CORE One Pins Mod (Gen 1, Gen 2)

While the 🥰 CORE One is an excellent printer with a well-designed stock system, this modification offers mechanical improvements for enthusiasts seeking enhanced precision and reliability. The Pins Mod inspired by the Voron community upgrades the XY gantry system by replacing the standard M3 bolts used for idler mounting with 3mm steel axles (pins).

Key Improvements - Eliminated Idler Play on the M3 bolts

- Smoother Operation that reduces potential vibration and mechanical noise

- Corrected Gen2 Motor Pulley Clearance: Restores the original GT2-style pulley clearance to prevent rubbing on the stock motor mount parts

- Toothed Idler Integration: Optimizes belt engagement using purpose-built toothed idlers (optional); reposition the idler to account for the different pitch-circle diameter and keep the belt path parallel

- Improved Reliability for the Belt Tensioner mechanism by using a heat set insert (optional)

GT 1.5 and the Gen 2 Upgrade: Do I still need this mod? 🤔

Yes 😎 and with the GT 1.5 / Gen 2 belt change, this mod is even more valuable. The GT 1.5 / Gen 2 upgrade improves the belt system, but it does not eliminate the radial play introduced by the stock M3 idler mounting bolts. The Pins Mod addresses that remaining weakness by replacing the bolts with precision steel pins, making the idler assembly more rigid, smoother, and more consistent. There is also a Gen2-specific fix: The new motor pulleys included in the Gen2 upgrade kit have a slightly larger outer diameter and can rub on the stock motor mount printed parts. This is corrected by restoring the same pulley clearance that was present with the GT2 pulleys. Thanks Dave for identifying and fixing this first. Give his model a 🧡 like as well!

Toothed Idler - How Many Teeth?

GT1.5 (Gen 2): - 1.5 GT 27T - Preferred choice

- 1.5 GT 26T - also a good choice

- 1.5 GT 21T - 🚫Not supported 🚫

- 👉 Requirements: 3mm inner bore (ID), max outer flange diameter (FD) ≤ 18mm

GT2 (Gen 1): - GT2 20T toothed idler with 3mm bore

- 👉 Requirements: 3mm inner bore (ID), max outer flange diameter (FD) ≤ 17mm

None of these choices change the belt path, because the pin positions in the XY carriage parts were adjusted to account for the different idler and belt geometry.

Idler Width & XY Carriage Compatibility

With the CORE One Gen 2 upgrade, things became much simpler: the commonly used POWGE toothed idlers come in the same 9mm width as the stock Prusa smooth idlers. To avoid confusion about which part to print, the 10mm variants of the XY Carriage were removed from the files section for Gen2. For the CORE One Gen 1, the XY Carriage is still available in two variants: 9mm for the stock Prusa smooth idlers, and 10mm for the Mellow toothed idler (see BOM).

I hesitated for quite some time whether to publish this model at all - not because it doesn't work, but because the build process requires time, patience, and the willingness to understand what you're doing rather than just following pictures. It's not overly difficult, but it is possible to mess it up! Personally, I would never build a CORE One without this modification, so I can only encourage you to consider going this route. I'll do my best to describe every detail of what you need to do and help you understand the reasoning behind each step. This will be somewhat lengthy, but it will help you get it done successfully. - If at any point you find a way that works better for you - do it your way!

- If you want to spend the time designing tools to help with idler alignment, please do so and share it with us! I've provided all the CAD resources to give you a quick start.

That being said, here's a time estimate: Plan around 90 minutes for reading, understanding, and building. You'll be rewarded with a beautifully play-free gantry system at virtually no extra cost - it's truly worth the effort 😎.

CORE One L user? The XY Motor Mounts for the Core One L require slightly different parts. Find these adapted mounts in the companion model: Core One L Pins Mod. All other parts and instructions are exactly the same, just print those two replacement parts.

Printed Parts XY Motor Mounts Modified to accept steel pins instead of M3 bolts for idler mounting, providing enhanced precision and reduced play.

XY Carriage Updated design to work with the new pin-based idler system. Available in two versions: - Standard version (9mm): Compatible with 9mm smooth idlers (stock configuration). Also to be used with toothed idlers with 9mm width for superior belt engagement.

- Modified version (10mm): Designed for 10mm toothed idlers for superior belt engagement

Belt Tensioner Pulley Redesigned to utilize steel pins with two variants available: - Standard version using M3 square nut

- Enhanced version with heat set insert for improved reliability

Press-In Tools Small tools to help you press in the pins without damaging the bearings or the printed parts. The tools are provided in 2 variants: - Smooth: Match the diameter of ths stock smooth idlers

- Toothed: A variant that match the toothed idlers

Assembly Printed-Parts Preparation