Desktop CNC Mill Conversion

I've begun machining a part which will replace the indicator knob with a toothed pulley on the mill. I am using a piece of steel that was used as a counterbalance weight in an x-ray machine as my source material.  I could glue the toothed pulley in place of the indicator wheel, but then I would not be able to use it as a manual machine. I prefer to keep that capability in case I have computer issues or some other failure causing it to not work. Then I can still make parts on it.

I've been a bit behind on documenting stuff. I've uploaded a few pictures. Here is a quick summary with some info about a few of the pictures:

The first picture is the mill I am going to modify. It is a Model T-981 from Central Machinery. It probably came from Harbor Freight, but I bought it used. It was made in 1988. Still runs well and just needed a few minor adjustments. I went with this over a Bridgeport due to price and because it's a nice size for hobby work.

The second picture is my test setup for the motor. The machine I salvaged most of the parts from had 10 steppers along with 10 drivers and a nice power supply. I cut the stepper chips off of the main board with a Dremel tool. I then just soldered the wires directly on the pins of the controller while it is still on the PCB. This provides me with a decent heat sink and keeps everything together nicely. All of the motors also have connectors on them so it is easy to take things apart as needed for wire routing later on. I drove it with a cheap digital signal generator. The stepper driver was very easy to work with. Just needed to hook the motor up to it, give it power, and a couple resistors to set max current of the motor.

Other pictures show a closeup of the stepper with driver, box of motors belts and toothed pulleys from the CR reader I stripped down, and the board that I cut 4 of the driver ICs off of.

The mill uses a set of pulleys to set the speed. Normally you would look at a chart showing speeds and what setting to set the pulley to. The problem I ran into was that I did not have the owner's manual to the mill. The mill was made quite a few years ago and this version is no longer produced. I could not find an owner's manual online because of this. A tachometer would be an easy way to see what speed it is running at, but I didn't have one and didn't want to spend money on something I will only use once.

My solution was to tape a couple magnets onto the end of a drill bit. I used two--one on each side so it would be somewhat balanced. I then wrapped electrical tape around it to make sure they would stay on. To make the sensor I wound some wire around an allen wrench. I attached the leads to an oscilloscope and measured the waveform to determine the speed it was rotating at. Then I recorded the speed and what pulley setting it was on.

So far I am off to a good start. I have salvaged all the power supply, motors, drivers, belts, pulleys, and metal I will need. I still need to find some optoisolators to go in between the computer and the driver IC. 

I don't want to make any permanent modifications to my mill. That way I can still use it to make parts. So my first step is to begin machining a new part that holds the toothed pulleys onto the shaft of the lead screws.