Open box CoreXY upgrades

After seeing a few CoreXY reviews on youtube, I desired to get one to play with. I spotted an open box Coreception 300 sold by SainSmart. I ordered it and expected it to need some work, but that is what brings me joy. It came in a well worn box, but was complete and undamaged.

I cleaned, lubricated and inspected while assembling. I imagined upgrades, feeling uncertain about hot end with titan extruder over top. I wanted to try it first in stock form. In about 4 hours, it was printing.

I ordered a Biqu H2 500C extruder. I found H2 could be installed, with stock nozzle position retained. I weighed parts, and found 300 grams of weight reduction. No loss of build volume. That is huge! It was necessary to open mount bracket, and fabricate a simple aluminum plate for mounting

I found extruder direction needed to be inverted, and steps increased to 932. While controller was same MKS Robin Nano V1.2 as two of my other printers, it had custom firmware, and could not be changed by menu settings. I used Marlin M92 command to set E step, and with inversion. While that seemed to work for testing, machine became irrational. I found reloading firmware fixed issues, and config.txt was used to make changes.

There are a few similar printers: Creativity ELF, Koonovo Elf, TwoTrees Sapphire Pro with Robin Nano V1.2 controllers. I found Creativity has upgraded firmware. I have completed configurations for Marlin V2.1.1, and it compiled, but have not tested yet.

More upgrades in process, will do another post for that.


While the printer has many nice bones, it needs attention in Z axis stability to make it better. Here are a couple mechanical changes.

Original design has two end stops, but they are not adjustable. Bed springs needed to be nearly 100% compressed to keep nozzle off build plate. I found many comments about this in searches.

Limit switch boards were removed, and open area was traced with a pencil to identify area to add adjustment screw. Holes were drilled and tapped for screws, and lock nut installed underneath.

Gusset plates were purchased and installed to reinforce Z axis top mount extrusions to box frame. Without plates, extrusions rotate slightly, upsetting stationary limit switch position.

Stepper couplers were rubbing on lower Z axis mounts, prior to my purchase. Video assembly showed using wrench as spacer for leaving gap. Evidently this did not happen. Spiral couplers compress with vertical load. Load also presses on stepper shaft, thrust load is not desirable for stepper motor life.

Using ball thrust washers, decouples stepper, and solid coupler will not result in Z shift. A lathe was used to inset upper race to coupler bottom for allignment. Show is original worn spiral coupler. Lots of wear for what looked like one partial print, based on residual left on build plate.



3D printing helped in upgrade process. Belt idler pulleys were roughly manufactured, showing belt material stuck in some teeth. I ordered standard idler pulleys for replacement. Pulleys adjacent to print head on X axis had hubs of smaller OD. Without reducing, print volume would need to be reduced, and X endt stop changed. If pulleys could be put in lathe chuck, they could be easily cut down. FreeCad was used to make cylinders to hold, center, and provide reference for desired OD. Cylinders also protected bearings.

Picture shows origin small OD pulley. Note it has wear marks on top. Screws were over tight, binding pulley rotation. Shown on top of standard pulley is a black teflon 0.5mm shim washer. I plan to these to shim pulleys from mounts. They are for RC hobby cars.

I also plan to replace M5 threaded screws with 5mm shoulder screws for pulley axles. Threaded M5 screw has an OD of about 4.87mm, not good for mate to bearing ID of 5mm. It might be possible to purchase long, partially threaded screws, and cut them down. Or fabricate custom screws.


Parts were printed for 45 degree spool mount, and masts for print head cable. CoreXY printing seems to need these parts.


I took a leap of faith, and installed MKS Robin Nano35 V2.0.3.6 firmware, replacing original firmware. It provides more features, and is same as MKS R-N V1.2 board purchased for firmware development bench testing. It is configurable via menu, but I modified RNconfig.txt for correct defaults. It all worked first time!

I am building confidence for testing Marlin 2.1.1 build.


Have you looked into Klipper?

I looked into it some, seems simple on printer side, but secondary PC, or pi adds complexity. I want to try Marlin first, it might satisfy my needs.

I am comfortable with embedded systems, significant development work with automotive ECUs.

It really is not complicated. The biggest thing is the use of a parameter file for virtually all values that have to be compiled into Marlin firmware. Edit the printer.cfg file, restart Klipper, and you’re in business with the new values – no recompiling & reflashing required. It’s very liberating. In addition, it has built in support for resonance mitigation and Pressure Advance, which calibrates to produce sharp corners.

I print in remote workshop without network. Stand-alone operation is important feature.

That would be somewhat more involved, but certainly do-able. Give the Pi an IP address & you could connect to it using a tablet, phone, etc. All you need is a browser.

I have a spare Pi, and Pi400. I might try Klipper to check it out.

I have concerns about real-time events, involving endstops temperature controls, pressure advance… I assume they are handled by printer controller in safe way, regardless of com link activity. Activity split between embedded real-time uC, network, micro processor w/OS … is complicated.

I found android app called 3DFox, it is handy to connect to printers via USB. It has pronterface capability, and can launch prints located on tablet, or index files from printer SD. It works on my phone too. Great for trouble shooting and setup.

With Klipper, the controller board (MCU) in the printer is basically lobotomized. It’s functions are turned over the to Pi. The only thing running on the MCU is a small firmware that just carries out instructions from the Pi. The Pi is a much more capable platform than the MCU, so things like real-time events are handled better. The web interfaces for Klipper include an Emergency Stop button on the Daskboard that will stop printer activity immediately.

I will give Klipper a try, this winter.

Having a wireless E-stop on a network, reminds me of IT guy saying, “if you experience network issues, send me an email”. :slight_smile:

They’re not really the same thing. In your example, the remedy is likely impossible. In the Klipper case, it is highly unlikely that it would be impossible. Remember, Klipper is running on the Raspberry Pi, not on the computer that’s used to administer Klipper. The Pi is directly connected to the printer, normally via USB, so it is very close to the printer.
Yes, the link between the Pi and the computer is on the LAN, but it is simply a web browser on the admin computer. And, any computer on the LAN can be used to administer the Pi. It is even possible to have multiple computers connected to the Pi.
Also, the link isn’t necessarily wireless. Both the Pi and the admin computer can be hardwired to the network.
Don’t forget, some printers have a reset switch that can be used to immediately stop all printer activity. And, if necessary, there is also the power switch, or the power cord can be pulled.
So, bottom line. using Klipper doesn’t really reduce safety. In fact, it increases it, because it adds extra safety possibilities to those that are always available.
I’m not sure what you mean by

I assume they are handled by printer controller in safe way, regardless of com link activity.
but I suspect you are giving the onboard MicroController Unit (MCU) more credit than it deserves. The MCU has a limited number of sensors. There are many events that can happen that the MCU cannot even detect, never mind do anything about them.
For example, say the filament being extruded gets jammed up around the nozzle and overheats, leading to a fire. The MCU cannot detect this. Don’t be alarmed though. The odds of this are very very low. In the past there were fires caused by 3D printers, but I haven’t heard of any in the entire time I’m been 3D printing. Those fires were mostly caused by runaway nozzle heating. It was known as “thermal runaway”. That issue was addressed a number of years ago by improvements in firmware. That is, if the thermistor in the heater block does not provide data in the manner expected by the firmware, the firmware shuts things down.
So, what are the safety recommendations? Virtually everyone I’ve conversed with recommends having a fire extinguisher in a location where it can be quickly employed to put out a printer fire. This is particularly true for enclosed printers, because they tend to operate at higher temperatures. I have seen a number of setups where a smoke/fire detector has been installed inside an enclosure. And, it is recommended to have a smoke/fire detector near the printer(s). I have one 4 feet from my printers.

I’m stoic. :slight_smile:

I printed a quilting template for my wife. She designed outline on paper. I used FreeCAD, and deleted material for less filament. Circles are to place special nonslip pads. A rotary cutter will be used to cut material.
Diamond is about 317 mm long, 2mm thick. It took about 1.5 hours to print at 80% infill. Sides were smooth with no sign of elephants foot.