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Can a finished gear be modified with secondary machining?A finished gear may accept secondary machining, but suitability depends on its material, hardened regions, remaining wall thickness and accuracy requirements. Bore enlargement, keyways, tapped holes or hub changes need a part-specific review. PairGears lists custom bore and shaft features; confirm whether an existing part can be modified or a new gear should be manufactured with those features.Mark the exact features to be changedProvide the existing part drawing and a marked final drawing. Identify the bore, keyway, holes, hub faces or shaft features to be changed, with dimensions, tolerances and the datum relationship to the teeth.For example, enlarging a bore also reduces the material between the bore, keyway and tooth root. Feasibility therefore depends on the final section and torque path, not only whether a boring tool fits. Changes to a hub or locating face can affect axial position, retention and runout.Bores, holes and locating faces must be assessed together with the remaining gear section. Image: PairGears.Check the hardness map before choosing a processA gear with hardened teeth and a machinable hub differs from a part hardened throughout or case-hardened over the surfaces to be altered. Obtain the material and heat-treatment record, then identify the local hardness and any required case depth.Do not assume ordinary drilling, tapping or broaching is suitable for a hardened area. A specialist machining route may be possible, but removing a required hardened layer, damaging a tooth root or introducing heat damage can make the result unacceptable. The machining plan must preserve the final drawing requirements.The location and extent of hardening affect which later operations are feasible. Image: PairGears.Agree the final inspection and the new-part alternativeDefine how the part will be located and clamped without damaging its teeth. After machining, verify the changed dimensions, bore-to-tooth runout, relevant locating faces, burr removal and any affected surface or hardness requirements. Record the final condition and drawing revision.If adequate material, machinability or datum control is missing, request a new part with the features included in its planned manufacturing route. Review the PairGears custom cylindrical gear and shaft capabilities and obtain part-specific feasibility confirmation before proceeding.A newly planned manufacturing route may be preferable when a finished part cannot be modified to specification. Image: PairGears.Related questionsCan I order a gear with a smaller bore than the catalog size?How do I verify gear concentricity and runout when the gear mounts on a shaft?

How are module, pressure angle and helix angle confirmed from an incomplete drawing?Confirm missing tooth data by combining measurements of the gear with its mating-part and assembly information. Tooth count and outside diameter provide an initial check, but do not uniquely establish module, pressure angle or profile shift. For helical gears, also determine hand and distinguish normal from transverse values. Record the reconstructed geometry and unresolved assumptions for approval before manufacture.Start with observations, not assumed catalog valuesCount the teeth and record outside diameter, face width, bore or shaft interfaces, visible wear and tooth hand. Supply any legible drawing dimensions, part markings, mating gear and measured center distance.For a standard, unshifted external spur gear with full-depth teeth, the relation m = da / (z + 2) gives a useful preliminary module check. A 30-tooth gear with a 64 mm outside diameter suggests module 2 under those assumptions. A shifted, worn or specially modified gear may not follow that shortcut.Initial dimensional checks support identification; caliper measurements alone do not establish the tooth system. Image: PairGears.Reconstruct a consistent tooth geometryUse suitable tooth-profile and lead measurements, supported where appropriate by span or over-pin measurements, to evaluate candidate geometry. Check the full set of results rather than selecting a familiar pressure angle from appearance.Different nominal parameter combinations can describe the same measured base diameter or lead. Manufacturing deviations, wear and flank modifications also affect the reconstruction. For helical teeth, identify whether the reported module and pressure angle are normal or transverse, and state the helix angle at its defined reference cylinder.Turn observations into a documented geometry definition with explicit assumptions. Image: PairGears.Approve the replacement definition with the mating assemblyRecord which values were measured, inferred or supplied by the customer. Review the candidate geometry against the mating gear, center distance, required ratio, backlash and contact conditions. Where uncertainty remains, agree a sample and assembly check before releasing production.The PairGears custom gear drawing checklist helps organize the final requirements. Reconstructing tooth geometry does not by itself establish material, heat treatment, load capacity or the original designer's intent.A reconstructed drawing needs review and sample verification before production release. Illustration: PairGears.Related questionsCan I request measurement of other manufacturer’s gear products?What information is needed for a gear calculation?

How can I distinguish gear backlash from shaft or bearing play?Separate the direction and location of the movement. Gear backlash is relative rotation between mating tooth flanks when one member is restrained. Shaft or bearing play involves radial or axial movement, while a loose hub can add rotation between the gear and shaft. A single rocking test can combine these effects, so measure them separately before adjusting the mesh.Measure rotational clearance across the tooth meshWith the machine safely stopped and isolated, restrain one member and gently reverse the other using the agreed measuring load. Record where the indicator contacts the gear, its orientation, the assembly position and temperature. Check several rotational positions instead of judging the mesh from one tight or loose spot.A tangential indicator reading depends on its measuring radius; it is not automatically the circular backlash at the reference circle. Also watch for shaft movement during the test. In the diagram, radial backlash is a gear-geometry term related to center-distance change; it is not bearing radial clearance.Backlash definitions refer to the tooth mesh. The radial-backlash label does not describe looseness in a bearing. Diagram: KHK Gears.Measure shaft movement independentlyUse a stable reference on the housing to measure radial shaft movement and axial endplay separately, following the equipment or bearing maker's procedure. Observe whether the shaft moves relative to the bearing, a bearing ring moves in its seat, or the housing itself deflects. A reading at a remote shaft end can include bending as well as clearances.Some bearing arrangements intentionally use operating clearance, preload or axial freedom. Compare results with the specified arrangement and condition; there is no universal acceptable amount of hand-felt play. Increasing bearing preload solely to hide gear rocking can create a different problem.Bearing internal clearance describes relative movement of the rings in defined directions. Diagram: JTEKT.Check the hub connection before changing the gearsIf the gear rocks relative to its own shaft, inspect the key, spline, clamp or other specified connection. For example, a restrained mating gear and a visibly moving hub-to-shaft joint indicate that the observed lost motion includes that joint; reducing tooth clearance will not repair it.Record the separate measurements and inspect the locating faces, retention and mounting condition before deciding on repair. Restore the specified connection and bearing arrangement, then recheck mesh backlash, contact and runout. The PairGears inspection-report guide can help organize the gear evidence; a loose-part gear report alone cannot establish the condition of the assembled bearings and housing.Identify which joint moves: the gear-to-shaft connection and the shaft supports are different parts of the assembly. Image: PairGears.Related questionsWhat tolerances should I specify to control gear backlash and repeatability?How do I verify gear concentricity and runout when the gear mounts on a shaft?

How do I choose spur gear tooth counts for a required ratio?For one external spur gear pair, define the reduction ratio as input speed divided by output speed, then choose integer tooth counts satisfying i = z2/z1. The ratio alone leaves many possible pairs. Use the available center distance and module to narrow the choice, then check tooth geometry, strength, contact, mounting and the permitted ratio error.State which gear drives and how exact the ratio must beLet z1 be the input pinion tooth count and z2 the driven gear tooth count. Using positive speed magnitudes, i = n1/n2 = z2/z1. An external pair reverses rotation direction. For a 3:1 reduction, 20/60 and 24/72 teeth give the same nominal ratio but different sizes at the same module.Specify whether the target is exact or has an allowed error. For an approximate candidate, calculate the actual ratio from its integer tooth counts and compare it with that allowed range. Rounding a calculated tooth count without recalculating the ratio changes the design.The ratio follows the tooth counts of the driving and driven members. This schematic is not the numerical example below. Diagram: KHK Gears.Combine the ratio with the center-distance constraintFor an unshifted standard external spur pair at its reference center distance, a = m(z1 + z2)/2. Therefore z1 = 2a/[m(1 + i)] and z2 = i × z1. Here a and module m use consistent length units. These equations do not replace the working-center-distance calculation for a profile-shifted pair.Example: with m = 2 mm, a = 80 mm and i = 3, the sum is 80 teeth, giving z1 = 20 and z2 = 60. If a is instead 75 mm, the same assumptions give 18.75 and 56.25 teeth, so no exact integer solution exists under all three constraints. Review module, center distance, permitted ratio error or a properly calculated alternative geometry.Housing space and shaft positions constrain a tooth-count choice. The pictured gearbox is application context, not the 20/60 spur-pair example. Image: PairGears.Validate the candidate before releasing the drawingCheck undercut and interference, contact ratio, tooth-root and surface capacity, face width, material, lubrication and the duty cycle. Verify the bore and hub space as well as the outside diameters. Profile shift can alter geometry and working center distance; it does not change the ratio of a fixed pair of tooth counts.The 20/60 calculation establishes geometry only, not a load rating. Submit the candidate pair with torque, speed, life and accuracy requirements. The PairGears gear drawing checklist helps carry the chosen tooth counts and their operating requirements into manufacturing review.The selected geometry also needs a suitable manufacturing and inspection route. Image: PairGears.Related questionsWhy are spur gear ratios not always whole numbers?How are gears designed?

How should a plastic gear be fastened to a shaft?Fasten a plastic gear using a connection designed for its resin, hub geometry and duty. A key, shaped bore or engineered metal hub may be suitable, but a mounting method used on a steel gear is not automatically suitable for plastic. Check torque transfer, local stress, temperature, moisture effects and axial retention before approving the assembly.Start with the actual gear and bore designIdentify the manufacturer, part drawing, resin grade and whether the hub is entirely plastic or contains a metal insert. A bore diameter alone does not identify the permitted mounting method. For a purchased molded gear, follow the mounting instructions for that exact part before adding a keyway, cross-hole or set screw.A shaped bore can provide a defined torque path, while a round bore needs another specified connection. Treat the shaft fit and axial location as drawing requirements rather than relying on the teeth to keep the gear in position.Packaged molded gears illustrate a manufacturing route, not a universal shaft-fit specification. Image: KHK Gears.Check the plastic hub as well as the teethA keyway loads the sides of the plastic hub. Review its contact stress, effective length, corner radii and remaining material, especially with shocks or reversals. Where a plastic hub is unsuitable, an engineered metal hub can provide the shaft connection; its attachment to the plastic still needs its own capacity check.For example, a keyed metal insert introduces two interfaces: shaft-to-insert and insert-to-plastic. A satisfactory key calculation at the first interface does not prove that the second will resist slipping or loosening. Do not transfer steel interference-fit values directly to a plastic bore.Nylon stock for machined gears is distinct from an injection-molded part; identify the actual resin and construction. Image: KHK Gears.Specify the condition in which the fit is acceptedPlastic dimensions can change with temperature and moisture; the size of that change depends on the resin and condition. Specify the assembly temperature, material conditioning and operating environment. A room-temperature fit check alone may not describe the running condition.Define axial retention separately, then verify assembled runout and the connection under the agreed duty. Send both the gear and shaft drawings with peak torque, reversals, speed and environment. The PairGears custom cylindrical gear service provides a route for project review; the mounting design and manufacturing process must be agreed for the specific part.This MC901 example illustrates moisture sensitivity; its curve must not be applied to every plastic resin or molded gear. Diagram: KHK Gears.Related questionsWhat methods can fasten a gear to a shaft?Can PairGears make plastic gears from materials other than MC901 nylon?

Does downloadable gear CAD include manufacturing-ready tooth profiles?Not necessarily. Downloadable gear CAD may show an envelope or approximate tooth shape for assembly layout rather than the exact geometry needed for manufacturing. Check the provider’s stated purpose and request an approved tooth definition when production depends on it. File format alone does not establish accuracy, tolerances, root geometry or the intended mating conditions.Confirm what the model is intended to representAn assembly model may be sufficient to check overall space, shaft positions and mounting interfaces while simplifying the teeth. Do not infer machining suitability from a smooth-looking solid or the presence of individual teeth. Read the model’s limitations and ask the supplier which features are controlled.An involute flank has a defined geometric construction, illustrated here. A faceted outline or a visually similar curve is not automatically that construction within a specified tolerance. Request tooth-profile data separately if it is not included in the supplied CAD package.The intended flank geometry must be defined and controlled; visual resemblance is insufficient. Diagram: KHK Gears, Figure 3.3.Keep the tooth definition with the approved drawingProvide tooth count, module or diametral pitch, pressure angle, profile shift where applicable and the required tooth thickness or backlash basis. Define tip and root geometry, face width, any modifications, datums and accuracy requirements. Include the mating gear and operating center distance.The PairGears custom gear drawing checklist helps organize this information. Agree whether the drawing, a controlled 3D model or a specified combination governs manufacture, and resolve any conflict before release. A STEP, DXF or STL extension by itself does not settle that question.A basic rack profile illustrates distinct tooth-system parameters; it is not a finished gear production model. Diagram: KHK Gears, Figure 3.1.Verify imported geometry and the finished tooth formFor example, when using a downloaded model as the starting point for a replacement, first confirm units, scale, model revision and whether the tooth flanks and roots are exact, approximated or omitted. Do not silently convert a layout model into the manufacturing master.Have the supplier confirm the production data and inspection method. Finished-part profile, lead and pitch measurements should be evaluated against the approved specification, rather than against the model’s appearance. PairGears CAD deliverables and any exact tooth data should be agreed for the specific project; a general downloadable model is not a blanket accuracy guarantee.Inspection compares the manufactured tooth form with its specification. This sample report does not define the tolerances for a new order. Image: PairGears.Related questionsWhat data is needed to make a custom spur gear?Can you provide tooth profile/lead charts and explain what “pass/fail” looks like?

Can I order a gear with a smaller bore than the catalog size?A smaller bore can be specified on a new custom gear, subject to manufacturing review. PairGears lists customized bores and shaft features among its capabilities. An existing finished bore cannot be made smaller by removing more material. Request a new part with the required bore, or have an engineered sleeve arrangement reviewed for the application.Distinguish a new bore specification from reworkThe PairGears custom cylindrical gear service lists bores, keyways and other shaft features made to requirements. Supply the exact finished bore diameter and tolerance for feasibility review; a general customization listing does not establish every available size or fit.For example, if an existing gear has a 25 mm bore and the shaft is 20 mm, further boring or reaming will not close the gap. The practical choices are a newly manufactured gear with the specified interface or a separately designed adaptation. These dimensions are an example, not a catalog listing.A finished bore is a functional shaft interface, not just an opening in the gear. Image: PairGears.Define how the smaller shaft will transmit torqueState shaft size and tolerance, bore fit, torque, speed, load cycle, axial location and any key, spline or clamp arrangement. Confirm the mating gear data so that changing the shaft interface does not accidentally change the tooth specification.If a sleeve is proposed, review the gear-to-sleeve and sleeve-to-shaft interfaces separately. The design must address torque transfer, axial retention, runout, wall thickness and operating conditions. A sleeve chosen only by nominal diameters is not a verified mounting solution. Obtain an approved assembly drawing before manufacture.Agree the required bore, shaft-interface and tooth checks in the inspection documents. Image: PairGears.Check the finished fit after the manufacturing route is setSpecify the locating face and bore datum, required dimensional checks and the relationship between the finished bore and gear teeth. Agree when heat treatment and finishing occur, and verify fit and runout in the final delivery condition.Request a dimensional report for the relevant interface. A hardness or metallographic report provides different evidence and does not confirm bore size or shaft fit. The PairGears inspection-report guide helps separate those checks. Confirm the proposed route and acceptance criteria before ordering.Illustrative material-condition report; its results do not verify bore dimensions or fit and are not specifications for this order. Image: PairGears.Related questionsCan a gear be made without a bore?How do I verify gear concentricity and runout when the gear mounts on a shaft?

Do mating spiral bevel gears need opposite spiral hands?Yes. A conventional external spiral bevel gear pair combines a right-hand member with a left-hand member. Opposite hands are necessary, but they do not establish compatibility by themselves. The two gears must also share the intended mating geometry, ratio and shaft arrangement. Specify both members as a pair rather than selecting a replacement by spiral hand alone.Separate spiral hand from tooth-trace formSpiral hand describes the direction of tooth curvature. Using the convention described by KHK, look from the small end: clockwise tooth curvature is right-hand and counterclockwise curvature is left-hand. Record the viewing convention on the drawing if a photograph could be ambiguous.Tooth-trace form is a separate detail. The illustration shows different curved tooth arrangements; a similar-looking curve or the opposite hand does not identify a compatible mate. The PairGears spiral bevel gear guide provides further design context.Different curved tooth arrangements illustrate why spiral hand alone is not a complete specification. Diagram: KHK Gears.Identify the intended pinion and gear togetherSend both drawings or the original matched-set references. Include tooth counts, tooth-size and pressure-angle conventions, shaft angle, spiral angles and hands, face widths, mounting distances and shaft interfaces. Identify the gear system and any specified profile or contact corrections.For example, a right-hand 20-tooth pinion does not become compatible with every left-hand 40-tooth gear. Those counts suggest a 2:1 ratio, but the remaining geometry and mounting requirements still need to match. PairGears lists drawing-based options in its custom bevel gear service.Illustrative contact check on a bevel pair; the pictured straight teeth do not demonstrate spiral hand. Image: KHK Gears.Verify contact and loading before accepting a replacementCheck the assembled contact pattern and backlash at the specified mounting positions. Keep any required matched-set identification with the parts, and obtain supplier confirmation before combining a new member with an existing one.Rotation direction is another specification: reversing rotation does not change a gear’s manufactured spiral hand, but it changes the loaded flank and can affect bearing thrust. Give the supplier both drive directions and the duty cycle when relevant. Opposite hands alone do not prove acceptable contact, quiet operation or load capacity.A contact-pattern check evaluates the assembled pair; it does not replace the mating-geometry specification. Diagram: KHK Gears.Related questionsCan a spiral bevel gear set run in both directions?Can PairGears make bevel gears for shaft angles other than 90 degrees?

What does a JIS Type 3 worm tooth profile mean?JIS Type 3 describes a worm tooth-profile form produced with a milling cutter or grinding wheel that has a trapezoidal profile in the tool plane. It is also called the K form in the classification described by KHK. Type 3 identifies the profile family; it does not mean accuracy grade 3 or a three-start worm.Read Type 3 as a tooth-form designationThe defining trapezoidal shape belongs to the cutter or grinding wheel in its tool plane. Do not interpret that description as a requirement for a straight-sided trapezoid in every section through the finished worm.On a drawing, keep tooth form, accuracy standard and number of starts in separate fields. For example, “Type 3” and “two starts” can describe the same worm without contradiction: one identifies the profile family and the other counts the helical threads. Confirm the exact standard and edition required by the drawing.Tool arrangement for a Type III worm. Diagram: KHK Gears, Figure 4.15.Specify the remaining worm geometryA profile designation alone leaves the size and mesh undefined. State the module and its axial or normal convention, pressure angle and its convention, number of starts, reference diameter, lead or lead angle, hand, face length and shaft details. Supply the wheel data and intended center distance with the worm drawing.The adjacent diagram distinguishes normal and axial quantities. Values in those two planes are not interchangeable without the correct conversion. The PairGears worm gear manufacturing guide provides further context for a paired manufacturing specification.Axial and normal sections use different geometric quantities. Diagram: KHK Gears, Figure 4.16.Match the wheel and the inspection requirementHave the supplier verify that the wheel’s generated tooth geometry matches the specified worm, with the intended mounting dimensions and backlash. Matching a nominal module and tooth counts alone does not establish a compatible replacement set.Envelope geometry is another separate design choice, illustrated here. Neither a tooth-form label nor an envelope description guarantees efficiency, self-locking or load capacity. For a replacement, send both drawings or identify the existing matched set, and agree how profile, dimensions and functional contact will be checked.Envelope geometry is a separate specification from the Type 3 tooth-profile designation. Image: PairGears.Related questionsWhat is the difference between single-start and double-start worms?What assembly errors are allowable for a worm gear pair?

Can PairGears make plastic gears from materials other than MC901 nylon?Yes. PairGears lists POM, PA6/PA66, PBT, PEEK and PPS among its custom plastic gear material options. Specify the exact polymer grade and service conditions for review. Changing from MC901 nylon is a material and gear-design decision: confirm dimensional behavior, tooth loading, wear and the manufacturing process before approving a replacement.Choose a grade, not only a polymer nameThe PairGears custom plastic gear page lists these alternatives for technical review. POM is commonly considered where low moisture uptake and dimensional stability matter. Nylon selection should account for moisture conditioning. PEEK and PPS may be candidates for more demanding thermal or chemical environments, depending on grade and application.Specify the manufacturer’s grade designation, any fillers or lubricating additives, and the required material documentation. A family name such as “nylon” or “PEEK” does not define every property needed for a gear calculation.The polymer grade and machining route must suit the approved gear design. Image: PairGears.Review dimensions when substituting a materialProvide torque, speed, duty cycle, temperature, humidity, chemical exposure, lubrication and mating-gear details. Have the designer review creep, thermal expansion, moisture-related dimensional change and tooth strength using data for the chosen grade.For example, a nylon replacement that fits a shaft during a dry room-temperature inspection may behave differently in warm, humid service. Specify the measurement condition and required running clearance. Do not assume that copying the old drawing into another resin preserves backlash or service life.Machining and injection molding require different process and dimensional reviews. Image: PairGears.Agree the process and sample checksPairGears lists CNC machining and injection molding as possible routes, selected for geometry, quantity and feasibility. Confirm the chosen route, tooling requirements and sample acceptance criteria in the quotation.Check tooth geometry, bore fit, runout and the functional mesh under agreed conditions. If the application has a life or noise target, define a representative test rather than inferring performance from the resin name. A sample approval should identify its material grade and drawing revision so repeat orders use the same specification.Verify critical dimensions and functional fit on the specified material and sample. Image: PairGears.Related questionsHow is the surface durability of plastic gears assessed?Can gears be used in high-temperature environments?

Can PairGears make bevel gears for shaft angles other than 90 degrees?Yes. PairGears lists custom shaft angles for bevel gears, subject to review of the complete gear pair and assembly requirements. Send the required angle, ratio, mounting dimensions and operating conditions with your drawings. A standard 90-degree pair cannot simply be installed at another angle; the mating geometry must be designed for the intended arrangement.Specify the angle between the shaft axesFor an intersecting-axis bevel drive, show the included shaft angle on the assembly drawing. Keep it separate from each gear’s pitch-cone angle and, for spiral bevel gears, the spiral angle. The PairGears custom bevel gear service lists shaft angles customized to assembly requirements.For example, an equal-ratio pair designed for a 60-degree shaft angle has nominal pitch-cone angles of 30 degrees each. That geometry differs from an equal-ratio 90-degree pair. This example describes geometry, not an available stock size or a confirmed production limit.Illustrative bevel-gear machining; the image does not identify a particular shaft angle. Image: PairGears.Request the two gears as a matched designProvide both tooth counts or the required ratio, the stated tooth-size system, pressure angle, tooth form and face widths. Include mounting distances, shaft intersection, bearing locations, bores or shaft connections and the available housing space. Where applicable, state spiral hands and the required direction of rotation.A replacement order should identify the existing mating gear and its drawing revision. Matching outside diameter alone does not establish compatibility. If either axis is offset rather than intersecting, show that explicitly: it changes the type of gear geometry the supplier must evaluate.Finishing and inspection requirements belong in the custom pair specification. Image: PairGears.Confirm feasibility and assembly acceptanceSend torque, speed, duty cycle, lubrication and quantity so the supplier can review the design and manufacturing route. Agree material, heat treatment, dimensional tolerances and the required contact-pattern or running checks before ordering.For a new non-90-degree assembly, require confirmation against the submitted drawings rather than treating a general customization listing as a guarantee. Contact pattern and backlash should be checked at the specified mounting positions; moving a standard pair to a different shaft angle is not a substitute for a compatible design.A paired finishing setup illustrates why both mating members and their mounting conditions matter. Image: PairGears.Related questionsWhat is the shaft angle in a gear pair?What is a miter gear?

Which Mercedes-Benz truck gearbox parts does PairGears list?PairGears lists input shafts, intermediate shafts and transmission gears for specified Mercedes-Benz truck gearbox applications. Examples include input-shaft reference 1268302001 and intermediate-shaft reference 3662640105. Use each listing as a starting point for identification, then confirm the transmission model, variant and part details. A truck brand or photograph alone is insufficient to establish replacement compatibility.Start with a specific catalog referenceThe catalog lists input shaft 1268302001 for AK6-90 and S6-90 applications, and intermediate shaft 3662640105 for AK6-80 and S6-80 applications. These are the application labels on the individual PairGears listings.The 0073301465 double-gear listing also gives Mercedes-Benz and ZF reference information. Catalog cross-references help identify a candidate; they do not establish interchangeability across all gearbox versions or identify the item as a genuine vehicle-manufacturer part.Illustrative Mercedes-Benz truck; no gearbox or parts compatibility is implied. Photo: gaspar zaldo / Unsplash.Distinguish the component and its mounting detailsAn input shaft receives drive from the clutch side, while an intermediate shaft supports another part of the transmission’s gear path. Their names do not specify a common interchangeable geometry. Identify the exact component position in the transmission parts diagram.For a shaft, compare overall length, bearing journals, splines, grooves and integral gear details. For a separate gear, compare tooth count, tooth geometry, bore or spline and engagement features. A matching external appearance does not resolve differences hidden inside the assembly.Generic input-shaft features to compare with the specified replacement; not a Mercedes-Benz fitment drawing. Image: PairGears.Send identification details before requesting a quoteProvide the transmission identification-plate information, vehicle details, existing part number and any superseding reference supported by the parts documentation. Add clear photographs and a dimensioned drawing or measurements if the number is missing or unreadable.For example, a request for “an S6 gearbox shaft” remains incomplete without its exact model, variant and shaft reference. Have the supplier confirm the matched listing, specification, quantity and current availability. Where a custom replacement is proposed, agree material, heat treatment and inspection requirements before production.Gearbox internals illustrate why the complete mating and mounting arrangement matters. Image: PairGears.Related questionsHow many gears are in a truck transmission?What do gears 1, 2, 3, 4 and 5 mean in a manual transmission?

How do I specify profile shift for crossed-helical screw gears?Specify profile shift as part of the complete crossed-helical gear-pair design, with a stated coefficient convention for each member. Provide normal module, normal pressure angle, tooth counts, helix angles and hands, shaft angle and operating center distance. A designer must check the resulting working geometry and tooth contact. Moving an existing gear along its shaft does not create profile shift.Separate tooth modification from assembly movementIn this context, screw gears are crossed-helical gears operating on nonparallel, nonintersecting shafts. Profile shift describes a change in generated tooth geometry relative to the reference tooth system. It is specified during design and manufacture.If “shifting” means repositioning a finished gear on its shaft, describe that as an axial mounting adjustment. It does not change the gear’s manufactured profile-shift coefficient. Keeping the two meanings separate helps the supplier interpret the drawing correctly.Shaft angle and helix hands belong to the pair specification. Diagram: KHK Gears, Figure 4.14.Submit the pair geometry and the design objectiveGive the normal module and pressure angle common to the tooth system, each tooth count, reference helix angle and hand, required shaft angle, center distance, face widths and available envelope. State whether coefficients use a normal-system convention; do not mix normal and transverse data.For example, if a replacement must fit an existing housing, provide its measured center distance and shaft angle together with both gears’ drawings. Ask for a compatible pair calculation instead of selecting one gear’s shift coefficient in isolation. The PairGears custom gear drawing checklist helps organize the required drawing information.Specify the tooth system and coefficient convention explicitly; this drawing is illustrative. Image: PairGears.Recalculate the mesh before releasing the drawingA shifted crossed-helical pair needs a check of its working pitch diameters and working helix angles. Do not automatically substitute the reference helix angles into a shaft-angle relationship derived for an unshifted pair. The helix-hand arrangement also matters.Check tooth thickness, tip and root clearance, interference, backlash and contact at the intended mounting dimensions. Evaluate load, speed, lubrication and bearing thrust separately. Crossed-helical contact and sliding limit the application; a geometrically possible profile shift alone does not establish adequate life or load capacity.Verify the finished tooth geometry against the approved pair calculation. Image: PairGears.Related questionsDoes profile shift change a gear’s reference diameter?How can I reduce wear in crossed-helical screw gears?

Can PairGears manufacture custom double-helical gears?Yes. PairGears lists custom double-helical and herringbone gear services. Send the complete gear and mating-part drawings for manufacturing review, including tooth geometry, material, heat treatment and inspection requirements. Confirm whether the design has a center relief gap or continuous V-shaped teeth; the required manufacturing route and acceptance criteria depend on that distinction.Identify the exact tooth arrangementDouble-helical designs combine left-hand and right-hand teeth. A center relief gap separates the two halves in many designs; herringbone commonly describes teeth meeting in a continuous V. Terminology varies, so the drawing should show the intended arrangement explicitly.The PairGears comparison of helical gear types explains these differences. Opposing tooth forces can balance axial thrust under balanced loading, but alignment, load sharing and bearing requirements still need an engineering check.A historical herringbone arrangement illustrates opposing tooth directions; this is not a PairGears product sample. Photo: Parchaco / Wikimedia Commons, CC0.Provide a complete manufacturing specificationInclude tooth count, module and its normal or transverse convention, pressure angle, helix angle, both tooth hands, face widths and center-gap dimensions. Specify the bore or shaft connection, datums, material, heat treatment, tolerances and inspection standard. Supply mating-gear geometry and the intended operating center distance.For example, a replacement request describing only “a double-helical gear with the same outside diameter” leaves tooth compatibility and mounting unresolved. Add the original drawing revision, application speed and torque, and photographs or measurements of the existing assembly. PairGears describes custom options in its custom helical gear service guide.Review the drawing and application together before confirming the manufacturing route. Image: PairGears.Agree how the two halves will be checkedAsk the supplier to confirm machining access, the relative tooth alignment between halves, required finishing operations and the inspection plan. A narrow gap or continuous V may constrain tool access differently from a separated arrangement.Agree the dimensional report and any paired contact or running checks before ordering. The available process, achievable tolerances, price and delivery schedule must be confirmed for the submitted design; a general service listing does not establish those values for every gear.Illustrative helical-gear inspection; a double-helical part needs an agreed check of both halves. Image: PairGears.Related questionsWhat are the advantages of helical gears?How do you calculate axial thrust in a helical gear?