The cnc machine is now complete so I can explain what Ive done to turn a minimill into a working cnc mill. It will be fairly brief but youre welcome to email me and ask for more details.
First I bought one of these …
This is a SIEG X1 super micro mill mk2 from Axminster tools. Its built in china, its cast iron and its relatively cheap. It has its downsides like poor lead screws and nuts, and a slow spindle speed (2K rpm) but its good enough for me for now. So this will work as a nice stand alone desk mill cutting most materials, although I haven’t tried any steel yet.
Next you need some stepper motors. I bought 3 of these hybrid nema 23 stepper motors from motion control products.
The stepper motors need drivers to power them with 24v 2.5A so from the same place I bought these.
The drivers need step signals to amplify to the motors, so you need some kind of controller. I wanted to run everything off a small net book so it needed to be USB. There arent many USB controllers on the market. I went with the ncPod as it was recommended by a friend. Its still in beta and doesnt look like its full anticipated functionality will ever be realised, but the company were responsive and the board is a good price and everything it can currently do is more than enough for me.
None of this will work without power. I originally hacked a pc power supply, but it didnt supply enough volts (24 is best for these drivers) or enough current. This means the motors will only go slow when cutting or they’ll slip. The quicker you can run your machine the happier you will be. I eventually went with this supply from farnel. XP Power PSU 160W . To power the ncPod you will need a 5v switching regulator.
To attach the motors to the machine you need some kind of motor mount. You can buy kits from cnc fusion for the X1 but theyre expensive and you can make them easily yourself.
To make a mount you just need to rigidly attach the motor in line with each lead screw, and connect the shafts and lead screws with motor couplings. Couplings can be expensive so I went to ebay to save money. They were not the best quality but they work fine.
With all the mechanical stuff attached you need to wire the steppers, drivers and controller. Spec sheets should show you how to do this so I wont give the details. I used 4 pin xlr connectors on the box that houses all the electronics. It makes the cabling robust and looks more professional.
To talk to the ncpod, and make anything move you need some kind of cnc software. There are free examples available, typically on linux, but they wont work with a usb controller, so Im stuck with windows. Mach3 is a well developed free hobby come professional cnc tool that reads gcode and deals with all communication to the electronics. Its well worth the £100ish pounds… Mach3
Once you have Mach3 up and running you have to configure it for things such as the number of clicks per rotation which is determined by your motor resolution, screw pitch and microswitch resolution. You will also need to determine the maximum speed and acceleration for the motors. This is trial and error. I have my acceleration quite low to reduce the risk of the motors slipping. If you press tab when in Mach3 it provide you with a jogging window to move the motors or you can input gcode commands into the command line.
The final piece of software you need is to produce the gcode. For this I use CamBam. Its still in development but its already very good. You can define all your cutting paths and even do 3d profiles. I tend to not use the CAD functionality as I prefer AutoCad/SolidEdge but it will do most things.
So all thats left to do is CAD -> CamBam for gcode -> Mach3 to execute -> Watch your machine cut stuff!