CorePen - 3D Printable EnerGel/G2 Pen

This pen is a clean, functional 3D‑printed body built around the Pentel EnerGel metal‑tip refill. It uses a screw‑down lower body, giving the pen a solid, mechanical feel and making it easy to service or swap refills. The overall geometry is simple and intentional: a straight, comfortable barrel with balanced proportions and a secure internal channel that holds the refill firmly in place.
 

Between the upper and lower body is a replaceable printed O‑ring that adds a controlled amount of resistance when capping the pen, giving the cap a more deliberate, premium feel without relying on overly tight tolerances. The O‑ring is easy to reprint or swap, but it shouldn’t be oversized — too much compression can cause the cap to bind or jam.
 

The pen is also designed to be modular. The grip section can be removed and replaced, and I’ll be releasing additional grip designs with different textures and profiles so you can customise the feel of the pen without reprinting the entire body. All future grips will remain compatible with this same upper and lower assembly.
 

This design may also be compatible with Pilot G2‑style refills. I don't have any on hand so can't test this yet. Let me know if they work!

Print Recommendations

This model requires good dimensional accuracy, especially around the threads and the long barrel. Treat it like a precision print.

• Layer height: 0.12–0.16 mm
• Walls: 4
• Infill: 20–30%
• Material: PLA, PETG, or ABS
• Supports: None
• Brim: 15-20 mm (strongly recommended)

Important notes:

• Ensure the bed is clean
• A larger brim greatly improves adhesion and prevents warping.
• If the thread feels too tight initially screw in slightly then reverse the thread a few times to work it in.
• If the cap feels too tight on first assembly, reprint the O‑ring in a different size rather than forcing it. (ID is 10.2mm and OD should be at least 12.8mm for those of you who want to make custom O-Rings