NEWBIE!!! Confused with 3d Routering and Milling

[Sanghera]

Hi everyone,
I am sort of confused with all of this information about G-Code programming and all that. I have some 3d AutoCad drawings and if I have some 3d Rhino Drawings. How do I get those 3d drawings to convert to G-Code and then have that G-Code run my Steppers. I know of Ace Converter and that, but I am not sure if they are only for 2d Drawings, and if they can cut out a 3d part. Do I manually have to program the G-Code, because I do not know very much about G-Code programing. I was just wondering if anybody can help me.
Thanks.

[HuFlungDung]

Hi Sanghera,

How's the weather around Ask Me if Needed ?

That is a big question you asked. Basically, your 3d drawings are most likely not ready for direct cutting. This is because your surfaces and /or contours lie exactly on the outline of the object, thereby defining the object.

So starting from that point, you generally would have to "section" your part, to create slices of the model every so and so often. Then, each section is treated as if it were a 2d part, and an offset contour is made, to allow for the diameter/radius of the cutter you plan to use to cut the piece out.

Once you have created these offset contours, and perhaps joined them up, then you have the beginnings of a toolpath. So the toolpath really consists of a table of coordinates describing the distance from the present position, to the end of one of your screen entities that is contingent to it. When it gets there, then it looks for the next endpoint.

There are two ways for the machine to move to an endpoint: a linear straight-line move, or an arc movement. What will be missing from your table of coordinates, and which must be somehow added, is the G codes that will tell your cnc whether the move is linear (G1) or clockwise arc (G2) or counterclockwise arc (G3).

There is also the possibility that some movements will not be cutting movements, but simply Rapid movements to get the tool into position to begin the cut on a new chain of entities. This would be a G0 movement.

So you see, there is quite a bit for a gcode convertor to do, and to do it correctly for 3d work is very difficult to do in simple fashion. That is why we pay from hundreds to thousands of dollars for cadcam programs to help us with the task.

[ger21]

Download the MeshCAM beta from http://www.robgrz.com. It will create g-code from a 3d model. BUT, it must be in either .stl format, or a .dxf composed of 3D faces only.

[Sanghera]

Wow. HuFlungDung, so how would I "section" the part. Sounds kind of hard and complicated.
And Ger21 thank you for the reply, how does Meshcam perform? Does it make nice cuts?
Thank you all for your replies.

[HuFlungDung]

Sanghera,

I gave you that explanation, not intending that you actually go and do all that work That is just what is involved.

You'd best shop around and try out what the guys recommend. I use OneCNC software myself, because it does a good job of handling "real" surface models (does not convert to meshes). And, it is very simple to begin to use, without you having to worry about all the stuff that goes on in the background that I described earlier. You also get good simulations and toolpath previews to help check your machining processes before you start making chips. In fact, you might find machining is a lot more fun and a lot less work, and you can concentrate on creating your 3d models.

[Sanghera]

I have another question about 3d Models which is: If you make a model of, say a huge scaled pencil for example, how does the software and the machine cut the bottom side of the pencil? Without having a five axis machine. Do you have to cut one side, flip it and then cut that side? On a router? If so, how would you tell the machine exactly where the pencil is? I know these are kind of Newbie Questions.
Thanks.

[teilhardo]

You would have to use a 4th axis rotary indexer that cuts the top, rotates it 60 degrees around, cuts again, rotates...etc...

[ger21]

Do you have to cut one side, flip it and then cut that side? On a router? If so, how would you tell the machine exactly where the pencil is?

The final (or maybe next beta) of MeshCAM will include the ability to do multiple sides of your model. To do both sides, yes, you'll have to flip the part over. You'll have to make some type of jig to ference the part from so the two sides will line up.

As for how MeshCAM, I don't have a machine to test it on yet, but a lot of people like it so far, and when the final release version is available, it should be much cheaper than anything else available.

[ger21]

You might want to take a look at http://www.deskproto.com.

[Sanghera]

Thanks Gerry, and all.
When do you figure the Final Version will be out? Also, What kind of "jig" Do you mean? How would this jig work, could it just be a box that your piece would fit in, then you can just flip your piece and cut again? If the cut has a whole bunch of uneven surfaces, would just hanging it by the edges upside down work?
Thank you all for your replies.

[ger21]

When do you figure the Final Version will be out?

Probably the next 6 months or so. Just a guess, though.

What kind of "jig" Do you mean? How would this jig work, could it just be a box that your piece would fit in, then you can just flip your piece and cut again?

Yes.

If the cut has a whole bunch of uneven surfaces, would just hanging it by the edges upside down work?

Typically you leave some stock at the ends, or all the way around to support it when you flip it. Look at this example:

http://www.deskproto.com/gallery/cellphone.htm

[Sanghera]

Neat link. That's an interesting way, but will it work with a DIY router? And also, could you do it with some other software?
So, how would you or anybody suggest how to do this with other software on a DIY machine? Does this method only work with the Deskproto software and tools.
How can you program your software so that the cnc machine knows almost exactly where to start the cut, so that the parts align.
Thank you very much for your replies.
I really appreciate it.