Mike's Workshop Notebook

CNC Mill Conversion

Some time ago, I acquired a set of servo motors and drives. While stepper motors are capable of performing well in many CNC applications, servos offer clear advantages in smoothness, accuracy, and overall reliability. Having the servo system on hand provided the motivation to move forward with a CNC mill conversion.

Photos

CNC Mill Pic
I used a Precision Matthews benchtop mill as the foundation for my CNC conversion.
CNC Mill Pic
A complete ball screw kit was purchased for the X, Y, and Z axes. The conversion kit included motor mounts, but they were not compatible with the servo motors I had on hand. As a result, I machined a new set of mounts to suit the servo installation.
CNC Mill Pic
The mill was disassembled to replace the acme screws with ball screws, improving precision and reducing backlash.
CNC Mill Pic
An oil pump was added to provide lubrication for the ball screws. Due to the varying distances between axes—and the vertical orientation of the Z axis in particular—oil distribution is not uniform. When the Z axis receives the proper amount of oil, the X and Y axes tend to receive an excess. To address this, a flow-control manifold with needle valves will be added to regulate and balance the oil flow to each lubrication point.
Manifold
Flow-control manifold with needle valves used to balance oil flow to each lubrication point.
CNC Mill Pic
The highlighted section shows the spindle speed control board. The rectangular component wrapped in black electrical tape is its dedicated power supply, clearly engineered to the highest “shop prototype” standards.

To power the supply, 110V AC was routed into the enclosure. Fortunately, the board itself draws only a few milliamps at 12V DC, so the electrical demand is minimal, even if the presence of line voltage in a tight space adds a bit of excitement.

Space inside the spindle control box was extremely limited, but with some careful positioning, creative packing, and a bit of persuasion, everything fit. Just barely.

CNC Mill Pic
Limit switches were installed on all three axes. In addition to preventing over-travel, they provide a repeatable home position for the controller. Travel in the opposite direction is managed through software-defined limits.

For the mounting hardware, I used an online fabrication service (SendCutSend.com). They offer cutting, bending, drilling, and optional finishing of aluminum parts from a supplied STL file. The parts were very affordable, and the turnaround time was impressively fast- much faster than I could have made them myself.

CNC Mill Pic
Interior view of the enclosure showing the motor power, control, and drive components.
CNC Mill Pic
The Motor power section. From top to bottom: Contactors, EMI filters, and motor drives. The control board power supply is mounted on the side wall.
CNC Mill Pic.
The control electronics are arranged in three primary sections. At the top is a digital input/output board used to control auxiliary functions such as coolant pumps, monitor limit switches, and provide an analog output for spindle speed control. Below that is the main processor control board. I selected the Acorn CNC control board from Centroid, which offers a good balance of capability, affordability, and solid documentation. At the bottom is an interface connection board. Rather than hardwiring all connections, I chose a modular approach to allow for easier maintenance, component replacement, and future modifications. In practice, the number of required connections—particularly from the spindle drive and limit switches—was greater than anticipated. Hence the funky, congested layout.
CNC Mill Pic
The all important, "Oh Sh*t!" Emergency Stop Button with system power switches and indicators. (BTW, The emergency button works great!)