Designing a 3D-Printed Hand-Tightened Collet-Style Ball Joint

2026-11-02

The arm joint built previously made it possible to firmly fix front-to-back folding and height adjustments using 10mm square pipes. However, with the base completely fixed, there was a lack of flexibility to pull the arm out diagonally or swing it left and right to match the layout of the workspace.

To use a USB microscope comfortably for PCB work, a joint is needed at the base of the arm that allows for a certain degree of tilting and rotation. While adding a commercially available metal ball head was an option, it would lengthen the connection part with the 10mm square pipe and reduce rigidity. Therefore, I decided to 3D-print a custom ball joint that could be directly connected to the base.

Concept of a Spherical Joint with Fine Angle Adjustment at the Base

The objective this time is to place a compact ball joint at the base of the arm, allowing the upright angle of the entire arm to be freely and finely adjusted according to the conditions of the workbench.

As a future expansion, I have a concept to attach a DIN quick-release shoe to this base section, developing it into a structure that can be attached and detached with a single touch to a tripod or clamp socket. Therefore, in this prototype, I will first focus on establishing a robust collet chuck mechanism that can reliably hold the ball.

Specifications of the Spherical Joint for Secure Hand-Tightened Locking

The goals set for the design are as follows:

• Holding Force Target: Secure sufficient friction to prevent the angle from slipping down during work, with the entire arm weight and microscope attached to the tip.
• Range of Motion Target: Secure a range of motion of approximately 50 degrees as an angle that can be moved smoothly without interference for adjusting the tilt at the arm base.
• Operability Target: Enable complete locking and releasing simply by hand-tightening the outer ring nut, without using any tools such as hex wrenches.

Design of the Collet Chuck Structure and 3D-Printed Ball

Using the CAD software FreeCAD, I designed and printed each component using PLA filament. The approach adopted to solve the challenges is as follows:

Collet Sleeve with Slits

I cut trapezoidal external threads on the outer periphery of the housing that holds the ball and created multiple deep vertical slits. By tightening the ring nut from the outside, the inner diameter shrinks uniformly as the slits narrow, adopting a collet chuck structure that wraps around the entire ball with uniform force. This efficiently converts high tightening torque into frictional force without concentrating excessive stress on a single point.

Integration of the 3D-Printed Ball and Square Pipe

The ball part to be gripped was also 3D-printed as a sphere. A shape that fits a 10mm square pipe was provided at the base of the ball, and it is fixed through with an M4 screw and nut. By modeling it as a single piece rather than repurposing a metal ball, both a strong connection with the pipe and appropriate clearance were achieved.

Thread Pitch Selection and Prototype Shape

The external threads were designed with a relatively coarse thread pitch to allow quick hand-tightening. Protrusions that are easy to grip by hand were provided on the ring nut side, ensuring that sufficient torque can be applied with just fingertip strength. Note that this prototype includes a wall-mounting flange (mounting tabs), which is a remnant of the initial wall-mounting assumption. Moving forward, I plan to improve this base shape and integrate it with the DIN quick-release shoe structure.