PrintedBTU

PrintedBTU is a 3D printable ball transfer unit designed for custom trackballs and trackball modifications. The design is compatible with Bosch BTU dimensions for easy integration into existing projects and mounts.

The support balls are caged but remain loose inside the holder. The three screws act as both retention and a race for the top ball, helping ensure smooth operation.

Each BTU uses four ball bearings and three M2 countersunk screws while remaining fully printable on standard FDM printers.

The standard version should work for most users. Additional size variations are provided to account for printer tolerances and differences in M2 screw dimensions. Tighter versions may require additional tuning of screw tension. The loose version is designed so the ball is barely retained under normal use. The sizes don't change the ball recess, so let me know if it's not fitting so I can change it.

Hardware Required Per BTU

• 4x ball bearings

• 3x M2 countersunk screws

• 8–10 mm screw length

• 8 mm recommended

Printing Notes

• Tested in PLA and wood PLA

• Print at 0.2 mm layer height or finer

• 3 walls

• Change wall generator to Arachne

• Supports needed both tree auto and standard auto work

• Recommended painting of seams in screw holes, see photo

• Iron on top surfaces can help with smoothness in the recess

• Do not scale the model

Designed for custom peripherals, DIY input devices, and trackball projects. I use mine in a SvalBoard.

Assembly Instructions

1. Insert the three support ball bearings into the BTU body. Rotate them slightly if they do not drop into place easily.

   

   

2. Rotate the support balls so they are not aligned with the screw recesses. Install two M2 screws most of the way and hand tighten.

   

   

3. Place the top ball into the center of the BTU.

   

4. Install the final M2 screw and evenly tighten all screws by hand.

   

Notes

• Do not force the balls into the BTU, as scratching or damaging the balls can reduce smoothness.

• Do not overtighten screws.

• Some tuning can be done using screw tension.

• If excessive noise or bumps are felt during movement, slightly tightening the screws usually improves smoothness.

• Minor fitment adjustment may be required depending on printer tolerances.

• Smoothness may improve after a short break-in period.

Commercial licensing is available. Please contact me if you would like to use this design in commercial products, kits, or resale.

Pictured keyboard is a SvalBoard. The most comfortable keyboard ever.