Design and Manufacturing Principles
This machine was designed as a versatile tool capable of performing most small machining tasks typically encountered in a small amateur or professional workshop. It fits well in a compact workshop or laboratory.
Structure and Kinematics
I opted against a router-style structure because it is less rigid and significantly harder to calibrate. The classic structure of conventional milling machines (XY+Z) offers several advantages compared to a router structure (Y+XZ). First, the X and Y axes are interconnected, making it much easier to adjust their perpendicularity. The X and Y rail planes are naturally parallel. Second, and more importantly, the classic structure has fewer degrees of freedom, meaning fewer adjustments are required.
Additionally, each adjustment affects only one axis at a time. On a router, adjusting the Y-axis can disrupt the Z-axis, making the calibration process more complex and requiring more tools.
During the design phase, I focused on ensuring the machine could be finely and easily adjusted by following these principles:
- Minimize joints and the number of parts, avoiding components like angle brackets.
- Avoid thickness adjustments (e.g., no shims); all adjustments are rotational.
- Contact surfaces influencing kinematics are never machined surfaces, as no cutting process at my disposal guarantees perfect perpendicularity or parallelism.
First version
Rigidity
The entire structure is oversized for enhanced rigidity. I used 20mm-thick plates and heavy-duty aluminum profiles designed for structural applications. For instance, the head profile measures 80x160mm and weighs 2kg on its own. The entire structure is assembled using 8mm screws, allowing for secure clamping.
Detailed adjustment instructions will be provided.
Manufacturing
I assembled this milling machine with minimal tooling:
- A drill press.
- A ruler, compass, and carbide scribers.
- An angle grinder to size the linear guide rails.
- Pre-cut and dimensioned aluminum profiles and plates.
- A dial gauge with a stand for assembly and calibration.
Compactness and Work Area
Routers typically offer a larger work area compared to the classic structure. To maximize the working area, I did not use standard bearing blocks for the SFU1204 ball screws:
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The assembly is reversed compared to the recommended setup: the fixed bearing block is placed opposite the motor, and there is no floating bearing.
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The fixed bearing journal is reduced from 10mm to 8mm.
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This means the ball screw is not a standard SFU, but it is still relatively easy to source.
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Standard SFU screws can be used, but this would require adapting the design and accepting either a larger machine or a reduced travel range.
Specifications
- Footprint: 500x500x500mm
- Work area: 250x150x150mm
- Linear guides: 4x HGR15 on all three axes
- Motors: NEMA 22, 1.8Nm or 1.2Nm closed-loop
- Controller: FluidNC with CNCjs on a Raspberry Pi
- Speed: At least 4000mm/min
- Verified machining capacity: 1mm cuts with a 6mm end mill, achieving 0.01mm precision with the current spindle.
Very nice design and writeup!
What is the total weight of the machine? And approximate cost of components?
From what I can see, it still needs a few more features. Dials on the hand wheels, pause/resume buttons, and individual enable/disable switches for each stepper motor (or can that be done from the LCD?). It is very useful to be able to e.g. pause and switch off Z stepper, pull the tool up out of a hole and clean out chips/apply lubricant, and then put it back down exactly where it was and resume. Or manually operate Z with precision for drilling holes. I only do shallow drilling with CNC due to the unpredictability of chip jamming.
Is the spindle electrically isolated from the bed? I don't know how I could live if mine wasn't, because I use electrical contact for probing, for zeroing Z after each tool change, and with a rod in the spindle for centering on internal or external features. I also have an LED connected to the spindle so it lights up when contact is made for manual operation.
I also recommend protecting the Y rails from chips. My covers are just sheets of typing paper coated with box tape, and stuck to the machine with blue masking tape. Surprisingly effective. It does hang over the Y knob annoyingly when moved forward, but not really a big deal.