So you want to CNC?

[Jerry]

CNC is exploding in the home shop arena thanks to cheap control software like Mach3 and EMC2 and cheap motion control solutions like the newer servo motor drives.

Ill say this right off. I do not believe in stepper motors for machine tools. They are slow and noisy and open loop. You never know if something happened and you lost a step someplace. Many people counter that if the machine is properly tune this wont happen. It not something I want to risk. About the only commerical company that ever used steppers on a machine tool was Bridgeport on their Boss series mills. They stopped when they wanted sub .001" resolution.

Here is a site that has done a comparison review of different non-commercial servo drives out there: http://www.thecubestudio.com/ServoDriveReview.htm

So you want to go CNC, whats the best way?

The best is to buy a working machine. You would be surprised how cheap a 20 year old CNC machine will go for. And there is still support for some of the older controls especially if you get something like a Milltronics control. With this option you are ready to go. Buy tooling and tool holders and start making parts.

Next best is buying a machine with a dead control. A machine with a dead control can be bought near or at scrap prices. CNC machines cannot be used manually without a control so when the control goes it becomes a boat anchor. From here you can go one of two ways:

Commercial Control: There are several companies that manufacture controls to replace the dead controls on machines. Centroid, Ajax, and Milltronics are a few of the companies out there. Some options will allow you to keep your existing drives assuming they still work, other packages will replace everything. Given what I have learned about CNC machines this is the route I would go if I ever do another machine.

Non Commerical Control: There are primarily two software packages out there that people build machines around. Mach3 and EMC2. Both allow you to use generic PC hardware to run a CNC machine.

Mach3 is probably the most popular package in the world, is easy to use and has great support. It has its own forums as well as a Yahoo Group to offer support and they are both very active. Updates and development are continuos. ~$179. Free version will run about 200 lines of code in mill mode.

EMC2 was started by NIST and runs under Linux. It is free. It actually has some features Mach3 does not like Rigid Tap and closed loop feedback. But you pay for it in its user-unfriendlyness.

Using these two seem cheap but the get expensive fast. First you have a computer, then a breakout board for the parallel port, then drives and motors. You usually cant use your old servo drives since they use analog input and you need digital input. Rutex makes a Step/Dir to analog converter board and well as YAPSC:10V, a open source version. There are also external motion controllers like Servo2Go, DSPMC, and a few others that will talk to Mach and EMC and control -10-+10v analog drives common in CNC machines.

Next option is to convert a manual machine into CNC. This is even more involved. You now need to acquire and install ball screws, motor mounts and all sorts of stuff like electrical cabinets. You also kill the value of the machine when you do this. A bridgeport converted to CNC is worth significantly less than a stock manual machine. Once the machine has ball screws the machine is not really usable manually. Do to the low coefficient of friction for the ball screws the cutter can grab and back drive the screws.

Last is build you own machine, Done it, will never do it again. Now you are designing everything. And if you think you know better than the big guys (And I have seen many who think they do) then you are nuts.

I have built or retrofitted 5 machines now. Here are some build logs of two of mine:

http://www.cnczone.com/forums/showthread.php?t=28668

http://www.cnczone.com/forums/showthread.php?t=85349