{"id":755,"date":"2026-06-23T09:46:46","date_gmt":"2026-06-23T09:46:46","guid":{"rendered":"https:\/\/oldhamcoupling.net\/product\/ep6-25-set-screw-oldham-coupling\/"},"modified":"2026-06-24T08:47:40","modified_gmt":"2026-06-24T08:47:40","slug":"ep6-25-set-screw-oldham-coupling","status":"publish","type":"product","link":"https:\/\/oldhamcoupling.net\/th\/product\/ep6-25-set-screw-oldham-coupling\/","title":{"rendered":"EP6-25 Set Screw Oldham Coupling"},"content":{"rendered":"
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EP6-25 Set Screw Oldham Coupling \u2014 25 mm Three-Piece Flexible Disc for Optical Stages and Metrology Drives<\/h2>\n

Step up from desktop-class drives into the world of precision-instrument actuation, and the next coupling size that earns its keep is the EP6-25 set-screw Oldham coupling<\/strong>. With a 25 mm outside diameter, a 28 mm overall length, and four catalogue bore options (6.35, 8, 9.525, 10 mm), the EP6-25 is sized to span the breakpoint between \u03a68 mm stepper outputs and \u03a610 mm ball-screw inputs that anchors the majority of mid-range linear stages, optical positioners, and benchtop metrology gauges. Its 3.0 N\u00b7m rated torque and 5 800 rpm speed envelope give it a generous safety margin in the typical 1.0\u20132.0 N\u00b7m duty band of these applications.<\/p>\n

What sets the EP6-25 apart from its EP6-20 sibling \u2014 beyond the obvious torque uplift \u2014 is the substantially higher torsional stiffness (125 N\u00b7m\/rad versus 58) and the wider tolerance for parallel misalignment (1.9 mm). For a metrology machine being assembled to a tolerance budget of \u00b10.5 mm per stack-up, that 1.9 mm allowance is the difference between effortless installation and shimming each mount block. And the additional stiffness means that closed-loop velocity bandwidth can be cranked up without the coupling appearing as a torsional pole in the open-loop transfer function.<\/p>\n

Full Specifications<\/h3>\n
\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n
Parameter<\/th>\nValue<\/th>\n<\/tr>\n<\/thead>\n
Model<\/td>\nEP6-25<\/td>\n<\/tr>\n
Outside Diameter (\u03a6D)<\/td>\n25 mm<\/td>\n<\/tr>\n
Overall Length (L)<\/td>\n28 mm<\/td>\n<\/tr>\n
Bore Range (d1 \/ d2)<\/td>\n6.35, 8, 9.525, 10 mm<\/td>\n<\/tr>\n
Rated Torque<\/td>\n3.0 N\u00b7m<\/td>\n<\/tr>\n
Maximum Torque<\/td>\n6.0 N\u00b7m<\/td>\n<\/tr>\n
Maximum Rotational Speed<\/td>\n5 800 rpm<\/td>\n<\/tr>\n
Moment of Inertia<\/td>\n2.8 \u00d7 10\u207b\u2076 kg\u00b7m\u00b2<\/td>\n<\/tr>\n
Static Torsional Stiffness<\/td>\n125 N\u00b7m\/rad<\/td>\n<\/tr>\n
Parallel Misalignment<\/td>\n1.9 mm<\/td>\n<\/tr>\n
Angular Misalignment<\/td>\n3.0\u00b0<\/td>\n<\/tr>\n
Set-screw Thread<\/td>\nM5<\/td>\n<\/tr>\n
Wrench Tightening Torque<\/td>\n4.0 N\u00b7m<\/td>\n<\/tr>\n
Mass (max bore)<\/td>\n24 g<\/td>\n<\/tr>\n
Backlash<\/td>\nZero<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n

\"EP6-25<\/p>\n

Material Composition<\/h3>\n
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Aluminum-Alloy Body<\/h4>\n

The two hubs are CNC-turned from A2017-T4 bar, hard-anodised to a uniform matt-grey finish that is non-reflective \u2014 an underrated feature in optical applications where stray reflections off rotating hardware can degrade alignment laser performance. The hub face is precision-flycut to keep slot parallelism within \u00b10.02 mm.<\/p>\n<\/p><\/div>\n

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Reinforced POM Centre Disc<\/h4>\n

Centre slider is moulded from POM-H homopolymer, a denser grade than the POM-C used in the smaller EP6 series. The choice is deliberate at 3.0 N\u00b7m duty: POM-H provides ~12 % higher tensile strength and noticeably better creep resistance under sustained load. Carbon-loaded and glass-filled variants are available where the duty pushes the upper limit of the catalogue rating.<\/p>\n<\/p><\/div>\n

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High-Tensile Set Screws<\/h4>\n

M5 cup-point set screws to ISO 4029, grade A2-70 stainless. Two per hub at 90\u00b0. The 4.0 N\u00b7m tightening specification gives sufficient pre-load to prevent slip at maximum momentary torque, while remaining within the screw’s elastic range \u2014 repeated removal and refitting will not strip the threads in the aluminum hub.<\/p>\n<\/p><\/div>\n<\/div>\n

Why the Three-Piece Design Wins in Precision Stages<\/h3>\n

In a high-precision linear stage \u2014 say, a microscope auto-focus stage or a coordinate measuring machine probe carrier \u2014 the dominant error sources are the manufacturing tolerances of the mount plates, the perpendicularity of the motor mounting face, and any thermal growth of the housing during a long measurement cycle. A rigid coupling would force all of these errors into the lead-screw bearings and ultimately into the metrology output. A flexure coupling such as a beam or bellows absorbs them, but stores energy as a torsional spring; that stored energy oscillates back through the loop and shows up as a position error proportional to deceleration profile.<\/p>\n

The EP6-25’s three-piece Oldham slider coupling<\/em> architecture transforms misalignment into pure linear slip at two orthogonal interfaces. No torsional spring, no energy storage, no second-harmonic ripple. Equally important, the centre disc decouples lateral and angular degrees of freedom from the rotational degree of freedom in such a way that the load shaft sees an essentially infinite-stiffness 1:1 angular link, while the motor shaft sees an infinitely-compliant lateral link. That asymmetry is exactly what a metrology system needs.<\/p>\n

For background reading on how Oldham couplings compare to bellows, jaw, and beam alternatives, see the Oldham coupling overview<\/a>.<\/p>\n

Industry Applications<\/h3>\n
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<\/span> Coordinate Measuring Machines<\/h4>\n

Driving Z-axis probe heads on bridge-type CMMs. The constant-velocity transmission preserves the metrology accuracy that determines the entire machine’s MPE certification number.<\/p>\n<\/p><\/div>\n

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<\/span> Telescope Mount Drives<\/h4>\n

Hour-angle and declination drives in small research telescopes. Zero backlash is essential for sidereal tracking accuracy.<\/p>\n<\/p><\/div>\n

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<\/span> Laser-cutting Focus Heads<\/h4>\n

Linking Z-axis focus motors to the focal-distance compensator in fibre-laser cutting heads. POM’s electrical insulation isolates the focus motor circuit from the high-current cutting loop.<\/p>\n<\/p><\/div>\n

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<\/span> Chromatography & HPLC Pumps<\/h4>\n

Reciprocating-pump head drives in analytical liquid-chromatography systems. The combination of zero backlash and electrical isolation matches LC-MS hardware requirements precisely.<\/p>\n<\/p><\/div>\n

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\u26a1<\/span> Precision XY Tables<\/h4>\n

Stacked-axis positioning tables in wire-bonders, die-bonders, and electronic-test handlers. The 1.9 mm parallel tolerance forgives generous machine-build budgets.<\/p>\n<\/p><\/div>\n

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<\/span> Cinema Motion Control<\/h4>\n

Slider, jib, and focus-pull motors on motion-control rigs. Smooth, lash-free transmission preserves on-screen motion fidelity.<\/p>\n<\/p><\/div>\n<\/div>\n

\"EP6-25<\/p>\n

Why Choose Ever-power<\/h3>\n
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Quality Credentials<\/h4>\n

Production of the EP6-25 falls under an ISO 9001:2015<\/strong> management framework, with first-article inspection records archived for every customer drawing. Material declarations cover RoHS<\/strong>, REACH SVHC list 235<\/strong>, and conflict-minerals (3TG) status<\/strong>. CE<\/strong> documentation accompanies machinery-directive integrations on request.<\/p>\n

Engineering Customisation<\/h4>\n

Catalogue bores are 6.35 \/ 8 \/ 9.525 \/ 10 mm. Mixed bore combinations are offered without lead-time penalty. Keyway slots (typical 3 \u00d7 1.4 mm to DIN 6885) are broached on request. Special slider materials \u2014 PEEK, PTFE-filled POM, carbon-fibre filled POM \u2014 are released through engineering review.<\/p>\n

Support & Drawing Library<\/h4>\n

Native CAD files are available in STEP, IGES, Parasolid, and SolidWorks<\/strong> format. Application questions are answered within 24 hours<\/strong> by an English-speaking engineering desk that has spent the last decade specifying couplings for metrology and optical OEMs.<\/p>\n<\/div>\n

\"Ever-power<\/p>\n

Customer Reviews & Case Studies<\/h3>\n
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\u2605\u2605\u2605\u2605\u2605<\/p>\n

Switzerland \u2014 CMM Builder<\/h4>\n

Used in:<\/em> Z-axis probe drive of a bridge-type coordinate measuring machine certified to ISO 10360.<\/p>\n

Feedback:<\/em> “The EP6-25 became our standard after laboratory tests showed it added less than 0.2 \u00b5m to the indicated axis error budget. The bellows we previously used contributed roughly 1.5 \u00b5m of velocity-dependent error \u2014 a meaningful improvement in our overall machine spec sheet.”<\/p>\n<\/p><\/div>\n

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\u2605\u2605\u2605\u2605\u2605<\/p>\n

Australia \u2014 Astronomy Instrumentation Lab<\/h4>\n

Used in:<\/em> Declination drive of a 0.5 m research telescope.<\/p>\n

Feedback:<\/em> “Tracking jitter measured at the focal plane dropped by a factor of four after we replaced the previous Lovejoy-style flexible coupling with the EP6-25. Important note: we re-shimmed the motor mount to take full advantage of the 1.9 mm parallel allowance, which made installation noticeably easier.”<\/p>\n<\/p><\/div>\n

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\u2605\u2605\u2605\u2605\u2606<\/p>\n

United Kingdom \u2014 HPLC Manufacturer<\/h4>\n

Used in:<\/em> Reciprocating-piston pump head of an analytical UPLC system.<\/p>\n

Feedback:<\/em> “The constant-velocity output kept our flow-rate ripple well within the 0.05 % specification. Service-life testing on three units crossed 18 months of continuous duty with no measurable slider wear. Four stars only because we had to specify a custom flat-point set-screw for our hardened motor shaft \u2014 that took an extra week.”<\/p>\n<\/p><\/div>\n<\/div>\n

Frequently Asked Questions<\/h3>\n
\nWhat does the centre-disc replace cost? Can it be replaced in the field?<\/summary>\n

Spare POM centre discs for the EP6-25 are available in single-piece quantities and at the price of approximately 25 % of a complete coupling. Field replacement requires only loosening one hub from its shaft \u2014 the slot geometry self-aligns the new disc.<\/p>\n<\/details>\n

\nHow does the EP6-25 behave under reversing-direction duty?<\/summary>\n

The Oldham architecture is symmetric \u2014 clockwise and counter-clockwise responses are mechanically identical. There is no “preferred direction”, and zero backlash means a step reversal in the host servo is faithfully reproduced at the load.<\/p>\n<\/details>\n

\nWhat is the recommended operating temperature range?<\/summary>\n

Standard POM slider operates from \u221240 \u00b0C to +100 \u00b0C without de-rating. Beyond +100 \u00b0C, a derated torque curve applies; PEEK slider variants extend the useful range to +260 \u00b0C. Consult engineering for documented torque-vs-temperature plots.<\/p>\n<\/details>\n

\nCan two EP6-25 couplings be stacked for greater misalignment compensation?<\/summary>\n

Yes \u2014 a “double Oldham” arrangement with an intermediate spacer extends parallel compensation roughly proportional to the spacer length. This is a recognised technique in stages where motor-to-load offset exceeds the 1.9 mm single-coupling allowance. Ask engineering for a tandem-mount drawing.<\/p>\n<\/details>\n

\nIs keyway-broaching available on the standard 10 mm bore?<\/summary>\n

Yes. A 3 \u00d7 1.4 mm keyway to DIN 6885 \/ JIS B 1301 is the most common; alternative keyway depths and widths are produced regularly. Add roughly 5 working days to standard lead time for a keyway-broached order.<\/p>\n<\/details>\n

Ready to Specify the EP6-25?<\/h3>\n

For OEMs designing precision stages, scientific instruments, and metrology hardware, the EP6-25 is one of the most-specified mid-range Oldham couplings on the market. Explore our complete flexible coupling catalogue<\/a>, read about Ever-power’s precision-manufacturing background<\/a>, or submit a B2B enquiry below.<\/p>\n

\n Request EP6-25 Quote \u2192<\/a>\n<\/p>\n