XY Motion System | Why CroXY

A DIY tool changing 3D printer

There are many ways to move a printhead around a XY coordinate system, the most common kinematics are:

  • Bed slingers (Prusa Mk3, Voron Switchwire, Ender, and many more)
  • CoreXY (Voron 2.4, E3D Tool changer, and Many more)
  • Delta (Kossel, Flsun, and others)
  • Crossed Gantry (Ultimaker and annex engineering)
  • Simple Cartesian
  • H-Bot
  • Polar Scara
  • Rotary delta

I have choosen to go with the Crossed Gantry style kinematics. But why?

Why Crossed Gantry?

Most people familiar with 3d printers will recognize this motion platform from the ultimaker machines. I always admired ultimaker for the print quality they could produce, but at the same time thought their machines were hugely overpriced, and their close sourced/hard to mod mentality also don’t help my view on them, after all I like to tinker and mod stuff. I personally would never buy a ultimaker simply because I believe the same amount of money can be spend better elsewhere. The crossed gantry mechanism consists of 4 stationary smooth rods and two moving smooth rods. The two moving rods are then connected via two bearing/bushings on the print head(.

XY motion system of a Ultimaker Gen 3. Image origin from: https://all3dp.com/2/3d-printer-gantry-simply-explained/

Annex engineering and CroXY

Researching for this project I came across a open source design team called annex engineering. I never heard of them before, but they make some pretty impressive designs! Go check them out. I also found a machine called CroXY on GitHub

These two projects take on the crossed gantry mechanism (Lets call it CroXY – Brilliant name!) is much more elegant than ultimakers I think – mainly due to two design choices:

  • The first is, that they use linear rails instead of unsupported smooth rods for all motion. The unsupported smooth rods are not ideal because they can flex a lot in the middle of the travel. This especially becomes a issue for larger machines. Linear rails do not have this issue if they are properly installed on a good frame.


  • The second is that they got rid of the extra set of belts and pulleys and the long shaft that ultimaker uses to drive both ends of the moving gantry with one motor. Instead they just put a motor in each end of the moving gantry.
CroXY motion system. Image source: https://github.com/CroXY3D/CroXY

Pros and Cons of CroXY

While ultimakers method is undoubtedly the cheapest method and obviously good enough when well implemented, there are no doubts that the CroXY style is superior when you want to make larger machines and push the limits of acceleration. The CroXY design is far superior to any of the other common designs out there, the most popular ones being CoreXY and bedslingers. Here are some of the major benefits

  • Shortest possible belts any motion system can provide. Where CoreXY is one of, if not the, longest.


  • Only two toothed idlers pr Axis and no smooth idlers.


  • Increased torsional stiffness around what on a corexy is usually the x axis (the moving gantry) as there is a second perpendicular gantry providing torsional stiffness.


  • The second motor or axis means you basically double the possible acceleration before skipping steps – any motion system style could do this though.


  • No racking from unequal belt tension.


  • It looks awesome when it moves! Not downright badass as Deltas, but certainly more interesting than the old bedslinger or corexy 😛


All that being said. A properly designed CoreXY machine can perform more than good enough. Just take a look at what Simon Vez is doing with his VzBot:

That thing is crazy! But he is also using 4 motors on this design – Not a common thing to see on coreXY machines.

Of course CroXY is not just a dance on roses, there are three main disadvantages over let’s say a classic CoreXY when building a tool changing machine.

  • The motion system is twice as expensive. You need six rails instead of 3 and you need 4 motors instead of 2. You need 4 stepper drivers instead of 2 (do not do this with 2 motors on one driver as you will need to home then individually to avoid racking).


  • The machine has a bigger footprint compared to printable area due to the extra gantry.


  • The tool changing concept gets more complicated as one way or another the idle tools must be lifted when printing and lowered when changing tools. This is required to avoid collisions with the second gantry. This obviously adds complexity compared to a stationary tool rack like E3D, and everyone else uses on their CoreXY based tool changers.


So why CroXY? I do believe it is the ultimate motion platform for 3D printers due to the points listed above. And.. it looks cool!

Read more about

A DIY tool changing 3D Printer

Notify of

Inline Feedbacks
View all comments