It has been a while since I made a post on the new CoreXY 3D printer (tip: don’t start too many new projects at once). Lately I made some solid progress on it however, so I figured it was time for an update.
Since the last post, I have added the CoreXY gantry components and got all the X- and Y-axis motion fully working. Aside from some minor details, this part of the 3D printer is now complete and I am ready to move on to the next section.
In this post, I will show you the progress I made and share the details.
Main CoreXY motion components
Just like on the Z-axis, for the X- and Y-axis I also went with linear guide rails mounted to aluminium extrusion. A bit pricier than using linear rods, but the extra rigidity is worth it on a 3D printer this size.
For the Y-axis I used MGN12 linear guides mounted to the 3030 extrusion of the frame, but for the X-axis I chose smaller MGN9 guides mounted to 2020 extrusion instead. This was mostly done for weight saving reasons. All X-axis components move back and forth across the Y-axis. Less moving weight means that the 3D printer can print with higher speed/acceleration and prints end up with less ghosting/ringing artifacts.
The MGN9 rails also use smaller carriages than MGN12 rails, which meant I could design a more compact extruder carriage for the printer.
The guide rails themselves are nothing fancy, just budget rails from Robotdigg. Fixing minor issues on the rails by hand gave me more than good enough results on a budget.
On the X-axis I used two guide rails. With one rail, the extruder carriage was not mounted rigid enough. There was a bit of play in the carriage that caused an ever so slight radial rotation on the carriage. To prevent printing artifacts from that, I decided to add a second MGN9 rail on the rear of the 2020 extrusion and stop any unwanted movement.
The printer uses standard fiberglass reinforced 2mm GT2 belts, as I did not see any reason to use anything else. Steel core timing belts, for example, do not work well with the small pulley sizes that this 3D printer will use. Similarly, other belt pitches (3mm) do not offer benefits either. At least not for 3D printing purposes.
As for the belt paths, I went with two non-intersecting vertically stacked belts. This is different from my previous CoreXY 3D printer, that had the belts cross over.
This belt arrangement is similar to the belt path of the Voron 2. One difference is that with this arrangement there is no need for a belt tensioning mechanism. Here tightening the belts can be done by simply moving the stepper motors inwards.
To mount the motors I used 3D printed mounts and rubber vibration dampeners. I’m not entirely sure if the dampeners will be necessary. The NEMA17s that I use have 0.9 degree steps, are driven by 256 microstep stepper drivers and are mounted on a heavy, solid frame. That whole arrangement is not vibration-prone to begin with, and the dampeners might not make that much of a difference.
One way I do expect to benefit from the dampeners is from their temperature insulation properties. The stepper motors will get hot when the printer is enclosed. Having the dampeners in between the motors and the plastic mounts will help prevent the mounts from softening and deforming.
Because the stepper motors are not in direct contact with the frame, they are not grounded. Because of this, I made sure to add wires between the motor casings and the frame (which is grounded). This allows any built-up static charge from the motion of the belts to dissipate. Without it, static charge can start to arc over to the motor windings and cause problems.
To manage all the wires coming from the extruder, I used cable carriers/drag chains. I thought about using DIY tape measure cable chains, but those are too much of a hassle to use when regularly adding and removing cables. Plastic cable chains are a lot easier in that regard.
On the Y-axis I used a 10*15mm chain, and on the X-axis a 10*10mm one. The 10*10mm chain should be big enough for the wires that need to run through it (stepper, hotend heater, hotend sensor, IR sensor, fans). But if I want to add a second extruder at some point, I probably have to switch to a larger chain. I will cross that bridge when I get to it.
Cable chain bridge
To get the cables from the X cable chain to the Y cable chain, I added a 3D printed bridge. I spent quite some time on designing it, but I am happy with how it turned out. The style matches that of the chains and it blends in nicely.
It has a detachable cover for easy access to the inside.
Like many of the parts on this printer, it uses brass inserts for the threads. This lets it be taken apart and reassembled repeatedly without the threads wearing out (like what happens with plastic threads).
The back of the bridge also contains a discrete hole to route the X endstop wires through. Once again, keeping things clean and removing the need for cable ties.
What is next?
There are still a couple of minor things that I need to do to finish the X/Y components. Wiring up the endstops and routing the stepper motor wires, for example. I will do that after I build the extruder, because then I can do all wiring at once.