Newbie questions

[NeoMiller]

Can someone please answer some newbie questions

Assume that I have made a 3D drawing in a CAD program (Rhino) of a simple piece of wood with 2 rectangular cavities 1inch deep side by side and I want to mill out the 2 cavities using a desktop CNC mill. I want to use 3 passes of a coarse cutting tool (each pass milling out about 1/3inch leaving about 1/16th inch on the sides and bottom and then a final finishing cut to remove the last 1/16th on all sides with a fine tool.

1. The size of the piece of wood in which the cavities have to be milled out is not important. Nor do I need to cut the outer boundries of the piece by the CNC mill. I am confused how do I draw the outer boudry of the wooden block and how do I prevent this information to be given to the CNC machine.

2. How do I convert the CAD drawing to the toolpath described above with all the offsets, passes and 2 different tools. Is there a software to do that or does Rhino does this Job. Does BobCAD do this work.

3. I converted the Rhino file to DXF file and had a look at the DXF file in BobCAD. It shows a lot of lines as compared to the drawing in Rhino. Are all these lines the tool paths. I am confused about how DXF stores the 3D object information.

4. Is there some webpage, PDF, or FAQ avaialable giving some basic information on how all this is done in real practice.

Thanks for any answers.

[HuFlungDung]

Hi Neomiller,

Since you have access to Bobcad, why don't you work your way through the tutorials and read the help.

Bobcad does not create the toolpaths automatically upon importation of the file. You will have to do a bit more work than that

Typically, when you draw something in a straight CAD program, you draw the part itself. You might be drawing this in 2d or 3d. To use a program like Bobcad, you will end up drawing what we call an "offset toolpath". This will be likened to a series of contour lines that follow the outline of your part, at a fixed distance from your part contours. This distance will equal your cutter radius, plus any finish allowance.

Bobcad (up to version 18) has some functions that will simplify the drawing of some of these paths in special situations. These would include pocketing routines, which will create a toolpath to clean out or finish mill a straightwall pocket, with or without islands. Drawing a "skin" is also another method of creating a toolpath wireframe next to a 3d object (one where simultaneous moves in all 3 axis may be required.)

You mention how to differentiate between your rough blank and the finish profile. In Bobcad, you can use your imagination a bit and create a "pocket" on the outside of a part, and then create quick toolpaths to rough all the excess material away. However, if you choose to mill only the profile, then you can ignore (at some peril!) the outside dimensions of your rough blank, and just mill the final contour offsets. I say at some peril, because you may need to watch that all your Z plunges are carried out in a safe area, at a safe feedrate, because of the existence of material in the area outside your profile zone.

I don't know what your Rhino part looks like to give you a comparative answer of what the "extra lines" are about. Probably if you post a file (in dxf format), someone will render an explanation of what you are looking at for machining purposes.

[peter]

hi neomiller
hu as answered your question
my imput is the extra lines
because you have drawn in 3d and exported it bobcad as also
imported the extra lines where the surface bounderys are in the
3d model
best regards
peter

[ger21]

When you convert a 3D object to .dxf, the surfaces of the object usually get converted into many smaller surfaces, called a mesh. Meshes can be either small squares, or triangles, or you might have both. These are the lines you're seeing. I'm not familiar with BobCad, so I can't help you there. Generally, some type of CAM software will generate your toolpaths and G-Code from your model. Most are quite expensive. The cheaper ones tend to mill the entire object, not just the pocket. If you want to just machine the pocket, drawing in 2D is probably the best way to go, and then use ACE converter (free).

Gerry

[cadcam]

ger21, DXF bascilly does not support surfaces and solids. By your statment you are defineing a Conversion of a STL file conversion.

[ger21]

By surfaces I meant meshes and faces, which .dxf does contain. I was just trying to explain what he was getting when exporting a .dxf from Rhino. I didn't say anything about solids, but AutoCAD 2000 .dxf's can contain solids, but I don't think anything else would read them. Sorry for the confusion.

Gerry

[imserv]

Hi Neomiller,

Here are a couple of links that may help you get to where you are headed.

If you use Rhino, you can export an .stl file and machine it with StlWork:

http://www.stlwork.com

or DeskCNC

http://www.imsrv.com/deskcnc

You can also use a program like Vector Cam which can directly import your Rhino nurbs surfaces as IGES files.

A couple of examples of the kinds of toolpaths that are available in Vector are in these tutorials:

Heart: http://www.imsrv.com/discus/messages...tml?1025809852

Starfish: http://www.imsrv.com/discus/messages...tml?1027172853

and here: http://www.imsrv.com/discus/messages...tml?1042958252

[turmite]

Fred thank you for the excellent info. I also have Rhino and have been looking for an inexpensive way to carve my products. I will down load the demo later and give it a try.
turmite