Intro to 5 Axis Machining
Five axis machining is both intriguing and confusing for many users. Since we plan to start offering our 5 axis machine by late December 2018 or early January 2019, it seems like a great time to address some of the common questions and points of confusion.
It is easy to picture 3 axis movement in your head. X moves left to right, Y moves front to back, and Z moves up and down. So how do you get more axes (yes, “axes” is the plural of “axis”) than that? Rotationally. X, Y, and Z are linear axes, while A, B, and C are rotational axes. The A rotates around the X, the B rotates around the Y, and the C rotates around the Z. To better understand this, make a “thumbs up” sign with your right hand, then point your thumb in the direction of positive travel of the X axis. Think of your thumb as the X and your four fingers curled up as the A. The direction your four fingers are pointing also represent the positive rotation direction. This “rule of thumb” applies to Y/B and Z/C as well.
Five axis mills and routers are typically going to be XYZAC or XYZBC. The one we’ll be offering is an XYZAC. There are a couple different ways you can achieve these rotations. Some machines will rotate the spindle, often forming the B axis and also rotate a platter on the table to form the C axis. Ours will mount a rotating platter (the C axis) onto a trunnion table mounted along the X direction, forming the A axis. This configuration allows you to mount the rotational axis to the table when you need 5 axis capability, but remove the rotational mechanisms when you just need to do 3 axis work.
Indexed versus Simultaneous
There are two ways to use a five axis machine. On the more basic level, they are just used for indexing. This means that you move the rotational axes (A and C for our purposes) to some angle combination to present a particular face of the stock to the cutter so it can then do three axis work on that face. Think of a cube being rotated to present the next face until all the machining is done.
Simultaneous 5 axis work is what’s really impressive to watch (See a video of a high end industrial XYZAC doing simultaneous 5 axis work here). This involves the machine moving one or more of the rotational axes while it moves one or more of the linear axes to achieve a complex geometry that would not otherwise be feasible with a 3 axis machine, such as an impeller.
Pros and Cons of 5 Axis
Let’s start with the downsides of 5 axis. First, because you are adding additional mechanisms to the mix you are of course adding additional sources of slop, backlash etc. Every mechanical mechanism has some amount of imperfection, so the more you add the more those imperfections stack upon each other. On our machine, this isn’t significant, but in theory its true. Next, the work size capabilities of a 5 axis machine can be limited by clearance matters. The part must be able to rotate on the platter without colliding with the trunnion or the spindle. Finally, five axis work is inherently more complicated than a three axis work. The CAM work is somewhat more involved and you need to do a bit of planning to avoid collisions.
So why do you want a 5 Axis CNC machine? First, certain shapes just aren’t reasonably machinable on a three axis machine. Other parts could be done on a 3 axis machine by manually indexing the part, but would be done much faster with a fraction of the setup time on a 5 axis machine. Imagine a cube shaped piece of stock. Being a cube, it has six sides. Let’s further assume that you need to put features on all 6 sides of this cube and that you need to chamfer all the edges. With a 3 axis machine, you’d need to machine the first face with your flat end mill then change to your chamfering tool and chamfer the edges. You’d then need to unclamp the material, turn it to present the next unmachined face to the Z axis, realign everything exactly (this requires you to be very careful), then reclamp it. You’d have to do this 6 times to machine all the faces.).
With a 5 axis machine, you could machine 5 of the 6 sides and chamfer 8 of the 12 edges with one setup using the same flat end mill since the machine can move in ways to present everything except the bottom face of the cube to the cutter. So, in this example, with a 3 axis machine you’d have 6 setups and have to do a total of 7 tool changes to finish the part. With a 5 axis machine, you could do this with 2 setups and no tool changes! You’d put the cube on the platter, machine 5 of the sides and be able to rotate the machine (via your g code program of course) to chamfer 8 of the 12 edges with the flat end mill. From there you’d flip the part over and machine the remaining side and the chamfer the remaining four edges. Huge time saver! Put simply, a five axis CNC machine can run circles around a three axis machine on certain types of work.
5 Axis Programming and Control
Fusion 360 allows you to do 5 axis CAM in the hobby license version and in Fusion Ultimate. There are a lot of great videos on Fusion 5 axis CAM such as this one and this one that are worth taking a look at if you think you have what it takes to 5 axis machining.
There are also some post processor modifications that need to be made to tailor the CAM output to the machine’s characteristics. Parameters such as the preferred rotation direction and maximum rotation angles get defined there. We have worked out these details and will provide it with the machine.
We are most likely going to provide a computer preloaded with LinuxCNC and a pre-built 5 axis profile tailored to the machine. LinuxCNC is a break from our tradition control choice, but LinuxCNC is a proven solution capable of efficiently controlling simultaneous 5 axis motion.
We are working out the final details on the 5 axis machine before we launch it, but please stay tuned. We’ll have videos and further information about the machine soon. Get in touch with us at email@example.com if you are interested in more details.