are specific to each frame size and product line. Common bore ranges in servo-grade hollow shaft gearboxes run from approximately 14 mm in small frames to 80 mm or more in large frames. For replacement or new design projects, confirm the available bore diameter against your driven shaft diameter before specifying a hollow shaft unit.<\/p>\n

    \"\"<\/p>\n

    Specifying the Right Output Configuration<\/h2>\n

    The output configuration of a right angle planetary gearbox<\/a> should follow from what the application actually requires\u2014not from a default preference for shaft output. Getting this decision right at the design stage avoids costly changes and makes the installation simpler, more precise, and more reliable.<\/p>\n

    EPG Canada Sales Representative Co., Ltd<\/strong> provides gearbox selection support for Canadian OEMs and machine builders across North America. If you need help deciding between shaft, flange, or hollow shaft output for your application, or confirming dimensional compatibility with your driven component, send the details.<\/p>\n

    Email:<\/strong> sales@metalite.net<\/a>
    \nPhone:<\/strong>     +1-604 719 2870<\/a>
    \nAddress:<\/strong> 10891 Hogarth Dr, Richmond, BC V7E 3Z9, Canada<\/p>\n

    When contacting us about output configuration, include: driven component type and interface dimensions; output torque and any radial or moment loads; assembly length constraints; precision requirements (backlash at the output interface); and torque arm mounting options if hollow shaft is being considered. See the full planetary gearbox range<\/a>, the right angle planetary gearbox series<\/a>, or contact us directly<\/a>.<\/p>\n<\/div>","protected":false},"excerpt":{"rendered":"

    Right Angle Planetary Gearbox: Output Shaft vs Flange Output Output configuration is one of those specification decisions that gets made once and can’t easily be undone. Keyed shaft, output flange, hollow shaft\u2014these are manufacturing choices, not field-adjustable settings. Order the wrong one and you’re looking at a new unit, a custom adapter, or a machine […]<\/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":[50],"tags":[94,95,93],"class_list":["post-1667","post","type-post","status-publish","format-standard","hentry","category-planetary-gearbox-blogs","tag-flange-output-gearbox","tag-hollow-shaft-planetary-gearbox","tag-planetary-gearbox-output-shaft"],"_links":{"self":[{"href":"https:\/\/metalite.net\/de_at\/wp-json\/wp\/v2\/posts\/1667","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/metalite.net\/de_at\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/metalite.net\/de_at\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/metalite.net\/de_at\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/metalite.net\/de_at\/wp-json\/wp\/v2\/comments?post=1667"}],"version-history":[{"count":3,"href":"https:\/\/metalite.net\/de_at\/wp-json\/wp\/v2\/posts\/1667\/revisions"}],"predecessor-version":[{"id":1678,"href":"https:\/\/metalite.net\/de_at\/wp-json\/wp\/v2\/posts\/1667\/revisions\/1678"}],"wp:attachment":[{"href":"https:\/\/metalite.net\/de_at\/wp-json\/wp\/v2\/media?parent=1667"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/metalite.net\/de_at\/wp-json\/wp\/v2\/categories?post=1667"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/metalite.net\/de_at\/wp-json\/wp\/v2\/tags?post=1667"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}