Kit Review: Mini Mill CNC Conversion

Instructions on Make: Projects

What do you do when you want a CNC machine but don’t have the room or the funds for the massive professional equipment needed to cut custom parts? I found myself with this dilemma, so I chose to scale down my purchase and invest in a manual mill that I could eventually convert to a CNC. Before purchasing my Mini Mill from, I did some research to investigate what it would take to switch from a manual mill to a complete 3-axis “Computer Numerically Controlled” machine. Many of the popular small hobbyist mills are manufactured in China and Taiwan and then shipped to companies like Harbor Freight, Grizzly, SIEGE and Micro-Mark who paint them various colors and sell them under different names. Since these mills are all based on the same design, a community has formed around this popular mini mill platform to share ideas, hacks, and improvements through forums and a wiki . When opting to convert to CNC, there are numerous kits and conversion designs to choose from that span simple PDFs and wiring diagrams to high precision hardware and ready to run electronics bundles.

CNC Fusion is a small company that machines high quality conversion parts made from 6061 aluminum for small mills and lathes. The company started in 2004 when Michael Rodgers, a machinist by trade, wanted to create a CNC machine but realized that he could not build the parts he designed without first owning a CNC machine. That initial desire has led Michael to design and fabricate CNC conversion kits for small manual mills and lathes, and now his kits are sold around the globe (40% of CNC Fusion production is shipped to overseas customers). The household garage has been converted into a machine shop where Michael machines the majority of the kit components using a large 3 axis SHARP machining center while wife Shelley helps run the large Okuma CNC lathe to machine the ends of the ball screw threads sold with their kits.

With the X2 Mini-Mill CNC kit #2 all the new upgrade parts bolt to existing features and you replace the factory lead screw with high precision ball screws and new motor mount adapters to accept NEMA 23 stepper motors. The hardware installation is very straight forward and requires the disassembly of the X and Y axes before reinstalling the ball screws. The only physical modification to the mill occurs during the installation of the Z axis motor mount, and requires that you drill two 1/4″ holes into the column of the mill. Besides this step, the entire process is completely reversible in case you ever decide to switch back to manual machining (but honestly why would you!)

The electronics are sold separately, but Michael suggested I source the driver board and stepper motors from the company Probotix who offers complete electronics bundle kits for three and four axis machines with a special package designed specifically to fit the X2 Mini Mill. I opted for the Ready to Run electronics bundle which will cost an extra $150 but includes all the additional components that you will need to get your kit operational. (option includes large electronics enclosure, fuses, fans and necessary wires, nuts, bolts…)

I had saved an old Thinkpad laptop just for this project which happened to have a parallel port on the back. If your computer does not have a parallel port, Probotix offers a USB breakout board for an additional $75. I decided to stick with the parallel port connection, but upgraded to the PBX-RF breakout board. This breakout board was designed for hobby CNC machines, and protects the 5V logic portion of the board from the 120V side to ensure that your electronics will not fry if you get a spike or a short circuit from the motor drivers. An added safety feature well worth the initial cost.

A note about using laptops to run the CNC control software from Len at Probotix:

Some years ago they started putting advanced power management features into the bios whose primary purpose seems to be to extend the life of the battery. The problem is that because it runs in bios (under the operating system) it has higher priority than anything the OS is doing. If the bios decides to, for example, check the fan speed while EMC2 needs to be sending a step pulse, it will throw a hiccup into the pulse stream and stall the motors. You may or may not be able to disable this in the bios – even if the bios has that option, the issue may not completely go away. There is a short blurb about it here, and some more info here, and here.

So, before you run out and purchase a new laptop to run your CNC machine, you might want to think about sourcing an old desktop for cheap instead. I have been able to use my Thinkpad to run Mach3, however, I had to Optimize Windows for use with Mach3 following these instructions.

Probotix also offers the RBX-1 3-Channel Opto-Isolated Relay Board which I added to the package. With this board you can turn power on/off to three devices rated for 12Amp at 125VAC. For example, you could control power to the spindle, coolant pump, and vacuum system all from your CNC control program. Note however, the relay cannot control the spindle speed but only turns power on/off. This could be used as a safety feature to automatically turn off power to the spindle while you clamp down your work piece or remove a finished part from the machine.

When my kit arrived, I simply connected the stepper motors to the X,Y, and Z ports on the back of the electronics box, plugged in the power cables, and attached the parallel port serial-port to the laptop. With the electronics connected, I then installed and configured the CNC control software to communicate with the machine. Probotix recommends the free Linux-based EMC2 software package, but the kit will work with other CNC control software including MACH3. You can find example settings for both EMC2 and MACH3 on Probotix’s Support web page.

3-Axis wiring diagram from Probotix

With both of these kits installed, the last step is to fine tune the machine and install any limit switches and emergency stop buttons. Limit switches are not included with the electronics kit, but are not required to run the CNC machine. They are an added safety feature however, and will inevitable prevent you from crashing the machine if you are new to CNC. With everything installed and running it is finally time to design a test part using a CAD program, import the file into a CAM program to generate G-Code, open that file in your CNC control software, secure the metal stock to the table, then run a test cut. Assuming everything was done correctly, you should now be able to design and machine your own custom parts.

Both CNC Fusion and Probotix have great customer support and are very friendly and helpful. I am very impressed with the quality of each of the kits and was amazed at how easy it was to install the hardware components. If you are not comfortable working with electronics, the Ready to Run electronics kit saves time and anxiety. I was able to install the hardware conversion kit and make the first test cut in the same day. The real trick with all of this is learning to use the different CAD, CAM, and CNC controller software packages, and this is where people who are new to CNC may struggle. I am currently working on a tutorial that will show how I hooked up my limit switches and configured Mach3 to run on my computer.

For instructions and images showing the installation of the CNC Fusion X2 conversion kit, go to the CNC Mini Mill Conversion Kit (Hardware) page or go to the CNC section of Make Projects with more CNC related tutorials coming in the future.

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