Hi HSM Chief:
A lot of people will do virtually all burning with 3D or "spherical" orbit, which behaves exactly like the name states.
One detail however is that the path typically is a 2D simple orbit almost all the way down to depth and then expands as the burn energy drops for finishing while sitting above the bottom of the cavity by the orbit offset, then finishes the last bit by decreasing the orbit until there is no X-Y orbit at all right at the bottom of the burn.
Some machines may do it differently and move in all 3 axes at the same time, but the Hansvedt I'm most familiar with does it this way and I believe the older Charmilles machines do it that way too.
The principal consequence of this orbit path is that an electrode with sharp corners will burn a cavity with radii in those corners that is the same size as the orbit.
This can be a help or a hindrance.
When you want small radii in the corners of your cavity it's often easier to orbit them in than it is to mill them onto the electrode.
If you DON'T want them, you have to pick out the corners with vectoring toolpaths after the main burn is done.
Other big benefits of spherical orbits is that you always have space between the electrode and the developing cavity so flushing is better than with any other strategy.
You can make all your electrodes the same size and just increase the orbit to bring cavities to size and to final finish.
That means no dedicated roughers with different dimensions to plan and keep track of.
Spherical orbit also allows you to keep the electrode planning simple; a way I've used often is to take my cavity, and cut a plug from that cavity model (this is in my design software).
I then shell that plug with a shell that is the same thickness as my overburn.
I then cut another plug from the inside of that shell, and that's the geometry the trode needs...no planning, no thinking, just cut my shape and cook it into the job.
You can only do that simple protocol with spherical orbit...all other orbit strategies require more complex planning so the cavity ends up the shape you want.
Sometimes all this is not necessary; if you are burning a keyway or some other simple shape for example, you just make the electrode undersize and either do a 2D orbit or vector the trode toward each corner depending on whether radii are desirable in the corners or not.
So none of it is rocket science; a common truism is that 2D orbits are good for 2D shapes and 3D orbits are good for 3D shapes and for the most part that's not a bad rule.
If you can split up your cavity to get the 2D shapes or the ones that need sharp corners with separate trodes, and burn everything else with spherical orbit, you can cover most things that I've ever had to burn.
The other strategy that's super useful of course, is vectoring, which is not an orbiting strategy but basically points the electrode into the direction you want to go.
A simple Z axis burn is a vector toolpath that just happens to point in Z negative.
The classical place to use this toolpath in moldmaking is to use it to burn subgates without tilting the insert or mold base up on an angle.
Basically you point the tilted trode in the direction you want it to go, align it at the start point of the path and let 'er rip along the axis of the subgate trode.
It's fast and accurate and avoids a great deal of pissing around, so it's super popular for that task, but you can use it wherever you need sharp corners, by simply pointing the trode into the corner you want sharp and picking the corner out.
So a common way to make a sharp cornered square pocket for example, is to spherical orbit down to depth and then vector diagonally down in 3D into each corner in turn using the same trode you used for the main burn and just kissing the faces you've already burned.
That should help you to visualize how these various paths work and what they are particularly good for...your own ingenuity will tell you when and where to apply them.
Other orbits are left overs from another age; on many older machines for example, you can walk around the edges of a rectangular or other straight sided cavity almost as if you were milling it, but very few use these anymore as they have significant shortcomings and not much in the way of unique benefits.
With spherical and vectoring, there isn't much I cannot burn, and I suspect that most EDM guys do much the same.
Cheers
Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining
BTW just as an afterthought; you're probably going to get a lot more traction on this thread if you re-post it with a link to this one on the EDM sub-forum.
That's where the guys are who know this stuff in a lot more detail.
MC