My CoreXY Printer build

Below are some pics and details of the printer I’ve built, mostly from Open Builds V slot. I’m not going to bore anyone with the full build log but here is a brief description and details of some of the more unusual features:-

It’s a Core XY design incorporating a Diamond hot end fed by three E3D Titan extruders. The hot end is slung between two 2020 horizontal rails forming the X axis. The frame is 600mm x 600mm x 1,000 mm with another 500mm added to the top to take the filament spools and additional extruder gantry. Build area is about 355mm in X by 340mm in Y and 760 mm in Z. The Y axis is two 4020 rails which also serve as the top frame members. The bed consists of two layers of rigid insulation, an 800W 240V silicone heater, a 400mm x 400mm x 10mm thick machined aluminium tooling plate topped with removable 6mm float glass. The bed moves in the Z direction, driven by three 8mm x 1mm pitch screws via a continuous belt and single motor. Separate V slot linear guides prevent and “wobble” or twisting. The extruders are mounted on a separate carriage which is passively moved by the man XY carriage which  enables me to use short (about 170 mm) Bowden tubes. Electronics are Duet Ethernet with the Duex5 expansion card.

Z rod thrust and ball bearings
Z rod to bed semi flexible coupling
Z motor / belt drive assembly
Underside of X carriage with “COB” LED light
XY gantry

I did try a single rail design with the hot end hanging over one side. It saved weight and increased the available X and Y travel but it wasn’t nearly so solid so I reverted back to a dual rail design.

Ycarriage assembly
Y Carriage

I designed my own case for the Duet plus Duex5 expansion board. There are two fans which blow air onto the back of the boards.  They are are controlled thermostatically – there is a post in my blog which gives more details and the enclosure is listed under “Published Designs” with a link to the files.

Duet Ethernet plus Duex5

The hot end nozzle itself acts as the bed probe. Here is how it works. Firstly the X carriage has 3 oil filled bronze bushes inserted – shown here:-

Bronze bushes inserted into upper X carriage

Then the Diamond hot end mount has 3 steel dowels which line up with bushes as shown here:-

hot end
Hot end mount with steel dowels

So when it’s fitted together it looks like this.

Hot end fitted
Hot end mounted onto X carriage

It’s rock solid in X and Y but free to move in Z. During testing I discovered that in may not always rise completely vertically when the tip of the hot end was pressed upwards. Sometimes one corner would lift more than the other two. So I decided to exploit that and fitted the two retaining springs that you can see, which clip onto lugs on the hot end end mount. I also reamed out the bronze bush that is furthest away and not visible in the picture, to create a bit more clearance for the dowel pin. This means that upwards pressure will always lift the furthest corner and that’s where I’ve fitted my homing switch.  You can just about make it out in this next picture

Metrol switch
Metrol positioning switch

This is the Metrol positioning switch that I’ve spoken about in my blog. It’s high accuracy with a claimed repeatability of 0.005mm. My initial intention was to fit it to the carriage so that the hot end mount would press down against it. Unfortunately it was too long and I’ve had to fit it the hot end mount instead, which means that whenever I change hot ends, I have use a screw driver for what is otherwise a tool free operation. Also, I have to reset the Z offset for the switch. Fortunately, the built in LED makes it easy to see when the switch is triggered or not, which makes fitting it a lot easier than it might otherwise be.

The switch is a normally open design but used in this way, with it being closed when the hot end is on it’s seat but open when it’s not effectively inverts the logic meaning that if it fails, it will fail safe (in as much as the bed could not crash into the hot end during homing).

Because the hot end is restrained on one side by the springs, it acts like a lever so any upwards movement of the hot end is amplified at the switch position meaning that I only need 0.2 to 0.4 mm or so of nozzle movement to trigger the switch. The switch trigger point is 0.3mm from the tip so careful setting of the switch could reduce teh Z offset even further but it’s not really necessary.

This next picture shows the fully assembled hot end. Note that the Bowden tubes are under compression which also helps to keep the hot end pressed down on its seat but I’ll cover the extruder mounts later.

fully assambled hot end
Fully assembled hot end

In the above picture you can see one of the two print cooling fans. These blow air through ducts in the lower X carriage which directs the flow downwards onto the printed part and away from the nozzle. It’s difficult to photograph especially with my penchant for making all my parts in black filament (E3D Edge PETG by the way) but here is an openscad image.

Openscad image of X undercarriage with fan ducts

The final thing that readers might be interested in how I’ve chosen to mount the three (E3D Titan) extruders. With a bed that is 400mm x 400mm in a frame that is 600mm x 600mm and the extruders fixed to the frame, I calculated that I’d need Bowden tubes about 1,000mm long to reach all the corners. So I wanted to find a way that would reduce this length. Initially, I had them suspended above the bed with a counter weight and pulley arrangement. This was OK(ish) bit not very elegant. My latest design iteration is to mount them on there own XY gantry, above the main carriage. Initially, I thought about using a second set of motors and belts but discounted that on the grounds of complexity.  my calculations also suggested that despite the increased mass, my existing motors would be sufficiently powerful so the extruder carriage is passively driven. That is to say, it is “dragged around” by cords (actually 7/02 cable) attached to the X carriage. This also effectively gives some degree of decoupling which means that for small zig zag infill moves and holes, the extruder carriage is more or less static.

Here is how it looks:-

Extruder Carriage Front View
Extruder Carriage Rear View
Complete Extruder Axes Assembly

I also took the opportunity to tidy up the wring which previously came down from the top through flexible conduit, by installing a cable chain. From the above picture, you can see how the Bowden tubes are kept in compression by being slightly longer than is necessary.

Finally, here it is in action. Print was set to 60mm/sec, with non print moves set to 350mm/sec. Acceleration set to 1,200 mm/sec^2 for X and 660mm/sec^2 for Y.