Machine Capabilities

Alright, let’s assume you’re seriously considering building this, one of the questions I get quite a bit is how Capable is the machine. The real answer is it depends so in this section, lets talk about what it depends on.

Core Functionality

RIGCNC is a DIY VMC designed to cut metal (aluminum & steel) which inherently means it’s plenty strong to cut plastics, woods, composites, foam etc…

Rigidity

Rigidity comes from two things working together, stiff materials, and a geometry that allows loads to resolve in the shortest path possible. RIG uses, Granite, Steel, and aluminum as its primary building materials and the way the linear rails are constructed greatly improve over many other off the shelf linear stage models. The Added rigidity allows you to take heavier cuts. I regularly am able to 1.5 in^3 / min of aluminum removed. For reference that’s faster than most hobby mills out there, and more than 10x that of a pocket nc. The added rigidity also allows for a much better surface finish, that majority of surface finish issues come from chatter, which is much easier to manage on a solid machine. Also it goes a bit without saying but it’s easier to hit a tolerance when your mill is rigid enough to go where you tell it to, even when that means going through a material.

Work Area

The machine’s work area is purposefully limited. The focus of that design was on small metal components common in many hobbies. The design is configurable so it’s possible to massage a dimension or two in a specific direction if you have a need for it, but the rigidity of the machine is VERY closely tied with the mills stock profile.. In rough numbers, making an axis a little bit longer makes the machine a lot less rigid. For a cantilevered machine it’s roughly to the cube. Meaning if you take a 12 inch axis and make it 18 inches, it’s 3x less stiff, not the 50% that you would think was intuitive. This works in both directions though, if you can make an axis shorter, you can get a much more accurate machine using the same parts.

Spindle

The Spindle for the “vanilla” RIG version of the RIGCNC is a Sieg X2 Spindle head with an r8 Taper. Now that’s a lot of words, it boils down to; The Siegx2 is a reasonably precise Cast iron block that’s already the right shape and cheaper than just the raw materials if you wanted to make it yourself. R8 is the shape of the section that holds the tool, Typically Collets (of the r8 flavor) are used to squeeze down on the cutting tools, and provide enough holding power to mill effectively. Another benefit of this is the r8 system is the same system that Tormach uses for their TTS system. This unlocks the possibility of doing a completely automated ATC tool changer for a fraction of the price of a typical system. The downside to these castings is the bearings they use are incapable of going higher than about 8k rpm. you can buy higher grade bearings and replace them but that gets pricey VERY quickly.
The second most popular option is to use a VFD powered spindle. These come in several different flavors and KW ratings. These are fantastic for people who are only interested in machining non-ferrous materials (not steel)They have a much higher spindle speed, which is great for removing material in softer stock’s as well as smaller bits (more on relationship between spindle speed, tool diameter, and how the physics all plays nice together in the knowledge section) One common mistake that I do see often is picking a spindle that exceeds the max possible power coming out of the outlet. in the US, Mains power is 120 Volts RMS, most breakers are 15 amp, meaning the maximum amount of power available on a line is 1800 Watts, or 1.8 Kw. There are a ton of spindle kits on the market that are 2.2kw and up. When you have a machine that is capable of pulling more power from the circuit than the circuit can provide there’s a specific term in industry for this. It’s called a “Bad idea” Essentially you’re gambling that the cuts you’ve programmed aren’t going to push the machine hard, and if it does the circuit breaker is going to trip and cut the power. Bad news bears if you’re trying to get work done. The other possible options is your circuit breaker doesn’t work properly, the machine does pull the current it’s looking for and you start a fire inside your walls. Both are arguably bad. If you’re not in the US, you likely have 220 as your mains voltage and you can kind of do what ever you want. Even if you only have 10 amp breakers you’ve got 2.2Kw available.

Accuracy

This is a DIY machine, Much of the accuracy is going to be determined by how carefully its assembled, trammed and calibrated. That being said, it’s built from a combination of steel, aluminum, and granite, all of which have very different thermal expansion coefficients. additionally, a milling machines accuracy needs to be judged under load, and not just in a no-load condition. Achieving 0.005 in tolerance is relatively easy, 0.001 is possible with careful set up and acceptably accurate balls crews, anything below that is unlikely. The machines frame uses as much steel and granite as possible, but there is still relatively soft aluminum. It’s thick which helps keep it stiff, but aluminum is 2x less stiff than steel and there is no getting around that.

Summary

I was shooting to build a mill that punches above it’s weight class. I primarily work in metals and engineering plastics. Many of the mills on the market were focused on carving large sheets of material which leaves a ton of performance on the table, and many of the smaller machines used aluminum as their frame components, no doubt because it’s easier to work, but again leaves a lot to be desired when it comes to performance. I noticed a large percentage of people were sticking 800 watt spindles on machines that were only rigid enough to take a 20 watt cut and RIG is my first attempt at building a machine that was actually capable of pushing the power of some of the cheaply available spindles.