Hi all:

I am in the process of converting a Super X3 mill to CNC.  Still waiting on some pieces so I don't have anything to work with as of yet.

I've been reading the Mach3 docs, etc. but there is a very basic question that I am struggling to find an answer for.  One of the first projects I expect to attempt after getting things going is to mill a steel tube (perhaps 12 in long, outer diameter 1.5", wall thickness about 0.125").  I'll be milling various slots and holes through the wall of the tube.  At some point I expect to have an A axis with a rotary table so that I can rotate the tube but let's just assume I will mill the "top" of it  (what's directly below the cutter) for now just for simplicity.

I've drawn the tube in a CAD program and am putting the cuts/holes in the model.  My question is how does Mach3 or any other CNC program know what the shape is of the original material I am starting with.  My intent is to buy a steel tube of the right dimensions but how do I tell the CNC program it is starting out with a tube of specified dimensions?  I could just as easily put a solid block of metal there with squared edges and expect the cutter to whittle away all the excess material.  Obviously not a good idea but the point is how does the program know what it is starting with?  I must have to define this somewhere but I am clearly missing something.

Maybe a tube is too complex a case to use as an example with but even if I were going to cut a shape out of a rectangular block, don't I have to tell the program the starting dimensions of the block so it knows what has to be cut away?

Feel free to tell me I'm a dumb newb (I am!) but would be great to better understand how this works (or find out I am thinking about it the wrong way).

Thanks!!

XboxMeister

how does the program know what it is starting with?

Short answer.....It doesn't know.
You have to tell it where to cut. It does not know, or even care, if the cuts are in a pipe, a solid rod, a square piece of wax, or a human finger.
To put it in basic terms, what you normally do is determine a point on your tube to reference everything else to. Lets say the far left end of the pipe, bar, block, is X axis zero. the center of the part is Y axis zero, and the top of the part is Z axis zero. All of your features would be referenced from these points. You can input the proper G-code manually, or you can take your cad drawing, and import it into a cam program to make tool paths. Most cam programs have basic cad functions, and sometimes its just easier to do the cad portion in the cam program. Anyhow.....you, or a cam program has to tell the machine where to cut, because it has no idea without instructions. You might think of it like instructing a blind person how to navigate an obstacle course. They don't know what the obstacles are, or even care, there just going to step where you tell them to.

don't I have to tell the program the starting dimensions of the block so it knows what has to be cut away

nope. You have to tell the cam program the dimensions of the block so that IT can make a proper tool path to instruct Mach what to cut.

If all your wanting is simple slots and holes, the wizards that come with mach should suffice just fine. No need for an expensive cam program. You could even program them in manually without much effort. If you get that A axis, and start doing complex cuts, your most likely going to need some cam software.

P.S.   we are all dumb newbs at some point.

Mach3 does exactly what the g-code tells it to do. It has no idea what your cutting, or how to cut it. It just reads the g-code and sends the tool where the code tells it to. Sounds like you need a CAM package, which can calculate the toolpaths for you based on the material your using.

OK, thanks, that makes sense.  Sounds like I need to learn about toolpaths such that I can a) relate a starting point on the material to the cutting instructions in the g-code and b) define what parts of the model I'm building are to be cut away.  I'm creating the model of the cut object right now in BobCAD so I suspect that is where I am going to find the answersI am looking for in detail. 

I'm probably oversimplifying it a bit but let's say I have the basic uncut tube modeled correctly in BobCAD.  Imagine I cut a rectangular hole in the top surface (below the cutter) that is 0.5"x1.0".  Is the idea in BobCAD (or really any CAM) program that I in some way select the hole I've made in the tube CAD model and identify that as a cut the toolpath should make in the actual material?  Obviously g-code needs to get created beyond that, ...

Again, thanks for taking the time to answer my basic questions.

XboxMeister

I sure dont mean to sound discouraging but your journey has just begun! If you drew it in BC then have BC generate the toolpath. After drawing the part go to the data cam tree select stock and generate toolpaths.

You may want to take a look at the LazyCam Manual tutorials and just "scan" through them and see how a piece is drawn, the logic of knowing what and how you want to machine something, defining the cutting, etc. The material won't be of any value for using BobCad, but , most Cam programs all do the same thing.  Sounds like you need a basic understanding of how things are machined and there are books out there that can bring you up to speed.
RICH