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Topics - rrmerlin60

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General Mach Discussion / Questions about Creating Tool Paths
« on: November 08, 2012, 09:56:36 AM »
I hope I word this in an intelligent way, but I have been curious about how any program like Mach3 takes any large piece of aluminum and whittles it down to the right shape. And more specifically, how it knows where to begin the cuts.

Let's say you start with a small block of aluminum on a mill table, and the goal is for a 1/2" ball nose end mill to create a semi-sphere. You're using a 3 axis mill.

How does the program know what the initial conditions are? I mean, how does it know that you have a square block of aluminum, and not to start by traversing right to the surface of the semi-sphere? Is there some place in Mach3 that you input the original size of the block that you start with?

Is there also a place where you specifiy the maximum depth of cut that you allow (say .025") and a finishing cut depth (.003")?

I know that I create a 3D model in software, then have that translated to G code, but I don't undertsand how the machine knows that there's a whole block of metal in its way.

This is a very basic question, but any help on this? Thanks, Tom.

Hello Group;

I am completely new to the CNC world, and have got to the point where I have working stepper motors on a bench. I use Mach3, and the usual hardware. Ultimately I want to create a 3D model in Rhino software, then carve it out of metal or wood on a vertical mill (maybe a gantry router). Typical stuff.

I simply need a bit of clarification on the steps in between. I assume  (but please correct if I'm wrong) that I model a 3D shape in Rhino, my favourite software, then save as a DXF file, then convert that file into a G-code file that Mach3 can load and run. Assuming that this is a fairly basic and machinable shape, is my Rhino-to-mill table path correct?

Also, I know that there exists a RhinoCam software that presumably takes 3D models and does all the conversion to a ready-to-machine file, but at $1200 this is too steep for my early purposes.

Is there any free or demo software that can do this? Or, have I made bad assumptions in how I'd approach this?

In the beginning I start with a 3D Rhino model, and in the end, I wish to have the wood or metal shape after it's been machined. Basic questions, I know, but that's where I am for the moment.

Thanks to all who may assist. Tom.

Hi Everyone.

I'm new to this forum, but pleased to annouce that I now have stepper motor movement, at least on the bench. Mach3 seems to be working exactly as hoped. I had a devil of a time getting the old Camtronics driver boards to communicate with my new C10 Breakout board. But all is working now, and I have a question about tuning and stepper "jitters."

When I installed the evaluation version of Mach3, and studied the tutorial videos, I then went to load some Gcode samples that come with the Mach3 files. These seem like a good starting point. One code is called something like "Ball" and it causes the x axis motor to run at full speed, then very slowly deccelerate until stopped, then very slowly accelerate until full speed.

When the motor hits a certain low speed, both deccelerating and accelerating, it "jitters" like it can't handle this speed. No matter what I do in the Motor Tuning window, it always does this jittery movement.

So, is this the whole point of this sample of Gcode? To help us locate the problematic area of the system? Is there a way to correct this? My drivers do not do X 10 microstepping, like the Gecko's can. And there's no mid-band resonance circuitry to compensate for this rough motion.

The good news is, that I've set my acceleration and velocity to values that seem to operate smoothly in jogging and fast-jogging. I can't be sure if my motors will ever encounter a speed that will cause them to jitter while machining something. It seems logical that they will encounter this speed, since it's greater than zero, and less than full rpm.

Any thoughts on how to deal with this using the tuning in Mach3, or other methods?

Thanks, Tom.

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