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G-Code, CAD, and CAM discussions / Re: Probably a REALLY basic question....

« on: October 08, 2008, 09:07:11 AM »

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

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G-Code, CAD, and CAM discussions / Probably a REALLY basic question....

« on: October 07, 2008, 10:28:11 PM »

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