Let's Make Robots!

CTC CNC Step 2 (Ordered Parts)

Yup, I'm gunna do it. I am building a CNC.

Oh, where do I start? --Seriously, where do I start?

Ok, so of course, I have found a lot of Chinese stuff, mainly this board. Of course, too good to be true --4 motors, drivers, controller all for 220 bucks. A few forums later and of course, I read stories of blue smoke when just testing the board with a meter and a hard time trying to get a replacement from the manufacturer. Then again, that price is wicked tempting and it looks like it will talk nice to mach3. I suppose I would need a USB/parallel cable as well.

If I skip that option, I am in the vast Ebay sea of drivers, individual steppers, packages of steppers, etc. Not to mention, I can also design and solder my own driver boards of course. --Going to be a lot of learning/shopping/forum reading on this one.

The hardware does not look like much of a problem, I of course, can weld and have all of the metal fabrication stuff I need so I am covered there. In terms of glides etc, I am looking at $500-$600 sets (Ebay) including: supported linear bearings (not just the rails but the heavier ones with the full-length T-shaped support below it), the ballscrews and ends and the couplers. $600 gets you a set that will allow a machine around 3' by 3' by 1' on the Z axis. Not too shabby in terms of size. I already have designs and ideas in my head for the frame, etc --this one should not be hard (in terms of my skills) and I am not worried about this at all. --For the record, I am thinking I want to do a sliding table for the Y axis, and a fixed gantry with the X and Z attached.

Now comes the hard part....

Assuming I will not go with one of those "all in one" boards, and assuming I can figure out the drivers, this leaves me with the controller board. My goal here is to build a CNC that can not only mill (I will be using a Porter Cable 690 router) but I also want it to print as well (i.e. reprap). Now, most CNC's sorta have "CNC Brains" in them and RepRaps have an Arduino in them. And that's about as far as I have gotten. I am simply not going to go to all this trouble to build this machine unless it can do both. Period. The question is (and what I am pouring through forums to find) is, can a reprap mill or can a CNC print? 

At this point, I open the floor to any and all folks that have done anything similar to this. Like I said, I am at the "forum reading" stage and have a TON to learn. I will take anything you guys have.

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I have to agree with TinHead. Yes, you will spend about $1200 for the pair of machines, if not more. But, you won't have any switching and swapping to do. If you were to follow the dual purpose road, you should consider designing a board like TinHead did and get it to talk to the stepper drivers that you use for the CNC. You will have to have the extra wires ( 4 for the bipolar stepper, 6 or 8 for a unipolar, 2 for the hot end and 2 for the thermistor ) routed for the extruder, hot end, and thermistor. You wouldn't want to have to add them every time you decided to print.

To answer your question, yes a CNC can print. As TinHead pointed out EMC2, free, configurable machine control, will run a reprap. There is more configuration than a blip here and a blop there.

I completely disagree with Dan. Using a PC-type processor will not make the machine run any faster as you weakest link is the stepper motors. A PC-type processor will just sit around twiddling it's thumbs faster while it waits for the steppers.

Driguana2000 has done a great tutorial on driving stepper motors and has even supplied the design for stepper motor driver PCB's that allow you to overcome many of the stepper motors speed issues.

The PCB design and software is freely available here:


That is why I said, "-at least if there are chips that latch the commands going to each axis".  --so the processor can do other things (calculations, etc.) while waiting.

ADDED:  For example, if you are cutting (or 'printing') a curve, it will take a lot of mathematical processing at each step of the curve. A PC-type processor can do these calculations rather quickly, while a micro-controller will be slow at it, and is pushing its abilities to even do such computations at all.



It really does have a lot of good stuff in it. Alas, it is nowhere near as big as I need. I am currently looking at a machine with 1030mm leadscrews on both the x and y (yes, a 3'x3' machine) and thus, are looking more toward NEMA34's at around 900 oz/in. The info I have on them puts them at around 7.8A. Besides, I have done a lot more Ebay'ing and (skipping that silly all-in-one board) I can get all the motors, with controllers and a power supply cheaper than I can buy parts to build drivers.

Still confused about this whole software thing though. I see the boards with a huge parallel connector for 25 bucks, I see reprap with a nice simple Arduino and ready-to-go code. Then I see folks are designing here, then running the design through this or that, then sending it to mach3 or some other thing.

Overwhelmed... I wish I could just focus on welding.

<g> Funny you should say that... My other brother (the master machinist) is building a "CNC"-type welder.  (Still in the startup stage on that project so far.) He is planning a heavy-duty unit, but then he plays with some pretty big machines.



You asked, "can a reprap mill or can a CNC print?"

My answer, "Yes" (-with explanation to follow)

[I have not personally built a CNC, but one of my brothers is working on one.] --Anyway, since the major function of the "brain", no matter which kind you decide to use, is to position the head in the X, Y and Z directions, that part is the same whatever type head it is positioning. If you are "printing" you also need to be able to turn the extrusion on or off, while on a mill, they usually just let it run, but the brain will need a fourth "axis" or control channel for extruder/cutter on/off.

The other thing about using a μ-controller (Arduino, Picaxe, etc.) is that the CNC may run more slowly since the speed is limited. Using a PC-type processor will allow higher speeds, -at least if there are chips that latch the commands going to each axis, and the processor can control more than one at a time.

ADDED: PC processors run on the order of 1000 times faster, which facilitates computing complex movements of motors for each axis on-the-fly. These can be computed while waiting as the step-motors are moving into the positions dictated by the last set of computations so the cutting or 'printing' will not have to wait while motor movements for a complex curve are calculated.

I am in a unique position to actually do this up. I am lucky enough to have the tools (especially steel work), time and a (small) bit of dough for this project and I hope (intend) to do it right the first time. I am actually considering being able to run this machine wet. That is, with constant-flow cooling. To cut to the point, if I could get through aluminum plate, I would be stoked. 

I know I am asking the world, a CNC that will do wood, light metal and 3D print, but man --how hard could it be?

Dual brain.

As you figured your self, the mechanics is mostly the same. So are the driver electronics. Left is the software. But it would be easy simply to have two controllers laying around if you do not feel you are into merging the two pieces together, and do not want to upload code to the controller every time you switch tool on the machine.

If I were to build such a thing, I think I would opt for having most of the brain in a PC where it's easy to load different configurations or programs depending on the tool mounted and the task given.

An other question, what material are you going to mill in? Not extra hardened steel I guess, or?

I am wicked curious as to how the software path works... I would like to know what folks are using to design, and then how that design gets to the USB cable. I see "mach3", "Gcode" and a bunch of other stuff go by --I am a bit overwhelmed with this one. --A solid frame, I got that one --1's and 0's? Not so much...