Backlash and pairings in technopolymer gears<\/title>\n\n <link rel=\"preconnect\" href=\"https:\/\/fonts.googleapis.com\">\n <link rel=\"preconnect\" href=\"https:\/\/fonts.gstatic.com\" crossorigin=\"\">\n <link href=\"https:\/\/fonts.googleapis.com\/css2?family=Inter:wght@400;500;600;700&display=swap\" rel=\"stylesheet\">\n\n <style>\n *, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }\n\n :root {\n --green: #1a6b3c;\n --green-dark: #0f4a28;\n --green-mid: #2d8a55;\n --green-light: #e8f4ed;\n --green-xlight: #f2faf5;\n --amber: #b45309;\n --amber-light: #fef3c7;\n\n --bg: #ffffff;\n --bg-soft: #f8f9fa;\n --bg-muted: #f1f3f5;\n --border: #e5e7eb;\n --border-mid: #d1d5db;\n\n --text-primary: #111827;\n --text-secondary: #4b5563;\n --text-muted: #9ca3af;\n\n --radius-sm: 6px;\n --radius-md: 8px;\n --radius-lg: 12px;\n --shadow-sm: 0 1px 3px rgba(0,0,0,.06), 0 1px 2px rgba(0,0,0,.04);\n --shadow-md: 0 4px 12px rgba(0,0,0,.08), 0 2px 4px rgba(0,0,0,.04);\n }\n\n body { min-height: 100vh; 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}\n\n .badge {\n display: inline-block;\n font-size: 12px;\n font-weight: 600;\n padding: 2px 8px;\n border-radius: 20px;\n background: var(--green-light);\n color: var(--green-dark);\n }\n\n \/* ============================================================\n RESPONSIVE\n ============================================================ *\/\n @media (max-width: 900px) {\n .article-body { flex-direction: column; padding: 20px 20px 48px; }\n }\n \n \/* Glossary tooltips *\/\n .glossary-term {\n border-bottom: 1px dotted var(--green);\n color: var(--green);\n font-style: italic;\n cursor: help;\n }\n .glossary-tooltip {\n position: fixed;\n z-index: 9999;\n background: #fff;\n border: 1px solid var(--border-mid);\n border-radius: var(--radius-md);\n box-shadow: var(--shadow-md);\n padding: 10px 14px;\n max-width: 300px;\n font-family: 'Inter', sans-serif;\n font-size: 13px;\n }\n .glossary-tooltip__title {\n font-weight: 600;\n color: var(--text-primary);\n margin-bottom: 4px;\n }\n .glossary-tooltip__def {\n font-size: 12.5px;\n color: var(--text-secondary);\n line-height: 1.6;\n }\n .glossary-tooltip__tag {\n display: inline-block;\n margin-top: 6px;\n font-size: 9px;\n font-weight: 600;\n padding: 2px 7px;\n border-radius: 20px;\n background: var(--green-light);\n color: var(--green-dark);\n text-transform: uppercase;\n letter-spacing: 0.04em;\n }\n\n <\/style>\n<\/head>\n<body>\n\n<div id=\"tt-gioco-di-flanchi-backlash\" class=\"glossary-tooltip\" hidden=\"\">\n <div class=\"glossary-tooltip__title\">Backlash<\/div>\n <div class=\"glossary-tooltip__def\">Free clearance between the flanks of two mating teeth, measured at the pitch circle. It prevents jamming due to thermal expansion or assembly errors.<\/div>\n <span class=\"glossary-tooltip__tag\">Glossary<\/span>\n<\/div>\n<div id=\"tt-diametro-primitivo\" class=\"glossary-tooltip\" hidden=\"\">\n <div class=\"glossary-tooltip__title\">Pitch diameter<\/div>\n <div class=\"glossary-tooltip__def\">Diameter of the theoretical circle at which contact occurs between two meshing gears. Obtained from the product of the module and the number of teeth.<\/div>\n <span class=\"glossary-tooltip__tag\">Glossary<\/span>\n<\/div>\n<div id=\"tt-evolvente\" class=\"glossary-tooltip\" hidden=\"\">\n <div class=\"glossary-tooltip__title\">Involute<\/div>\n <div class=\"glossary-tooltip__def\">Geometric curve defining the tooth flank profile. Generated by unwrapping a straight line that rolls without slipping on a base circle. It ensures a constant transmission ratio even in the presence of small centre-distance errors.<\/div>\n <span class=\"glossary-tooltip__tag\">Glossary<\/span>\n<\/div>\n\n <div class=\"article-page\">\n <div class=\"article-body\">\n <div class=\"article-body__main\"><script type=\"application\/ld+json\">\n{\n \"@context\": \"https:\/\/schema.org\",\n \"@graph\": [\n {\n \"@type\": \"TechArticle\",\n \"@id\": \"#article\",\n \"headline\": \"Backlash and pairings in technopolymer gears\",\n \"description\": \"Tooth backlash isn't a machining defect. It's a design parameter, and in technopolymers it must be calculated with more care than in steel: thermal expansion and moisture absorption change tooth dimensions in service, not just in the workshop.\",\n \"inLanguage\": \"en\",\n \"mentions\": [\n {\n \"@id\": \"#term-gioco-di-flanchi-backlash\"\n },\n {\n \"@id\": \"#term-diametro-primitivo\"\n },\n {\n \"@id\": \"#term-evolvente\"\n }\n ]\n },\n {\n \"@type\": \"DefinedTermSet\",\n \"@id\": \"#glossario\",\n \"name\": \"Glossario - Backlash and pairings in technopolymer gears\",\n \"hasDefinedTerm\": [\n {\n \"@type\": \"DefinedTerm\",\n \"@id\": \"#term-gioco-di-flanchi-backlash\",\n \"name\": \"Backlash\",\n \"description\": \"Free clearance between the flanks of two mating teeth, measured at the pitch circle. 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It ensures a constant transmission ratio even in the presence of small centre-distance errors.\",\n \"inDefinedTermSet\": \"#glossario\"\n }\n ]\n }\n ]\n}\n<\/script>\n\n\n\n <h1 class=\"article__title\">Backlash and pairings in technopolymer gears<\/h1>\n<p class=\"article__subtitle\">Tooth <dfn id=\"def-gioco-di-flanchi-backlash\"><span class=\"glossary-term\" data-tooltip=\"tt-gioco-di-flanchi-backlash\" title=\"Free clearance between the flanks of two mating teeth, measured at the pitch circle. It prevents jamming due to thermal expansion or assembly errors.\">backlash<\/span><\/dfn> isn’t a machining defect. It’s a design parameter, and in technopolymers it must be calculated with more care than in steel: thermal expansion and moisture absorption change tooth dimensions in service, not just in the workshop.<\/p>\n<h2 class=\"article__h2\" id=\"tooth-backlash-definition-and-function\">\n <span class=\"article__h2-icon\"><svg xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"16\" height=\"16\" viewBox=\"0 0 24 24\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\" stroke-linecap=\"round\" stroke-linejoin=\"round\"><polyline points=\"5 9 2 12 5 15\"><\/polyline><polyline points=\"9 5 12 2 15 5\"><\/polyline><polyline points=\"15 19 12 22 9 19\"><\/polyline><polyline points=\"19 9 22 12 19 15\"><\/polyline><line x1=\"2\" y1=\"12\" x2=\"22\" y2=\"12\"><\/line><line x1=\"12\" y1=\"2\" x2=\"12\" y2=\"22\"><\/line><\/svg><\/span>\n Tooth backlash: definition and function\n<\/h2>\n<p class=\"article__p\"><strong>Tooth backlash<\/strong> (the gap between tooth flanks measured on the pitch circle) is the difference between the space width and the tooth thickness. In the ideal transmission backlash is zero, but in reality it’s always present and necessary. It serves to compensate for pitch errors, elastic deformation, thermal expansion and, in the case of technopolymers, moisture absorption.<\/p>\n<div class=\"warnbox\">\n <div class=\"warnbox__title\">\n <svg xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"14\" height=\"14\" viewBox=\"0 0 24 24\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\" stroke-linecap=\"round\" stroke-linejoin=\"round\"><path d=\"M10.29 3.86L1.82 18a2 2 0 0 0 1.71 3h16.94a2 2 0 0 0 1.71-3L13.71 3.86a2 2 0 0 0-3.42 0z\"><\/path><line x1=\"12\" y1=\"9\" x2=\"12\" y2=\"13\"><\/line><line x1=\"12\" y1=\"17\" x2=\"12.01\" y2=\"17\"><\/line><\/svg>\n Warning\n <\/div>\n <p class=\"warnbox__text\">Insufficient backlash leads to seizing or accelerated wear from interference. Excessive backlash increases impact noise and the angular play of the transmission. There’s no universal value: it must be calculated for each material-temperature pair.<\/p>\n<\/div>\n<h2 class=\"article__h2\" id=\"the-problem-of-thermal-expansion\">\n <span class=\"article__h2-icon\"><svg xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"16\" height=\"16\" viewBox=\"0 0 24 24\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\" stroke-linecap=\"round\" stroke-linejoin=\"round\"><path d=\"M14 14.76V3.5a2.5 2.5 0 0 0-5 0v11.26a4.5 4.5 0 1 0 5 0z\"><\/path><\/svg><\/span>\n The problem of thermal expansion\n<\/h2>\n<p class=\"article__p\">The thermal expansion coefficient of POM-C is <strong>about 110 \u00d7 10\u207b\u2076 \/K<\/strong>, nearly 10 times that of steel. On a gear with module 2 and 30 teeth (<dfn id=\"def-diametro-primitivo\"><span class=\"glossary-term\" data-tooltip=\"tt-diametro-primitivo\" title=\"Diameter of the theoretical circle at which contact occurs between two meshing gears. Obtained from the product of the module and the number of teeth.\">pitch diameter<\/span><\/dfn> 60 mm), a temperature change of 40\u00b0C produces a diameter change of about 0.26 mm.<\/p>\n<p class=\"article__p\">The assembly clearance must therefore account not only for the dimensional tolerance of the profile, but also for the thermal swing expected in service.<\/p>\n<div class=\"infobox infobox--grey\">\n <div class=\"infobox__title\">\n <svg xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"14\" height=\"14\" viewBox=\"0 0 24 24\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\" stroke-linecap=\"round\" stroke-linejoin=\"round\"><path d=\"M14.7 6.3a1 1 0 0 0 0 1.4l1.6 1.6a1 1 0 0 0 1.4 0l3.77-3.77a6 6 0 0 1-7.94 7.94l-6.91 6.91a2.12 2.12 0 0 1-3-3l6.91-6.91a6 6 0 0 1 7.94-7.94l-3.76 3.76z\"><\/path><\/svg>\n Technical note\n <\/div>\n <p class=\"infobox__text\">If the pinion is POM-C and the wheel is steel, the differential expansion is at its maximum. In these configurations, calculate the initial clearance under the most unfavorable temperature conditions before deciding the profile tolerances.<\/p>\n<\/div>\n<p class=\"article__p\">The same reasoning applies to PA6: moisture absorption produces an additional dimensional change on top of thermal expansion alone. PA6, POM-C and PK answer to different application logics. <strong>PA6<\/strong> offers the highest mechanical strength among the three and an excellent cost\/performance ratio; in humid environments it requires including the dimensional change from absorption in the clearance calculation, a parameter managed at the design stage. <strong>POM-C<\/strong> is preferable when dimensional stability is the priority and loads are moderate. <strong>PK<\/strong> is the choice for chemically aggressive environments or when you want to minimize maintenance.<\/p>\n<h2 class=\"article__h2\" id=\"practical-measurement-of-backlash\">\n <span class=\"article__h2-icon\"><svg xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"16\" height=\"16\" viewBox=\"0 0 24 24\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\" stroke-linecap=\"round\" stroke-linejoin=\"round\"><path d=\"M7 16.3c2.2 0 4-1.83 4-4.05 0-1.16-.57-2.26-1.71-3.19S7.29 6.75 7 5.3c-.29 1.45-1.14 2.84-2.29 3.76S3 11.09 3 12.25c0 2.22 1.8 4.05 4 4.05z\"><\/path><path d=\"M12.56 6.6A10.97 10.97 0 0 0 14 3.02c.5 2.5 2 4.9 4 6.5s3 3.5 3 5.5a6.98 6.98 0 0 1-11.91 4.97\"><\/path><\/svg><\/span>\n Practical measurement of backlash\n<\/h2>\n<p class=\"article__p\">The simplest method to check backlash on an assembled pair is the lead (or wax) method: place a deformable lead wire between the teeth during a full rotation, then measure the squashed thickness with a micrometer.<\/p>\n<p class=\"article__p\">For small gears (module below 2), use a dial indicator with one gear locked and the other oscillating.<\/p>\n<h2 class=\"article__h2\" id=\"watch-out-for-fixed-center-distances\">\n <span class=\"article__h2-icon\"><svg xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"16\" height=\"16\" viewBox=\"0 0 24 24\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\" stroke-linecap=\"round\" stroke-linejoin=\"round\"><circle cx=\"12\" cy=\"12\" r=\"10\"><\/circle><\/svg><\/span>\n Watch out for fixed center distances\n<\/h2>\n<p class=\"article__p\">When the center distance is imposed by the structure (for example, holes already present in sheet metal) and isn’t adjustable, the backlash depends exclusively on the combination of tolerances on the profile and on the diameters.<\/p>\n<p class=\"article__p\">In this case specify the <dfn id=\"def-evolvente\"><span class=\"glossary-term\" data-tooltip=\"tt-evolvente\" title=\"Geometric curve defining the tooth flank profile. Generated by unwrapping a straight line that rolls without slipping on a base circle. It ensures a constant transmission ratio even in the presence of small centre-distance errors.\">involute<\/span><\/dfn>-profile tolerances according to the <strong>ISO 1328<\/strong> classes and check the minimum backlash under the most unfavorable temperature and moisture conditions.<\/p>\n<div class=\"infobox infobox--grey\">\n <div class=\"infobox__title\">\n <svg xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"14\" height=\"14\" viewBox=\"0 0 24 24\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\" stroke-linecap=\"round\" stroke-linejoin=\"round\"><line x1=\"9\" y1=\"18\" x2=\"15\" y2=\"18\"><\/line><line x1=\"10\" y1=\"22\" x2=\"14\" y2=\"22\"><\/line><path d=\"M15.09 14c.18-.98.65-1.74 1.41-2.5A4.65 4.65 0 0 0 18 8 6 6 0 0 0 6 8c0 1 .23 2.23 1.5 3.5A4.61 4.61 0 0 1 8.91 14\"><\/path><\/svg>\n From the field\n <\/div>\n <p class=\"infobox__text\">In our experience, most seizures on technopolymer pairs with a fixed center distance occur in the first hours of hot operation: the backlash had been checked cold, but not under the real operating conditions.<\/p>\n<\/div>\n<div class=\"infobox\">\n <div class=\"infobox__title\">\n <svg xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"14\" height=\"14\" viewBox=\"0 0 24 24\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\" stroke-linecap=\"round\" stroke-linejoin=\"round\"><path d=\"M4 4h16c1.1 0 2 .9 2 2v12c0 1.1-.9 2-2 2H4c-1.1 0-2-.9-2-2V6c0-1.1.9-2 2-2z\"><\/path><polyline points=\"22,6 12,13 2,6\"><\/polyline><\/svg>\n Ask us\n <\/div>\n <p class=\"infobox__text\">If your application involves high thermal swings, mixed materials or non-adjustable center distances, <a href=\"https:\/\/shop.stagnoligears.com\/en\/contacts\/\" target=\"_blank\" rel=\"noopener\" class=\"cta-link\">write<\/a> to the technical office: we calculate the most suitable backlash configuration for you.<\/p>\n<\/div>\n\n <\/div>\n <\/div>\n <\/div>\n\n\n<script>\n (function () {\n var hideTimers = {};\n function 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{"id":25591,"date":"2026-06-30T10:38:24","date_gmt":"2026-06-30T08:38:24","guid":{"rendered":"https:\/\/shop.stagnoligears.com\/?post_type=centro-tecnico&p=25591"},"modified":"2026-07-10T13:57:48","modified_gmt":"2026-07-10T11:57:48","slug":"backlash-and-pairings-in-technopolymer-gears","status":"publish","type":"centro-tecnico","link":"https:\/\/shop.stagnoligears.com\/en\/technical-hub\/backlash-and-pairings-in-technopolymer-gears\/","title":{"rendered":"Backlash and pairings in technopolymer gears"},"content":{"rendered":"\n\n \n \n \n Backlash and pairings in technopolymer gears<\/title>\n\n <link rel=\"preconnect\" href=\"https:\/\/fonts.googleapis.com\">\n <link rel=\"preconnect\" href=\"https:\/\/fonts.gstatic.com\" crossorigin=\"\">\n <link href=\"https:\/\/fonts.googleapis.com\/css2?family=Inter:wght@400;500;600;700&display=swap\" rel=\"stylesheet\">\n\n <style>\n *, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }\n\n :root {\n --green: #1a6b3c;\n --green-dark: #0f4a28;\n --green-mid: #2d8a55;\n --green-light: #e8f4ed;\n --green-xlight: #f2faf5;\n --amber: #b45309;\n --amber-light: #fef3c7;\n\n --bg: #ffffff;\n --bg-soft: #f8f9fa;\n --bg-muted: #f1f3f5;\n --border: #e5e7eb;\n --border-mid: #d1d5db;\n\n --text-primary: #111827;\n --text-secondary: #4b5563;\n --text-muted: #9ca3af;\n\n --radius-sm: 6px;\n --radius-md: 8px;\n --radius-lg: 12px;\n --shadow-sm: 0 1px 3px rgba(0,0,0,.06), 0 1px 2px rgba(0,0,0,.04);\n --shadow-md: 0 4px 12px rgba(0,0,0,.08), 0 2px 4px rgba(0,0,0,.04);\n }\n\n body { min-height: 100vh; 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}\n\n .badge {\n display: inline-block;\n font-size: 12px;\n font-weight: 600;\n padding: 2px 8px;\n border-radius: 20px;\n background: var(--green-light);\n color: var(--green-dark);\n }\n\n \/* ============================================================\n RESPONSIVE\n ============================================================ *\/\n @media (max-width: 900px) {\n .article-body { flex-direction: column; padding: 20px 20px 48px; }\n }\n \n \/* Glossary tooltips *\/\n .glossary-term {\n border-bottom: 1px dotted var(--green);\n color: var(--green);\n font-style: italic;\n cursor: help;\n }\n .glossary-tooltip {\n position: fixed;\n z-index: 9999;\n background: #fff;\n border: 1px solid var(--border-mid);\n border-radius: var(--radius-md);\n box-shadow: var(--shadow-md);\n padding: 10px 14px;\n max-width: 300px;\n font-family: 'Inter', sans-serif;\n font-size: 13px;\n }\n .glossary-tooltip__title {\n font-weight: 600;\n color: var(--text-primary);\n margin-bottom: 4px;\n }\n .glossary-tooltip__def {\n font-size: 12.5px;\n color: var(--text-secondary);\n line-height: 1.6;\n }\n .glossary-tooltip__tag {\n display: inline-block;\n margin-top: 6px;\n font-size: 9px;\n font-weight: 600;\n padding: 2px 7px;\n border-radius: 20px;\n background: var(--green-light);\n color: var(--green-dark);\n text-transform: uppercase;\n letter-spacing: 0.04em;\n }\n\n <\/style>\n<\/head>\n<body>\n\n<div id=\"tt-gioco-di-flanchi-backlash\" class=\"glossary-tooltip\" hidden=\"\">\n <div class=\"glossary-tooltip__title\">Backlash<\/div>\n <div class=\"glossary-tooltip__def\">Free clearance between the flanks of two mating teeth, measured at the pitch circle. It prevents jamming due to thermal expansion or assembly errors.<\/div>\n <span class=\"glossary-tooltip__tag\">Glossary<\/span>\n<\/div>\n<div id=\"tt-diametro-primitivo\" class=\"glossary-tooltip\" hidden=\"\">\n <div class=\"glossary-tooltip__title\">Pitch diameter<\/div>\n <div class=\"glossary-tooltip__def\">Diameter of the theoretical circle at which contact occurs between two meshing gears. Obtained from the product of the module and the number of teeth.<\/div>\n <span class=\"glossary-tooltip__tag\">Glossary<\/span>\n<\/div>\n<div id=\"tt-evolvente\" class=\"glossary-tooltip\" hidden=\"\">\n <div class=\"glossary-tooltip__title\">Involute<\/div>\n <div class=\"glossary-tooltip__def\">Geometric curve defining the tooth flank profile. Generated by unwrapping a straight line that rolls without slipping on a base circle. It ensures a constant transmission ratio even in the presence of small centre-distance errors.<\/div>\n <span class=\"glossary-tooltip__tag\">Glossary<\/span>\n<\/div>\n\n <div class=\"article-page\">\n <div class=\"article-body\">\n <div class=\"article-body__main\"><script type=\"application\/ld+json\">\n{\n \"@context\": \"https:\/\/schema.org\",\n \"@graph\": [\n {\n \"@type\": \"TechArticle\",\n \"@id\": \"#article\",\n \"headline\": \"Backlash and pairings in technopolymer gears\",\n \"description\": \"Tooth backlash isn't a machining defect. 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It ensures a constant transmission ratio even in the presence of small centre-distance errors.\",\n \"inDefinedTermSet\": \"#glossario\"\n }\n ]\n }\n ]\n}\n<\/script>\n\n\n\n <h1 class=\"article__title\">Backlash and pairings in technopolymer gears<\/h1>\n<p class=\"article__subtitle\">Tooth <dfn id=\"def-gioco-di-flanchi-backlash\"><span class=\"glossary-term\" data-tooltip=\"tt-gioco-di-flanchi-backlash\" title=\"Free clearance between the flanks of two mating teeth, measured at the pitch circle. It prevents jamming due to thermal expansion or assembly errors.\">backlash<\/span><\/dfn> isn’t a machining defect. It’s a design parameter, and in technopolymers it must be calculated with more care than in steel: thermal expansion and moisture absorption change tooth dimensions in service, not just in the workshop.<\/p>\n<h2 class=\"article__h2\" id=\"tooth-backlash-definition-and-function\">\n <span class=\"article__h2-icon\"><svg xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"16\" height=\"16\" viewBox=\"0 0 24 24\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\" stroke-linecap=\"round\" stroke-linejoin=\"round\"><polyline points=\"5 9 2 12 5 15\"><\/polyline><polyline points=\"9 5 12 2 15 5\"><\/polyline><polyline points=\"15 19 12 22 9 19\"><\/polyline><polyline points=\"19 9 22 12 19 15\"><\/polyline><line x1=\"2\" y1=\"12\" x2=\"22\" y2=\"12\"><\/line><line x1=\"12\" y1=\"2\" x2=\"12\" y2=\"22\"><\/line><\/svg><\/span>\n Tooth backlash: definition and function\n<\/h2>\n<p class=\"article__p\"><strong>Tooth backlash<\/strong> (the gap between tooth flanks measured on the pitch circle) is the difference between the space width and the tooth thickness. In the ideal transmission backlash is zero, but in reality it’s always present and necessary. It serves to compensate for pitch errors, elastic deformation, thermal expansion and, in the case of technopolymers, moisture absorption.<\/p>\n<div class=\"warnbox\">\n <div class=\"warnbox__title\">\n <svg xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"14\" height=\"14\" viewBox=\"0 0 24 24\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\" stroke-linecap=\"round\" stroke-linejoin=\"round\"><path d=\"M10.29 3.86L1.82 18a2 2 0 0 0 1.71 3h16.94a2 2 0 0 0 1.71-3L13.71 3.86a2 2 0 0 0-3.42 0z\"><\/path><line x1=\"12\" y1=\"9\" x2=\"12\" y2=\"13\"><\/line><line x1=\"12\" y1=\"17\" x2=\"12.01\" y2=\"17\"><\/line><\/svg>\n Warning\n <\/div>\n <p class=\"warnbox__text\">Insufficient backlash leads to seizing or accelerated wear from interference. Excessive backlash increases impact noise and the angular play of the transmission. There’s no universal value: it must be calculated for each material-temperature pair.<\/p>\n<\/div>\n<h2 class=\"article__h2\" id=\"the-problem-of-thermal-expansion\">\n <span class=\"article__h2-icon\"><svg xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"16\" height=\"16\" viewBox=\"0 0 24 24\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\" stroke-linecap=\"round\" stroke-linejoin=\"round\"><path d=\"M14 14.76V3.5a2.5 2.5 0 0 0-5 0v11.26a4.5 4.5 0 1 0 5 0z\"><\/path><\/svg><\/span>\n The problem of thermal expansion\n<\/h2>\n<p class=\"article__p\">The thermal expansion coefficient of POM-C is <strong>about 110 \u00d7 10\u207b\u2076 \/K<\/strong>, nearly 10 times that of steel. On a gear with module 2 and 30 teeth (<dfn id=\"def-diametro-primitivo\"><span class=\"glossary-term\" data-tooltip=\"tt-diametro-primitivo\" title=\"Diameter of the theoretical circle at which contact occurs between two meshing gears. Obtained from the product of the module and the number of teeth.\">pitch diameter<\/span><\/dfn> 60 mm), a temperature change of 40\u00b0C produces a diameter change of about 0.26 mm.<\/p>\n<p class=\"article__p\">The assembly clearance must therefore account not only for the dimensional tolerance of the profile, but also for the thermal swing expected in service.<\/p>\n<div class=\"infobox infobox--grey\">\n <div class=\"infobox__title\">\n <svg xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"14\" height=\"14\" viewBox=\"0 0 24 24\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\" stroke-linecap=\"round\" stroke-linejoin=\"round\"><path d=\"M14.7 6.3a1 1 0 0 0 0 1.4l1.6 1.6a1 1 0 0 0 1.4 0l3.77-3.77a6 6 0 0 1-7.94 7.94l-6.91 6.91a2.12 2.12 0 0 1-3-3l6.91-6.91a6 6 0 0 1 7.94-7.94l-3.76 3.76z\"><\/path><\/svg>\n Technical note\n <\/div>\n <p class=\"infobox__text\">If the pinion is POM-C and the wheel is steel, the differential expansion is at its maximum. In these configurations, calculate the initial clearance under the most unfavorable temperature conditions before deciding the profile tolerances.<\/p>\n<\/div>\n<p class=\"article__p\">The same reasoning applies to PA6: moisture absorption produces an additional dimensional change on top of thermal expansion alone. PA6, POM-C and PK answer to different application logics. <strong>PA6<\/strong> offers the highest mechanical strength among the three and an excellent cost\/performance ratio; in humid environments it requires including the dimensional change from absorption in the clearance calculation, a parameter managed at the design stage. <strong>POM-C<\/strong> is preferable when dimensional stability is the priority and loads are moderate. <strong>PK<\/strong> is the choice for chemically aggressive environments or when you want to minimize maintenance.<\/p>\n<h2 class=\"article__h2\" id=\"practical-measurement-of-backlash\">\n <span class=\"article__h2-icon\"><svg xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"16\" height=\"16\" viewBox=\"0 0 24 24\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\" stroke-linecap=\"round\" stroke-linejoin=\"round\"><path d=\"M7 16.3c2.2 0 4-1.83 4-4.05 0-1.16-.57-2.26-1.71-3.19S7.29 6.75 7 5.3c-.29 1.45-1.14 2.84-2.29 3.76S3 11.09 3 12.25c0 2.22 1.8 4.05 4 4.05z\"><\/path><path d=\"M12.56 6.6A10.97 10.97 0 0 0 14 3.02c.5 2.5 2 4.9 4 6.5s3 3.5 3 5.5a6.98 6.98 0 0 1-11.91 4.97\"><\/path><\/svg><\/span>\n Practical measurement of backlash\n<\/h2>\n<p class=\"article__p\">The simplest method to check backlash on an assembled pair is the lead (or wax) method: place a deformable lead wire between the teeth during a full rotation, then measure the squashed thickness with a micrometer.<\/p>\n<p class=\"article__p\">For small gears (module below 2), use a dial indicator with one gear locked and the other oscillating.<\/p>\n<h2 class=\"article__h2\" id=\"watch-out-for-fixed-center-distances\">\n <span class=\"article__h2-icon\"><svg xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"16\" height=\"16\" viewBox=\"0 0 24 24\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\" stroke-linecap=\"round\" stroke-linejoin=\"round\"><circle cx=\"12\" cy=\"12\" r=\"10\"><\/circle><\/svg><\/span>\n Watch out for fixed center distances\n<\/h2>\n<p class=\"article__p\">When the center distance is imposed by the structure (for example, holes already present in sheet metal) and isn’t adjustable, the backlash depends exclusively on the combination of tolerances on the profile and on the diameters.<\/p>\n<p class=\"article__p\">In this case specify the <dfn id=\"def-evolvente\"><span class=\"glossary-term\" data-tooltip=\"tt-evolvente\" title=\"Geometric curve defining the tooth flank profile. Generated by unwrapping a straight line that rolls without slipping on a base circle. It ensures a constant transmission ratio even in the presence of small centre-distance errors.\">involute<\/span><\/dfn>-profile tolerances according to the <strong>ISO 1328<\/strong> classes and check the minimum backlash under the most unfavorable temperature and moisture conditions.<\/p>\n<div class=\"infobox infobox--grey\">\n <div class=\"infobox__title\">\n <svg xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"14\" height=\"14\" viewBox=\"0 0 24 24\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\" stroke-linecap=\"round\" stroke-linejoin=\"round\"><line x1=\"9\" y1=\"18\" x2=\"15\" y2=\"18\"><\/line><line x1=\"10\" y1=\"22\" x2=\"14\" y2=\"22\"><\/line><path d=\"M15.09 14c.18-.98.65-1.74 1.41-2.5A4.65 4.65 0 0 0 18 8 6 6 0 0 0 6 8c0 1 .23 2.23 1.5 3.5A4.61 4.61 0 0 1 8.91 14\"><\/path><\/svg>\n From the field\n <\/div>\n <p class=\"infobox__text\">In our experience, most seizures on technopolymer pairs with a fixed center distance occur in the first hours of hot operation: the backlash had been checked cold, but not under the real operating conditions.<\/p>\n<\/div>\n<div class=\"infobox\">\n <div class=\"infobox__title\">\n <svg xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"14\" height=\"14\" viewBox=\"0 0 24 24\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\" stroke-linecap=\"round\" stroke-linejoin=\"round\"><path d=\"M4 4h16c1.1 0 2 .9 2 2v12c0 1.1-.9 2-2 2H4c-1.1 0-2-.9-2-2V6c0-1.1.9-2 2-2z\"><\/path><polyline points=\"22,6 12,13 2,6\"><\/polyline><\/svg>\n Ask us\n <\/div>\n <p class=\"infobox__text\">If your application involves high thermal swings, mixed materials or non-adjustable center distances, <a href=\"https:\/\/shop.stagnoligears.com\/en\/contacts\/\" target=\"_blank\" rel=\"noopener\" class=\"cta-link\">write<\/a> to the technical office: we calculate the most suitable backlash configuration for you.<\/p>\n<\/div>\n\n <\/div>\n <\/div>\n <\/div>\n\n\n<script>\n (function () {\n var hideTimers = {};\n function 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})();\n<\/script>\n\n<\/body><\/html>\n","protected":false},"excerpt":{"rendered":"<p>Methods for geometric backlash calculation to compensate for volume changes caused by thermal fluctuations and hygroscopic absorption.<\/p>\n","protected":false},"parent":0,"template":"","meta":{"_acf_changed":false},"campo-applicazione":[5455],"categoria-ct":[5444],"class_list":["post-25591","centro-tecnico","type-centro-tecnico","status-publish","hentry","campo-applicazione-design","categoria-ct-cylindrical-technopolymer-gears"],"acf":[],"yoast_head":"\n<title>Backlash and Pairings in Technopolymer Gears | Stagnoli Gears Shop<\/title>\n<meta name=\"description\" content=\"Learn how tooth backlash works in technopolymer gears and how thermal expansion, moisture absorption and material pairing affect gear performance.\" \/>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" 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