Enthusiasts and hobbyists with CNC routers might marvel at the durability and hardness of stainless steel and wonder if they are able to cut this desirable material. Perhaps you are accustomed to working with wood or other soft materials and want to create something a bit tougher.
CNC routers can cut stainless steel provided they have the correct cutting bits, however, you shouldn’t use a CNC machine to cut stainless steel since the material is physically very hard and for best results requires a constant flow of cutting fluid and a low bit speed to prevent work hardening.
Read on to learn more about cutting stainless steel with a CNC router, how you can do it and why it isn’t recommended. This article is by no means meant to discourage you – on the contrary, you may decide that you want to forge ahead and cut that steel by the end of it once you are better informed.
How To Cut Stainless Steel With a CNC Router
As explained above, it is entirely possible to cut stainless steel with a CNC router. To do this, you must have a good grasp of the metallurgical properties of stainless steel, as well as an understanding of your CNC router and its capabilities.
Stainless Steel Is a Hard Material
Hardness can be quantified and is metal hardness measured on the Mohs scale. The Mohs scale rates hardness on a scale of 1-10, with the hardest rating being 10 (diamond).
Stainless steel has a Mohs hardness of 5.5 – 6.3, and while this is softer than diamond, relatively speaking it is still significantly harder than the hardest wood. Wood doesn’t even register on the Mohs scale and its hardness is measured using the completely unrelated Janka scale.
What Hardness Means When Cutting Material
Hardness can be thought of as a measure of how difficult a material is to cut. Harder materials will require more work to cut than softer things like wood – this means you will need a high torque from your machinery, as well as an appropriate (harder) bit that is able to penetrate.
If you try to cut stainless steel with regular CNC bits you are unlikely to get very far – the harder material will wear out the bits, and possibly even the motors of your machine if you strain them too much.
To cut stainless steel with a CNC router you will need special solid carbide bits. These are made from a material somewhat harder than stainless steel. Be warned, having these special bits may not be enough – if you have never worked with stainless steel or any other metal, it must be said that it couldn’t be more different to wood. Unlike wood, metal changes at the molecular level in response to work.
Harder Bits for a Hard Material
You can get a set of carbide bits like these Router Bits made for hard metals (available on Amazon) and have at your stainless steel workpiece with your router, but there are some important things you need to know about working with them.
Hardened CNC bits tend to be much more brittle than normal, and are likely to snap if they get too hot or “bite” into the metal.
We will discuss cutting fluid in more depth later on, but one of its purposes is to prevent the cutting bit from biting into the metal and snapping. The main takeaway here is that hardened bits are fragile in their own way, even if this seems counterintuitive.
Stainless steel, like many other metals, goes through a process called work hardening when exposed to high forces – such as a blacksmith hammering it into shape – and for this reason, you cannot work too quickly with it.
The heat generated from cutting into stainless steel affects its molecular structure causing it to harden in response. The faster you try to cut it, the hotter it gets – which is why a low bit speed of 800-1000 RPM is recommended. Slower is better, as a general rule, however, a lower speed can put more strain on your CNC router.
The work hardening process is useful because it allows for the creation of hardened tools that last much longer. That said, if you are trying to shape or otherwise alter the metal, this will work against you.
We referred to cutting fluid at the beginning of the article. For the uninitiated, this is a liquid that is applied to the work area when cutting or drilling metal to help cool the metal and offset work hardening. It also cools the cutting bit and helps to keep it from biting into the metal.
If you are planning to cut stainless steel with your CNC router you will need to apply cutting fluid throughout its operation. This makes the process somewhat more laborious but will give you a smoother cut and help your cutting tips last longer.
You can get Forney Tap Magic Pro Cutting Fluid (available on Amazon) which is suitable for ferrous and non-ferrous metals, but the small 4 oz. (118 ml) bottle may only be enough for a handful of small pieces. It may be enough for you to experiment with – rather do a couple of small pieces to get the feel of working with the material before you take on anything ambitious.
CNC Milling Machines
If, at this point, you are scratching your head and wondering how some people get those perfect cuts of stainless steel if they are not using a CNC router, look no further than CNC milling machines.
CNC milling machines are similar to CNC routers but are designed for harder materials like stainless steel. Rather than the rotary bit moving around the workpiece to produce the cut, the workpiece is moved through a high-powered cutting apparatus.
Essentially, purpose-made metal CNC equipment moves the workpiece rather than the cutting equipment. Having a fixed rotary bit allows CNC milling machines to incorporate much more powerful motors. Naturally, this makes them significantly more expensive than their wood- and softer material-oriented cousins.
Manage Your Expectations
If you do decide to take on a stainless steel workpiece with your CNC router, the best advice we can offer is that you should manage your expectations.
Cutting stainless steel with a CNC router takes a long time – you need to operate at a low speed to prevent work hardening and straining your equipment, and by its nature, a CNC router will not cut as well as a purpose-built milling machine.
You will have to decide if it is worth your time, effort, and energy trying to cut stainless steel with a CNC router. It may be prudent to opt for a softer material instead, especially since the quality of the cut might leave you wanting.
While it is entirely possible to cut stainless steel with a CNC router, generally speaking, you are not going to get a perfect cut due to the hardness of the metal and the inherent weaknesses of a CNC router when compared to CNC milling machines.
That said, with the right equipment and enough patience you may be able to realize your dream project in stainless steel. If nothing else, try out 1 or 2 small pieces before tackling anything ambitious.