The LMK8LUU Long Square Flange 8mm Linear Motion Bearing is an extended-length, high-precision linear bushing engineered for smooth, low-friction axial guidance along 8mm hardened optical shafts. Built with an integrated square mounting flange, dual-length recirculating steel ball circuits, and synthetic rubber lip seals on both ends, this extended bearing provides superior moment-load resistance, high rigidity, and effortless bolt-on mounting for 3D printer gantries, CNC slide tables, and robotic linear actuators.

Specification

• Bearing Model: LMK8LUU (Long Type / Square Flange Series)
• Nominal Shaft Diameter (Bore ID): 8mm
• Outer Cylinder Diameter (OD): Approx. 15mm
• Total Bearing Length: Approx. 45mm
• Flange Type: Square Solid Mounting Flange
• Flange Width / Dimension: Approx. 25mm x 25mm
• Flange Thickness: Approx. 5.0mm
• Mounting Hole Configuration: 4 x Pre-Drilled Mounting Holes (PCD approx. 19mm - 20mm)
• Mounting Hole Diameter: Approx. 3.5mm (Compatible with standard M3 socket screws)
• Bearing Shell Material: High-Grade GCr15 High-Carbon Chromium Bearing Steel (Hardened & Polished)
• Internal Retainer Material: Low-Friction Engineering Polymer / POM Resin Cage
• Sealing Configuration: Dual-Sided NBR Synthetic Rubber Wiper Seals (UU Designation)
• Basic Dynamic Load Rating (C): Approx. 431 N
• Basic Static Load Rating (Co): Approx. 784 N
• Compatibility: Fits standard 8mm smooth precision optical rods and linear guide shafts (h6 / g6 tolerance).

Features

• Extended Double-Length Structure: The 45mm extended body houses dual-length recirculating ball tracks, delivering greater load distribution and higher resistance to tilting and radial moment loads compared to standard short LMK8UU bearings.
• Integrated Rigid Square Flange: Precision-ground perpendicular square flange allows direct face-mounting against gantry plates or moving carriages using four M3 screws, eliminating the need for bulky separate bearing pillow blocks.
• Smooth Recirculating Ball Circuits: Incorporates micro-polished chrome steel balls running in closed recirculating raceways to deliver ultra-low friction, high positional accuracy, and smooth, quiet travel.
• Dual Integrated Dust and Wiper Seals: Fitted with NBR rubber contact wiper seals on both ends to retain internal lubrication grease while actively scraping away dust, plastic strings, and workshop particles from the 8mm shaft.
• Hardened and Ground Bearing Steel Body: The outer steel casing is heat-treated and case-hardened for superior wear resistance, dimensional stability, and long mechanical operating life under continuous cycling.

Common Applications

• 3D Printer Gantries and Beds: Guiding vertical Z-axis dual towers, horizontal X-axis carriages, and Y-axis print beds on custom RepRap, CoreXY, and DIY i3-style 3D printers.
• Desktop CNC Routers & Laser Cutters: Supporting lightweight linear motion stages, diode laser carriages, and small PCB milling machine slide tables.
• Robotics & Automated Pick-and-Place: Serving as precision linear guides for robotic end-effectors, test fixture slides, and linear slider actuators.
• Camera Sliders & Laboratory Jigs: Providing smooth, low-vibration tracking rails for motorized camera sliders, optical test benches, and analytical equipment carriages.

Professional Installation and Maintenance Tips

• Pre-Lubricate Before Initial Operation: Factory bearings are shipped with an anti-corrosion protective oil. Clean and inject a quality lithium-based grease or PTFE-infused linear bearing grease through the seals into the ball tracks before final assembly to ensure smooth motion and prevent premature ball wear.
• Align Parallel Guide Rods Carefully: When using dual parallel 8mm shafts, ensure rods are perfectly parallel throughout their entire stroke length before tightening the square flange bolts. Misalignment causes mechanical binding, rough motion, and accelerated ball track wear.
• Do Not Force Over Shaft Chamfers: Never hammer or force the bearing onto an un-chamfered or burred rod end. Ensure the 8mm shaft has a smooth, deburred lead-in chamfer to avoid dislodging the internal ball bearings or damaging the delicate rubber wiper seals during slide-on installation.
• Torque Flange Bolts Evenly: Tighten the four M3 mounting bolts incrementally in an alternating diagonal cross pattern to ensure the flange seats flat against the mounting surface without inducing internal bearing strain.