How I Designed Scalable CoreXY (v1)

Design Parameters and Requirements

This was the longest stage of this project and it was in the works for several months. I had to write down all my ideas, figure out what design parameters are important to me, what hardware and software I may need, what is this project really trying to accomplish.

This was the stage that I did a lot of research. This was also the stage that I decided that CoreXY movement mechanism is the best fit for what this printer needs to accomplish.

Knowing exactly what you are looking for helps in making key decisions. There are some other questions to answer as well, such as what is the budget for this project (not just money, but also time), and if the project is feasible. At this stage also it is important to decide what are the absolute must-have requirements, and what are “nice to have” features.

By the time this stage was done I only had a list of requirements, a lot of articles and background information on CoreXY, and some hand drawn sketches on what the machine may look like.

Find Supplies, Material, and Parts

In order to build anything you need to find out what material you have access to. I made a list of all needed material and tried to source all the parts first. From dismantling the old 3D printer I already had the stepper motors, control board, power supply and a few other bits and pieces. One of my design requirements was to have a larger print volume, so I needed much longer smooth rods.

At this stage I tried to find the needed parts first. The reason for this was that these parts may come in different shapes and sizes, made by different manufacturers, and may or may not be properly described. Availability and price was another big factor in my decision making. Many of the parts I ordered were not available locally from Canada and had to be imported. Some were substituted with other parts which changes some of the design parameters.

I think it was a good decision to make sure that I have all the parts and components before jumping into CAD software and start drawing. This helps to save a lot of headaches saved a lot of redundant work and potential need for patch-work.

Draw Everything, Build Your Ideas in 3D

Once all the components were ready then it was time to actually start designing the physical machine. I use DesignSpark Mechanical for most of my 3D CAD needs. The software is not perfect, but is free, and is relatively easy to use (and NOT web/cloud based so it does not depend on your internet connection either).

I started with drawing a model of all at hand components first. I created 3D models for stepper motors, extruders and hotends, PCB’s, 2020 Aluminum Extrudes, and all bearings and fasteners. This helps to move things around in the 3D model when designing. I actually design my parts right on the (3D model) of the actual components. This helps not only with visualizing the entire machine, but also making sure that everything is an exact fit and components will work together.

CoreXY
Taking time to model the components in 3D drawing helps in the design process by providing a more complete picture.
Idlers
Modeling the rods, belts, and bearings in the 3D drawing helps to ensure the design of the parts are accurate and they all fit together properly. It is important for the models to be accurate.
Carriage_back
Back of the carriage assembly, fan shroud stilling on top of PCB and wire-guides.

Experiment

New ideas came up at all stages of the development of this 3D Printer. Once I had enough components I decided to test a few things before moving on and finalizing. It turned out to be a very good idea.

For example I decided to test the strength of the stepper motor mounts. I had printed them using ABS and it turned out that the initial design was not strong enough. There were some flex in the ABS mounts that would have caused print quality issues. I ended up redesigning the mounts, and printed them using PLA that hold the motors in place very strongly.

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I also ended up redesigning and adding some parts to the z-axis lead-screw in order to ensure accuracy and to prevent unwanted vibration or movement.

Assembly, Firmware, and Fine-Tuning

It didn’t take too long to assemble the machine to a point that it was functional, however the firmware took several weeks to fine-tune and adjust. Since this was my first printer build from scratch I had to verify my calculations, and make sure that the firmware behaves as it should. Unfortunately I had many issues with Marlin firmware. According to my calculations all my values were correct, however some pins needed to be reassigned in the firmware that had me puzzled for a while.

WP_20160524_22_46_29_Rich

Even after I got Marlin tweaked to the point where it was seemingly working it started pausing in the middle of prints for no reason and was not performing well at all. I ended up switching to Repetier Firmware instead, which although is free, but is not open source. Repetier firmware worked flawlessly with the machine right off the bat without any issues.

Of course some tuning was still needed to achieve the best print quality. Some of the tuning was done in the slices and I decided to push as much of the parameters as possible into the firmware in order to simplify the software settings as much as possible.

This turned out to be quite a success.

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Tiny sheep against a 0.5mm pencil lead
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Dual extruder prints

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