CORE One Mini - The Problem with the linear rails

While finalizing the XY motion system for the CORE One Mini, an issue came up with linear rail availability.

The distance between the linear rail holders is fixed at exactly 245 mm. The originally intended rail, a THK SRS12GN, is available in 220 mm and 245 mm lengths, while the more affordable and widely available MGN12H alternative comes in 210 mm and 250 mm. This puts the design in an awkward spot, as the shorter rails don't fully span the holders and the longer ones exceed the available space.


So, i've evaluated several solutions. 

Option 1: Cut a longer rail to length

The most straightforward option is to simply cut a longer rail down to size, typically to around 240 mm, using a cold cut saw. This results in a clean, mechanically optimal solution with no additional parts or design changes required. However, cutting hardened linear rails isn't something everyone can do safely or accurately, so while this works well for some builders, it's not universally accessible.

Option 2: Use printed end stops on a shorter rail

Another approach is to use a shorter rail, such as the 220 mm variant and prevent the carriage from sliding off by adding 3D-printed end brackets. This method is already used in commercial machines like the Bambu Lab H2 series, where the rail ends are capped rather than fully enclosed. In theory, this should work here as well, but it would require real-world testing to confirm reliability, especially under crash scenarios or long-term use.

Option 3: Modify holders and carriages

The third option for the current design, is to accommodate an up to 250 mm long rail by modifying the surrounding parts. Small cutouts are added to the linear rail holders and the XY carriages to allow the extra rail length to extend into these components. While this slightly reduces material in those areas, stiffness should remain well within acceptable limits. If live testing shows otherwise, the screw positions on the XY carriage can be moved outward slightly and the linear holder brackets can be redesigned as dedicated custom parts.

For the sake of simplicity, repeatability and ease of sourcing parts, the third approach has been selected. With this decision made, the critical elements of the CORE One Mini's XY motion system are now complete.

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For more background information on the project and an evolving FAQ, feel free to check out the main article, which will continue to be updated as the CORE One Mini progresses.

If you have any ideas, questions or remarks: feel free to drop me a line. Thanks again for being part of this and helping make the project possible - happy printing!

CORE One Mini - A Status Update and the Rocky Road to a Prototype.