{"id":6192,"date":"2026-10-29T18:00:49","date_gmt":"2026-10-29T09:00:49","guid":{"rendered":"https:\/\/donguri3.net\/server-tech\/3dprint-arm-joint-hinge-2\/"},"modified":"2026-10-29T18:00:50","modified_gmt":"2026-10-29T09:00:50","slug":"3dprint-arm-joint-hinge","status":"publish","type":"post","link":"https:\/\/donguri3.net\/en\/diy-repair\/3d-printer-cnc\/3dprint-arm-joint-hinge\/","title":{"rendered":"3D Printed Design for a 1-Axis Arm Joint for 10mm Square Tubes"},"content":{"rendered":"

Although I introduced a USB microscope for electronics work and checking PCB soldering, the included stand had a narrow range of motion and took up too much workspace. Therefore, I looked for an adjustable arm that would allow me to use my hands freely and be fixed in any desired position, and I purchased an inexpensive arm.<\/p>\n

I couldn’t find the exact same one, but here is a similar product:<\/p>\n

Mobile Monitor Arm, Magnetic Stand, 75x75mm VESA & Tablet Compatible, MagSafe Compatible, Supports 13.3 to 18.5-inch Mobile Monitors<\/a><\/p>\n

However, this commercially available product had structural flaws. No matter how tightly I tightened the screws at the joints, the holding power was completely insufficient, and it wobbled easily with just a slight touch of the hand. For applications requiring minute positioning like a microscope, this wobbling was fatal and impractical.<\/p>\n

On the other hand, the black metal square rods (10mm square) used as the skeleton had sufficient rigidity on their own. Therefore, I decided to remove all the useless joint parts and 3D print my own custom joints that could be locked securely.<\/p>\n

Concept of a High-Rigidity Adjustable Arm Reusing Square Pipes<\/h2>\n

The goal this time was to rebuild a sturdy arm based on the remaining 10mm square metal rods, allowing the working position to be changed freely.<\/p>\n

Instead of the unreliable frictional fixing found in commercial products, I aimed for a hinge structure that maximizes the mechanical tightening force of bolts and nuts. Since the metal pipes provide the skeleton for the entire arm, the 3D-printed parts are specialized for two roles: “secure fastening to the pipes” and “strong frictional force at the joints.”<\/p>\n

Requirements for a Tool-Less, Securely Lockable 1-Axis Joint<\/h2>\n

The targets set for fabrication were as follows:<\/p>\n

    \n
  • Qualitative target: The arm must not sag when a USB microscope is attached to the tip, and vibrations must settle immediately even after making minute position adjustments.<\/li>\n
  • Operability target: Securely tighten and loosen by hand without using tools such as hex wrenches or spanners.<\/li>\n
  • Dimensional accuracy: Press-fit into the 10mm square pipe without rattling, ensuring the connection does not loosen even during long-term use.<\/li>\n<\/ul>\n

    Strength Insufficiency of Resin Parts and Bolt Spinning<\/h2>\n

    When designing movable joints using a typical 3D printer that melts and deposits resin, the following challenges must be overcome:<\/p>\n

      \n
    1. Bolt spinning during tightening
      \nTo firmly fix the joint, a thick M6 class bolt is necessary, but a structure where one side must be held with a tool while turning the knob on the other side does not allow for smooth, one-handed position adjustment. The bolt head must be securely fixed on the resin side.<\/li>\n
    2. Wall thickness and rigidity insufficiency of resin parts
      \nA thin sleeve structure yields and breaks under tightening torque, while making it too thick results in an oversized outer shape. Especially with home 3D printers, if settings create internal cavities (lattice-like gaps), the strength drops significantly.<\/li>\n
    3. Inner diameter shrinkage specific to resin layering
      \nThe opening of the female side where the square pipe is inserted will have a narrowed inner diameter due to the expansion and contraction of the melted resin if printed according to design values, preventing the pipe from entering.<\/li>\n<\/ol>\n

      1.5mm Wall-Thickness Shell Design and Carriage Bolts for Anti-Rotation<\/h2>\n

      I used FreeCAD for CAD software and fabricated using PLA filament. The design innovations incorporated to solve the above challenges are the following three:<\/p>\n

      1.5mm Solid Design and 0.5mm Clearance Setting<\/h3>\n

      The wall thickness of the sleeve part acting as the socket for the square pipe was set to 1.5mm. Based on empirical experience with the affordable 3D printer I use (the LABISTS X1 MINI 3D Printer purchased in 2020), setting the wall thickness to 1.5mm prevents internal cavities from forming in the slicer software, generating a sturdy plate completely filled with outer perimeter wall resin. This achieves a fracture-resistant structure without adding unnecessary thickness.<\/p>\n

      Additionally, considering the characteristic dimensional shrinkage during printing that narrows the inner diameter by about 0.5mm, I modeled the sleeve inner diameter at 10.5mm for a 10mm square rod. This allows the pipe to fit snugly without rattling, with no post-processing such as grinding required. For fixing to the pipe, the hole originally present in the rod was reused, and it is secured through-and-through from the side with an M4 screw.<\/p>\n

      Secure Anti-Rotation via M6 Carriage Bolts<\/h3>\n

      For the movable axis of the joint, I used an M6 carriage bolt (square neck round head bolt), which was a leftover part I had on hand. Since it has a square neck under the head, I designed a square counterbore hole on one side of the joint to seat the square neck. This causes the bolt head to engage with the resin and become completely anti-rotated, entirely preventing the bolt from spinning when tightening from the opposite side.<\/p>\n

      Wrench-Shaped Hand-Tightening Lever<\/h3>\n

      On the tightening side, I designed a dedicated lever part to fit an M6 hex nut. Rather than heat-pressing the nut, I adopted a structure where the nut drops directly into a hexagonal recess like a box wrench. By shaping it into an easy-to-grip hand lever, I made it possible to apply sufficient torque using only fingertip strength.<\/p>\n

      \n