I've been contemplating building a CNC router for years. I work in the woodworking machinery business and attend shows across the country several times a year. I ask a lot of questions to the CNC guys at thermwood, komo, and biesse and have even read susnjara's book about cnc routers.

BUT......

Most of this information is far beyond my capacity right now. I need technical help with actually getting this stuff to work. I really have no idea where to start. I'm willing to spend a little money to experiment, but nothing helps more than just talking to plain ole' folks in person, and seeing projects that they have.

So I would really like help locally if someone is willing to help me learn with their knowledge of the internal workings. And if someone could help me find some basic starter info on how the electronic portion of these machines work it would be a great help.

I am a programmer by education, a woodworking machinery marketing manager by trade.

Im in Amite, LA ... that's about 30 miles east of baton rouge and 50 miles north of new orleans.

OK, you asked about the internal workings. I'm not sure if you mean the mechanicals, or the electronics. But, they have to work together, and the stepper motor is the fundamental basis around which most of these machines are made.

The mechanical parts are simple...if it moves by turning a handle, it can move by turning a motor. It's just how you index the rotation of the motor that becomes an issue. The stepper motor is the solution.

A stepper motor is a special kind of motor that moves 1 "step" on command. The step is a precise portion of a full rotation, often 1.8 degrees. (200 steps per revolution) Your computer sends out a bit pattern through the parallel port, consisting of 1s and 0s...this instructs a "black box" driver circuit to make your motor move 1 step at a time, and in a certain direction.

Do you want to build your own driver circuitry, or do you want to buy it? Lots of good companies make them...one of the best is Gecko, run by a guy named Mariss Freimanis. He goes out of his way to help people.

Are you capable of building the mechanical parts of the machine? They're not that complicated...if you're mechanically inclined. One of the best resources on the net is run by the guy who inspired a lot of us...he has projects called "routezilla" and "morph." He shows LOTS of pictures, and sells plansets for his machines, as well as a well thought of driver circuit which uses a PC power supply for power. It's called the Piker. A quick search on google will turn up his name and his site URL.

If you give us a starting point for discussion, we can all be of help.

-- Chuck Knight

Thanks,

I'm looking at the plans from HobbyCNC. As far as I can tell, this is the easiest walkthrough set of plans from start to finish. I also found some information on the routezilla, pipe dream, and (something)7. Off of there I found some great links to more information. I can see my bank account is about to start dwindling!

I'm in north carolina today at a woodworking show and I see A LOT of small routers that look similar to these machines. There are a lot of people trying to break into this market, the minimum that i've seen a unit go for is 5k. I'd just like to build one of these units to make some parts for my RC helis.

Anyway, I need help on getting communication working between the PC and the controller. No one really gets into any depth as far as this goes. Is it because this is the simple part? I mean, everybody wants to talk about the actual building, no one wants to explain the communication. I'd at least like to see a simple diagram of the connections OR actual connections from the parallel port to driver cards.

This is what I want to for an experiment. Get a servo motor, and a small driver card. Then using my parallel port control the motor, no mechanics just control the speed and direction. Sounds easy? Please elaborate, I will graciously bow down to the stepper motor gurus!

Hey thanks for reading my long drawn out post.

Depending on your computer, download either Mach2 (winXP or 2K) http://www.artofcnc.ca or TurboCNC (DOS) http://www.dakeng.com
These are the 2 most commonly used machine control programs. Mach2 has an excellent manual available for download as well.

For a small router, probably the best bet for drivers would be either the Xylotex (both bipolar and unipolar) http://www.xylotex.com , or HobbyCNC's unipolar chopper. If you don't want to solder, the bipolar Xylotex is practically "plug and play". Be aware, though, that it is very intolerant of miswiring (as most drivers are).

Basically, you plug the Xylotex into the parallel port, connect a power supply and motors to it, start up Mach2 or TurboCNC, and start running. You can either run g-code files, or you can type in single line g-code commands.

Just noticed you said servo. Stick with steppers, much simpler to start with.

Those HobbyCNC plans are a looooooong way from a KOMO. :D

I've been to about 25 INDUSTRIAL woodworking shows over the last 4 years and I know a lot of the router guys pretty well since I ask so many questions. I know there's a big difference there, but because I know about those machines, I know where I want to go with this ... eventually.

Maybe I can contribute a little bit to this hobby's more advaneced features once I get into this. Ken Susnjara, which is the president of thermwood, has a great book about advanced features of CNC routers that may be helpful to a few of you who are wanting to expand upon your designs. His son gave me a copy a couple of years ago, but I think he sells the books for $25 a piece.

http://www.thermwood.com/twood_site/pages/books_and_multimedia/three_d_trim_and_machine.htm

He rambles a little bit about thermwood's history and other things, but there are several parts about screw harmonics, error checking, and other types of topics that might help out a bit.

Yep, I mean stepper. Just used to RC terminology.

Well, since you're a programmer, let me explain it in these terms.

G-Code is rather like postscript. It is an abstraction layer which allows a movement to be described in generic terms. During the setup of your controller program, you tell it how many steps there are in an inch...that sort of thing, and then the controller program does the calculations. G code simply says "move the X axis 1 inch clockwise" and the program translates that into the necessary number of output pulses for *your* machine.

Now, g-code is treated as an interpreted language...it exists as a simple ASCII text file, and is interpreted by a program we refer to as the controller. TurboCNC is a shareware controller program which is quite good.

TurboCNC (and all the other programs) will interpret each line, and output instructions by outputting a bit pattern through the parallel port directly. Consequently nearly all of them run under DOS or LINUX...direct parallel access under Windows is rather difficult.

Now, the hardware interface. Basically, it takes 2 pins to control a motor. One signals the driver circuit to make the motor take a step...the other changes state (0 or 1) to tell it which direction. Depending on your setup, the pins can signal a step by going high or going low...which is required depends on your driver circuit.

Unless you intend to build your own circuitry, which many people choose to do, you need only treat it as a "black box" interface that needs to be wired up. Pulse in one side, stepper drive signals out the other.

-- Chuck Knight

For the mean time, ill buy a driver 'black box' i'm going to take some baby steps getting into this.

As far as the output for the steps, the controller program (such as TurboCNC) pulses once per step? If so what is the maximum frequency of the step signal?

I prefer linux for programs like this so I'll also be investigating programs that run under that OS. Because linux programs are generally open source, there seem to be more features with those programs.

Thanks again

The step pulse frequency depends on cpu speed, but other factors can come into play. I think with TurboCNC you can probably get around ~25,000 steps per second. With Mach2 and ~1.5Ghz cpu running XP, you can get up to 45,000 steps per second.

If you want to use Linux, go to http://www.linuxcnc.org.