Desktop 3-Axis CNC Milling Machine
The Obstacles:
Below are the obstacles I overcame and the constraints I had to work around:
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Working with a constrained budget
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Which meant re-using old components from previous prototypes
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Meaning I had to use cheaper materials and components
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Access to only basic power and hand tools
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Which reduced my material selection to ones that I could work with based on my tools
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I had to design components to be simplistic and easy to manufacture (DFM)
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The Objective:
My objective was to follow the engineering design process to develop a 3-axis CNC machine capable of milling Aluminum.
To be successful, these were the design goals:
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Design & Build a frame rigid enough to have minimal deflection while milling Aluminum
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To create Linear stage motion actuator systems for each axis that have minimal deflection due to backlash
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To minimize deflection in the system from components deforming under load
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To reduce vibrations caused by milling
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To have a small footprint for portability and space savings
The Results:
In the end, I successfully made the CNC capable of milling aluminum! Below is a sample part I made to test the capabilities:
The Process:
Research:
With the various types of CNC configurations I looked into the advantages and disadvantages of common configurations:
Gantry Style CNC:
The gantry, which holds the spindle, moves over a fixed table. The X and Y axes are typically on the gantry, while the Z axis moves up and down.
Advantages:
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Large work area
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Fixed gantry design leads to great stability without a complex design
Disadvantages:
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Larger footprint
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A moving gantry leads to inertia-related issues
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A moving gantry leads to greater complexity and cost
Vertical CNC:
The table moves on the X and Y axes, and the spindle moves up and down (Z axis). The knee moves vertically to adjust the distance between the table and the spindle.
Advantages:
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Small footprint
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Widespread design
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Great visibility and access to workpiece and easier to set fixturing
Disadvantages:
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The knee structure can be less rigid when fully extended
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Also harder to manufacture with the current toolset
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Limited work area
Horizontal CNC:
The cutting tool is oriented horizontally. The horizontal design allows chips to fall away naturally and safely, which helps to achieve smooth, quality finishes
Advantages:
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Better chip evacuation
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The mass of the spindle and linear motion stages are closer to the base
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This leads to a more rigid design without increasing complexity
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Disadvantages:
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Limited vertical travel
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Larger footprint
Prototypes:
CNC 1.0
June 2021 - The true budget CNC
This version was a Gantry or router-style CNC, here I only used the material I had available such as wood, some steel flat bar, a DC motor from a grass trimmer and basic nuts & bolts. The only purchased components were 8mm guide rails, stepper motors and an Arduino with a CNC shield.
Overall the fundamental structure was ok but lacked rigidity due to the material selection, use of wood/self-tapping screws and use of not fully supported guide rails. In the end, the machine was able to cut through High-Density Poly Ethylene (HDPE)
CNC 2.0
March 2023 - The 3D-printed CNC
On the second version of my CNC, I went with a Vertical configuration with a moving bed and used a fixed gantry. With the fixed gantry it was easier to make a rigid frame to hold up the X & Z-axis. I purchased upgraded parts such as MGN12H Linear Rails, 2020 Aluminum extrusions, and a 500W DC Spindle for this prototype.
With the upgraded parts I designed a machine with a build volume twice as large as the previous version while maintaining a relatively rigid structure. The aluminum extrusions were coupled using 3D-printed components (All the white-coloured parts you see in the CAD model) made using PLA.
Unfortunately, before I was able to finish and test the machine all of the 3D printed parts warped after being left in the back of my car after attending a Reverse Career fair on campus, as a result, I chose not to re-print all the parts due to a couple of design errors I had made and the time and material needed to remake the parts.
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The printed parts that hold up the X & Z-axis were separated into three parts that stacked together but this caused some symmetry issues between the left and right side leading to the binding of the X-axis linear rails
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The Z & X-axis were quite heavy for the structure and would likely cause the fixed gantry to tilt forward from the cutting forces as also the brackets used to support the gantry were undersized for the task
CNC 3.0
July 2024 - The best one yet
After several renditions and countless hours of research and analysis of CNC designs, I created my best version using a horizontal CNC configuration.
The CNC 3.0 frame uses 2020 aluminum extrusion coupled with 3D-printed brackets made from PLA+ with increased wall thickness and infill levels to increase the rigidity of the plastic components.
With rigidity, precision and repeatability in mind, I'm using Linear rails on all three axes which all mount to their machined 6061 Aluminum bases which act as the workbed, spindle mount and foundation for the X-Axis respectively.
With the purchase of the new shiny and expensive components, I decided to re-use parts from the previous prototypes despite their respective drawbacks to maintain a relatively low budget.
The following parts were re-used:
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2020 Aluminum Extrusions
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NEMA 17 Stepper motors
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Arduino Uno + CNC shield
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500W DC Spindle
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Lead Screws
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Two sets of MGN12H Linear Rails
By using a horizontal configuration I was able to achieve something I struggled to do with the previous versions: Making a rigid enough vertical structure capable of holding up heavy X & Z-Axis while only using basic materials due to limited access to tools and materials.
The horizontal setup allows all that weight to sit nice and low and fully supported by the base/ground, this also helps with harmonics as now that mass isn't up high and swaying around during milling operations which in turn helps the quality of the milled parts.
CAD
The detailed CAD model was created in Siemens NX
Testing: CNC 3.0
2D G-code Test
As a part of the calibration process within GRBL, you need to specify the E-Steps (How many steps the motors need to take for 1mm of linear travel) for each axis.
I did this by telling the machine to move a specified distance and using a vernier caliper to measure how much it moved to fine-tune the E-step value.
I am running a simple 2D G-code file for a polygon to help check the E-steps for all the axes. I attached a marker to the spindle and applied tape on the workbed to draw out the polygon.
Performing a 2D G-code test with a marker to help validate the E-steps for each axis
The First Cut
The first cut on the 3-axis DIY CNC machine was exciting. After carefully setting up the machine and securing the aluminum workpiece, I manually ran the machine with a max cut depth of 1.5 mm. The endmill used was a 6mm 2 flute.
As the tool made contact with the aluminum, the sound of the cut confirmed that the machine was functioning correctly.
The surface finish was smooth with relatively minimal chatter, and the machine handled the operation well, validating the design and setup.