Extensible CoreXY CNC Base

This model is the basic components needed to build a CoreXY machine that is designed to be customizable and built specific to a users needs. A primary benefit of CoreXY is minimizing moving mass, resulting in less energy needed to accelerate/decelerate the central carriage.

Demo

An example of this model used to build a pick-and-place machine can be seen below

Summary

A primary goal for this model was to allow the models to be agnostic to the actual dimensions of the machine, meaning that a user can build a machine of any size without needing to modify any of the printed components. There is also no assumption around a correlation in the length of individual axis, meaning each axis can be made exactly the size needed for a user's application. 

The frame of the machine is designed around 2020 aluminum extrusion. The brand or profile itself isn't particularly important, as long as it is standard sized 2020 aluminum extrusion. In the shopping list below is a link to 2020 extrusion available on Amazon, but any supplier should work. 

The frame is also designed around linear rails, with 4x rails needed for a complete build. Two linear rails are needed for the Y axis, one is needed for the X axis, and one is needed for the Z axis. For the X and the Y axis you should size your linear rail to the length of 2020 aluminum extrusion used for the corresponding axis. The Z axis is comprised solely of the linear rail, and thus its length will dictate the usable size of your Z axis. 

Printing

I suggest printing all parts in PETG with at least 2 perimeters and 20% infill. All parts are designed to be printed without a need for support material, or with basic tear-away supports - the central X carriage is the one component in particular that will require support material. These should also be treated more as guidelines and there is no reason you shouldn't have success with another filament type or print settings. 

Shopping list:

• Exterior Corner Bracket: https://link.amazon/B0hfwRSkd

• Interior Corner Bracket: https://link.amazon/B03BflYmZ

• 2020 extrusion: https://link.amazon/B09xxXHhi

• T-Nut: https://link.amazon/B018UxJ5y

• Rubber feet: https://link.amazon/B02IOAT1s

• GT2 toothed pulley: https://link.amazon/B03IYffCy

• GT2 idler pulley: https://link.amazon/B07L59JZZ

• Idler pins: https://link.amazon/B01HOjU1D

• GT2 belt: https://link.amazon/B059AKVOJ

• Linear rail: https://link.amazon/B0aBJS0BT

• Nema 17: https://link.amazon/B0a3PZ466

• M5 screws: https://link.amazon/B05OqH69q

• Limit Switches: https://link.amazon/B0eosf9QV

Assembly

Assembling the CoreXY machine is relatively straight forward. 

Step 1: Start by installing 2x of the GT2 idler pulleys into each of the corner pulley mounts, and inserting the idler pins to hold them in place. The idler pins may need a bit of force to insert based on the resolution of your prints, but once in should securely hold the pulleys in place while allowing them to freely spin
Step 2:  Locate both copies of the X-axis bracket, and install 2x of the GT2 idler pulley into each, again inserting the idler pin to hold them in place. Like with Step 1, a bit of force may be needed to insert the pins based on your prints but the pulleys should freely spin when fully assembled.
Step 3:  Attach your Y axis linear rails to your Y axis 2020 extrusion and you X axis linear rail to your X axis 202 extrusion using T-nuts, or your fastener of choice.
Step 4:  Build your complete chassis. Utilizing your 2020 extrusion, your exterior corner brackets around the bottom perimeter (printed or purchased) and your interior corner brackets along the top perimeter. Ensure that your 2x Y axis pieces of 2020 extrusion with the liner rails attached are assembled along the top of the frame with the linear rails facing inwards towards each other.
Step 5:  Attach the X-axis bracket to the slides on the Y-axis linear rails
Step 6:  Install the X-axis 2020 extrusion into the two X-axis brackets. Ensure that the linear rail is facing upwards
Step 7:  Install the Z-axis bracket onto the X-axis linear rail carriage.
Step 8:  Install the two 3D printed Z-axis end caps onto the linear rail
Step 9:  Install the Z-axis linear rail onto the Z-axis bracket
Step 10:  Install both of the motor brackets onto the back corners of your frame
Step 11:  Install all three of the Nema 17 stepper motors, making sure to keep the two on the back of the machine loosely attached for now.
Step 12:  Install the GT2 toothed pulleys onto each stepper motor. With the X/Y pressed all the way to the rear of the machine, you should ensure that the toothed portion of the pulleys aligns as close as possible with the idler pulley on the X bracket. One of the rear motors will need to have its GT2 toothed pulley installed "upside down".
Step 13:  Install the GT2 idler pulleys into the Z-axis bracket utilizing the idler pins as before.
Step 14:  Install the GT2 toothed pulley onto the Z-axis motor, ensuring the toothed portion of the pulley is aligned with the idler pulleys.
Step 15: Install the GT2 belts. The machine has 3x belts, 2 of them along the X/Y axis and the third controls the Z axis. The two belts on the X/Y axis run in their own plane. Start by inserting one end of the belt as far as you can into the groves of the 3D printed Z-axis carriage. Run the belt through the idler pulleys, the motors, and all the way through the machine back to the other side of the Z-axis carriage, where you will press it into the groves on the other size of the carriage. You will want to cut the belt so that there is not slack in it when installed, but it also should not be overly taught.
Step 16:  Now you may pull the two rear Nema 17 motors tight, thus tightening the belts. Tighten them down to keep the belts tight
Step 17: (optional) The prints do have mounts for limit switches if desired. The holes in the 3D printed parts should be sized to accommodate an M3 screwed directly into them. You may go ahead and install those now!
Step 18: We are done!

Using the machine

You may have noticed there was no mention of any sort of electronics or motor controller. This was entirely by design, as the controller chosen is really up to the application/user. If you are looking for suggestions, I would suggest exploring the FluidNC ecosystem as that is what I personally use and have found to be very easy to get setup and running. However, any electronics able to control 3x stepper motors should be able to run this machine - just make sure it has support for CoreXY control!

Onshape model:

https://cad.onshape.com/documents/28e57a0f789e46addee552c0/w/a354884c5e262041a97d668b/e/95219ccb73440c5b73c4f612?renderMode=0&uiState=6aadf365d03c4f1daef8ca87

Closing thoughts

If you do end up building a machine I would love to hear from you, both in terms of how it went and what you ended up using it for!