Hi, I actually bought ViaCAD for this specific purpose (also useful as a general CAD system). My plan was to be able to draw 2.5D geometry, and use those lines directly for 2.5D milling (through SheetCAM - there's a post here somewhere a few years ago), and also to simulate the finished part shape with surfaces or solids after cutting. For example a bullnose cutter used to cut a flat section with a boss, then profile the part to cut it out. That way I could both design complicated 2.5D products (with tool ramps and bullnose cutters etc, so it's really very complex 3D) and view the result in the same design file without having to resort to a CAM simulator. This is all a the "DIY" level of cost.

I had tested the "lathe" tool, and that worked well.

When I went to do it in real life, I tried using a sweep of the tool profile, and saw the error(s) of my ways:

• you can only sweep a 2D profile, so no "caps" (without extra half lathed tool at path ends)
  
• tool doesn't remain vertical on ramps
  
• tool can't "self intersect" ie centre can't move on radius less than its radius, eg square corner
  

And possibly other geometrical problems. I've just found a thread on here that suggests this is well beyond ViaCAD's 'pay grade' so I might have been on the wrong track...

http://forum.punchcad.com/showthread.php?t=3726

But I would be keen to know if there is a tool or technique which will do this with relative ease and not too much inaccuracy. The toolpaths I'm cutting would probably be limited to 3D lines and helixes about the Z axis, ie simple G code commands.

- Antony.

Thanks for the ideas. I don't really know what a "face" is (not a big 3D CAD user!), I tried sweeping a surface, but it will only sweep a closed line (I have v8 BTW, Viacad basic-est 3D). I guess a section would be better. I think I did manage to make a cap once, by revolving a profile of the tool, but rather non-automated away around it (compared to the (im)possibility of sweeping a solid that is the cutting tool over the toolpath).

I hadn't thought of doing each piece of the toolpath separately then adding them. This may be practical because most of the things I want to visualise are composed of only a few arcs and lines. I'm not so much after a full 3D simulation of the cutting process, but to be able to place the cutter during design to avoid too much trial and error. I have actually been drawing in 2D CAD I am familiar with, using SheetCAM to CAM that, then adding things like helical ramps manually to the Gcode.

I did notice that the sweep options have a "rigid" option, this comes closer to what I want, in that it will hold the swept profile rigid in rotation, ie it will keep the tool vertical like it would be in the machine. Main problem with that is it can't orient itself to follow the curve of an arc in the xy plane for example.

There's also an option to allow self-intersection which I haven't tried yet.

It ultimately needs to be a 3D solid or surface that is being swept, because different parts of the cutter touch the material being cut depending on which way it is being moved. Sounds like an extremely complex way to define solids, I don't know if even high end CAM systems can do it with any precision. Milling simulators generally step the tool and subtract thousands of bites from the material to be cut.