{"id":1780,"date":"2026-04-07T09:01:08","date_gmt":"2026-04-07T09:01:08","guid":{"rendered":"https:\/\/wormwheelgear.top\/?post_type=product&p=1780"},"modified":"2026-04-07T09:01:08","modified_gmt":"2026-04-07T09:01:08","slug":"duplex-worm-gear-dual-lead-continuously-adjustable-backlash","status":"publish","type":"product","link":"https:\/\/wormwheelgear.top\/sr\/product\/duplex-worm-gear-dual-lead-continuously-adjustable-backlash\/","title":{"rendered":"\u0414\u0443\u043f\u043b\u0435\u043a\u0441 \u043f\u0443\u0436\u043d\u0438 \u0437\u0443\u043f\u0447\u0430\u043d\u0438\u043a | \u0414\u0432\u043e\u0441\u0442\u0440\u0443\u043a\u0438 \u0432\u043e\u0434\u0438\u0447, \u043a\u043e\u043d\u0442\u0438\u043d\u0443\u0438\u0440\u0430\u043d\u043e \u043f\u043e\u0434\u0435\u0441\u0438\u0432\u0438 \u0437\u0430\u0437\u043e\u0440"},"content":{"rendered":"
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Every standard worm drive accumulates backlash as the tooth faces wear. The worn metal is gone \u2014 the center distance cannot be reduced, and the only way to close the gap between the worm thread flank and the wheel tooth face in a standard drive is to replace both the worm and the wheel. This is expensive and time-consuming, but for most industrial drives it is acceptable because the backlash specification is not critical. In precision positioning drives \u2014 CNC rotary tables, milling machine feed systems, measuring machine axes \u2014 even 0.05 mm of angular backlash is too much. A 0.05 mm backlash at the worm wheel pitch circle of a 100 mm diameter wheel translates to approximately 3.4 arc-minutes of positional error, enough to cause visible surface irregularities on a machined workpiece. Korea Ever-Power Worm Gear Co., Ltd manufactures duplex worm gear sets \u2014 also called dual-lead worm gears \u2014 that solve this problem by making the worm’s tooth thickness vary continuously along its length, so that axial shift of the worm restores the original backlash without replacing any components. This \u0434\u0443\u043f\u043b\u0435\u043a\u0441 \u043f\u0443\u0436\u043d\u0438 \u0437\u0443\u043f\u0447\u0430\u043d\u0438\u043a<\/a> set is the correct solution wherever bidirectional positioning accuracy must be maintained over the drive’s service life.<\/p>\n

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How the Dual-Lead Principle Works \u2014 The Engineering Mechanism<\/h2>\n

A duplex worm is manufactured with slightly different lead values on the left flank and the right flank of each thread. The difference is small but precisely controlled \u2014 typically a few tenths of a millimeter difference in axial pitch between the two flanks. The consequence of this difference is that the tooth thickness \u2014 measured at the pitch cylinder \u2014 increases continuously from one end of the worm to the other. At the thin end, the worm thread fits loosely in the wheel tooth gap with measurable backlash. At the thick end, the worm thread fits tightly with near-zero backlash. The gap between consecutive threads (the tooth space width) decreases correspondingly \u2014 the thread and gap are complementary.<\/p>\n

Backlash adjustment is made by shifting the worm axially so that the section of the worm with the needed tooth thickness comes into contact with the wheel, giving the desired backlash (Fig.1). This way, backlash can be adjusted to any desired value when mounting the gear. Even heavily worn gears can be readjusted delicately and continuously without modifying the tooth contact geometry or creating meshing interference \u2014 a key advantage over every alternative backlash control method.<\/p>\n

At the worm wheel, the different modules on each flank produce different addendum modification coefficients and different rolling circle diameters on the front side versus the rear side of each wheel tooth. Because of this asymmetry, the tooth profiles differ at the front and rear. However \u2014 and this is critical to understanding why duplex works \u2014 the thickness of each wheel tooth and the tooth gaps remain constant around the wheel circumference. This means the worm can shift to any axial position and the wheel tooth geometry is always correctly matched to the worm at that position. There is no “preferred” axial location with better contact than others \u2014 the contact quality is maintained uniformly across the full adjustment range.<\/p>\n

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Four Alternative Backlash Adjustment Methods \u2014 Why Each Falls Short<\/h2>\n

Before duplex worm gears became widely adopted, engineers used four other methods to control backlash in worm drives. Understanding what is wrong with each of these alternatives clarifies why duplex is the superior solution for precision positioning applications.<\/p>\n

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\n\n\n\n\n\n\n\n\n
Alternative Method<\/th>\nHow It Works<\/th>\nWhy It Is Problematic<\/th>\n<\/tr>\n<\/thead>\n
Eccentric hub center-distance variation<\/td>\nBoth the worm shaft and wheel shaft are mounted in an eccentric hub that rotates to change the center distance<\/td>\nMoving the center distance changes the contact pattern \u2014 the worm and wheel were designed for a specific center distance, and deviation shifts the contact zone toward the tooth tip or root, reducing the contact area and increasing tooth stress concentration. Efficiency deteriorates because the oil film geometry at the mesh is disrupted. Each adjustment causes significant start-up wear as the newly positioned contact zone beds in.<\/td>\n<\/tr>\n
Conical worm axial shift<\/td>\nThe worm is made with a slight taper \u2014 larger diameter at one end \u2014 and shifted axially to bring a different diameter section into contact with the wheel<\/td>\nA conical worm changes the effective pitch diameter as it shifts, changing the contact normal direction and the pressure angle at the mesh. This means the adjusted drive no longer operates at the design pressure angle \u2014 loading on the tooth flanks changes, and in severe cases the tooth geometry may produce edge contact. Manufacturing a correctly tapered worm with the required profile accuracy is also technically demanding.<\/td>\n<\/tr>\n
Split worm \u2014 two halves (Ott system)<\/td>\nThe worm is cut in two halves which are rotated or axially shifted relative to each other, causing the effective thread thickness to increase<\/td>\nSplitting the worm creates a geometric irregularity at the split plane \u2014 the thread profiles at the joint are not continuous. This irregularity shows up as a periodic noise event and vibration spike every time the split plane passes through the mesh. Alignment of the two halves at the split is critical and difficult to maintain under operational loads. The risk of improper assembly \u2014 one half rotated by an incorrect angle \u2014 causing immediate tooth damage is high.<\/td>\n<\/tr>\n
Split wheel \u2014 two disks<\/td>\nThe worm wheel is divided into two coaxial discs which are rotated relative to each other, so that the effective tooth width fills the worm thread gap from both sides simultaneously<\/td>\nLike the split worm, the two-disc wheel introduces load imbalance between the two discs. The disc that takes the driving flank load carries the full torque on first contact; the second disc is loaded only to the extent that its angular displacement precisely matches the first. Manufacturing and setting this angular relationship accurately enough to share load equally is extremely difficult. The assembly is also inherently stiffer in torsion and more susceptible to fretting between the disc interface faces at the contact zone.<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n

All four methods share the same root problem, stated in the technical literature: adjustments and readjustments interfere with geometrically accurate meshing. They shift the contact profile zone and change its form and size. With this, they decrease the load-carrying capacity and deteriorate efficiency. Each adjustment causes a significant amount of start-up wear. The risk of improper assembly and destruction of the worm gear set is substantial.<\/em><\/p>\n

Duplex worm gears do not create any of these problems. They always permit geometrically accurate tooth contact and very delicate backlash adjustment. The contact area, load-carrying capacity, and actual efficiency are unaffected by adjustment. In addition, because duplex teeth are executed with an involute tooth form, they are insensitive to modifications of the center distance \u2014 for example, caused by worm shaft deflections under load \u2014 which is a further reliability advantage in heavily loaded precision drives.<\/p>\n

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Duplex vs Alternatives \u2014 What Changes After Backlash Adjustment<\/h2>\n

This comparison is the core engineering argument for specifying duplex in precision drives. The “after adjustment” column captures what actually happens to the drive after each backlash readjustment \u2014 the information that determines whether the drive will maintain its positioning accuracy specification over repeated adjustments during service life.<\/p>\n

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\n\n\n\n\n\n\n\n\n\n\n
\u0424\u0430\u043a\u0442\u043e\u0440<\/th>\nDuplex Worm (axial shift)<\/th>\nEccentric Hub (center shift)<\/th>\nSplit Worm \/ Split Wheel<\/th>\n<\/tr>\n<\/thead>\n
Contact geometry after adjustment<\/strong><\/td>\nUnchanged \u2014 geometrically accurate at all positions<\/td>\nShifted toward tip or root \u2014 contact area reduced<\/td>\nPeriodic irregularity at split plane \u2014 vibration pulse<\/td>\n<\/tr>\n
Load capacity after adjustment<\/strong><\/td>\nUnaffected \u2014 same as before adjustment<\/td>\nReduced \u2014 smaller effective contact area<\/td>\nReduced \u2014 load imbalance between split halves<\/td>\n<\/tr>\n
Start-up wear on adjustment<\/strong><\/td>\nNone \u2014 smooth repositioning, no new contact zone<\/td>\nSignificant \u2014 new contact zone must bed in each time<\/td>\nSignificant \u2014 split-plane irregularity causes wear spike<\/td>\n<\/tr>\n
Center distance sensitivity<\/strong><\/td>\nInsensitive \u2014 involute form accommodates center distance variation<\/td>\nSensitive \u2014 must return precisely to design center distance<\/td>\nSensitive \u2014 angular alignment of halves must be precise<\/td>\n<\/tr>\n
Adjustment repeatability<\/strong><\/td>\nExcellent \u2014 same axial shift restores same backlash each time<\/td>\nVariable \u2014 eccentric position must be set and locked precisely<\/td>\nPoor \u2014 half-position alignment is difficult to repeat<\/td>\n<\/tr>\n
Assembly risk<\/strong><\/td>\nLow \u2014 clear arrow marks prevent incorrect orientation<\/td>\nModerate \u2014 eccentric lock must be correctly set<\/td>\nHigh \u2014 incorrect half rotation causes immediate tooth damage<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n

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Critical Assembly Instructions \u2014 Must Read Before Installation<\/h2>\n

Duplex worm gears differ in module between the right and left tooth surfaces. This asymmetry means the set has a specific correct orientation \u2014 and only one correct orientation. Installing the worm in the wrong direction causes the center distance to be larger than nominal, making assembly difficult and producing incorrect tooth engagement that cannot be corrected by axial adjustment. Please verify both aspects below before assembly.<\/p>\n

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1. Verifying the Orientation of the Assembly<\/h3>\n

An arrow indicating the correct orientation of assembly is stamped on both the duplex worm and the worm wheel. When assembling, position the worm wheel so that its arrow mark faces toward the front (toward you). Orient the worm so that the direction of its arrow mark coincides with the direction of the wheel’s arrow mark \u2014 both arrows pointing the same way. Should the assembly be incorrect, the center distance “a” will become greater than the nominal design value, resulting in difficulty completing the assembly and, if forced, improper gear engagement that produces excessive noise, vibration, and accelerated tooth wear from the first revolution.<\/p>\n

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2. Verifying the Reference Position for Zero Backlash<\/h3>\n

A V-groove (60\u00b0, 0.3 mm deep) machined on the tip peripheral of one specific duplex worm tooth marks the reference tooth. This reference tooth is the tooth at the axial position that produces near-zero backlash (\u00b10.045 mm) when positioned in alignment with the center of rotation of the worm wheel, with the center distance set at the nominal design value “a.” The procedure for setting zero backlash is: (1) set the housing center distance to the nominal value “a”; (2) rotate the worm until the V-groove reference tooth is aligned with the wheel’s rotation axis; (3) lock the worm housing or bearing adjustment at this position. For applications requiring slightly positive backlash (to accommodate thermal expansion or to prevent tooth binding under load), shift the worm axially toward the thin end by the calculated amount before locking.<\/p>\n

\u2691 Service Note:<\/span> As the gear set wears in service and backlash increases, shift the worm axially toward the thick end by the required amount (calculated from the lead difference specification provided with each set). This readjustment restores the original near-zero backlash without dismantling the gearbox \u2014 in most designs, the worm shaft axial position is adjustable via a threaded end cap or shim stack. Recalibrate the backlash measurement instrument after each adjustment to confirm the restored value before returning the machine to service.<\/p>\n

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Applications \u2014 Where Backlash Control Is Safety-Critical or Accuracy-Limiting<\/h2>\n

Duplex worm gears are specified wherever backlash is unwanted or can be harmful: to maintain repeated high-precision positioning in both directions, to prevent impulse-loaded damage when contact flanks alternate, and in drives where positioning error accumulates over time. Typical applications include rotary and tilting tables, milling machines, and presses. The following examples provide the engineering context for each application’s specific backlash requirement.<\/p>\n