Previously, I've talked about testing the Othermill--an out-of-the-box work horse--and the Shapeoko 2--a CNC kit ripe for re-invention. Today, I'm going to talk about a big boy, examining a CNC mill that's bigger, pricier, and commands a steeper learning curve. That's because we're adding another axis!
This is the MDX-540 with a rotary axis made by the Roland DGA Corporation. A 4-axis mill can do everything an X, Y, Z machine can do, but it can also rotate the cutting material around an 'A' axis. Essentially, this mill combines the functionality of a typical CNC and a lathe. With that additional axis, you're able to create complex double-sided objects and components with undercuts.
I'm fortunate enough to work at NYU's Interactive Telecommunications Program , where we have a bunch of incredible tools and machines. The MDX-540 is our latest addition to the shop and we're just beginning to experiment with it.
For all of my testing I mounted material in the rotary axis exclusively.
The Roland has an extensive list of material pre-sets to choose from, for my testing I stuck to primarily walnut, Delrin, and aluminum (my favorites). But what was new for me is how the material is secured to the mill.
When using the rotary axis, material is mounted in a way that is very similar to a lathe. One side is clamped down at the motorized end, the other is secured by a live center--a free spinning support. The material can be rotated while a spinning end mill cuts from above.
The other novel thing for me, you can use either flat or round (dowel) stock.
Double sided parts--any object that has a detailed top and bottom or an in and outside--can be milled from flat stock. All of the roughing and finishing is done to one surface, the stock is rotated 180 degrees, and then the other side is roughed and finished. Oh the possibilities, I forsee a lot of custom project enclosures in my future.
Tabs remain to secure the part to the remaining material and there is a faint seam line left after machining, but the surface finish is phenomenal. Post milling work will be necessary to remove any trace of the tabs, but no sanding needed for the rest of it.
Round stock mounts in a similar fashion, but the material is rotated for each pass and the part is milled all the way around. Want to make lightsabers, anyone?
Precision and Finish
As I mentioned, the surface finish of wooden pieces is incredible--it's incredibly precise to a point that there's no sanding needed for some materials. Delrin parts looked like they were cast or even injection molded. I didn't have as much luck with the finish on aluminum. There was a little chatter during milling and I don't think I was using the most ideal tool paths. I think with a little more CAM finagling I can get the results I want.
There is no other way to say it: the process of setting origin on this machine is nuts. The Roland comes with a calibration bar that you secure in the rotary axis and an electrode is plugged in. A calibration pin is chucked into the cutting spindle, and then the calibration cycle is run. At a very fast pace, the pin moves towards the bar (I think it's going to destroy itself everytime), right before a collision it slows to just barely make contact, and an electrical connection is made. The pin then moves to a number of other key locations along the bar, repeating the process. And all of this is just to set the origin of the Y axis!
This process is very well documented in the Roland manuals, it's just an involved process and nerve racking every time. Luckily, the mill "remembers" origin (even after powering down) and this makes running a job a little less terrifying.
This is the first mill I've covered that uses 3D models exclusively. Any CAD software that outputs to an .igs or .stl file can be used. I've had a lot of luck with Vectorworks.
The Roland comes with its own CAM software, the SRP Player, a wizard that takes you step by step through the process. Asking simple questions like material size and type, round vs flat stock, tabs/no tabs, bit selection, etc. This software makes what would typically be very difficult toolpaths easy to understand and execute.
Time to Mill
These jobs take a long time, hours, lots and lots of hours. We have a policy in our shop of never leaving a running CNC unattended. For one or two hour jobs, this isbearable, but I've seen some jobs estimated at 20-plus hours. Maybe I'll start reading Game of Thrones.
Noise and Mess
The noise the mill makes isn't bad at all, when cutting aluminum I didn't even need ear protection. Technically, the MDX-540 could sit on a desktop (overall dimensions 29.3" x 37.6" x 33.8"), but due to the uncontained mess, this is a shop only tool. I don't think anyone would be happy running this in an office.
So who's this for?
Someone with deep pockets to start. With a starting price of $20,000, I can't imagine the typical maker buying one of these for their home shop. This would most likely be in a school, a design company's prototyping shop, or a well-equipped makerspace.
That said, the Roland 4-axis CNC mill works incredibly well and is fairly easy to use. Now that I have the 4th axis, I'm creating parts I never dreamed I could produce. It's the kind of machine you definitely want to try at your local makerspace or tech shop.
Photos by Ben Light. Find more of Ben's projects on his website.