Knowing the Limits
When I was a young child, somewhere around the 5th or 6th grade, my dad traded some electronic equipment from his HAM hobby and brought home a mini bike. It did not work, but it was a beauty, at least in my eyes. Throughout the next few months, which seemed like an eternity, the mini bike became operable. Our neighbor who could weld designed, built and installed the belt guard. It was ready to go. However, I would have to take a safety course first. My dad was a smart man.
After a few days of riding, I was an expert and took off to the logging trails. It did not take me too long to find a steep firebreak. I headed towards the hill with the throttle fully opened. What happened next, I was not prepared for. You see, I thought that my mini bike had infinite power. The 3.5 HP Tecumseh powerhouse started to slow down until it sputtered and died. Unaware of the limitations, I thought it must have just had a momentary issue. After all, I started the engine and rode back down and it seemed fine. I would try again and again, but I had the same results. I reasoned that the belt was slipping, but if that were true then the engine would still be running. As a result of this childhood venture, I learned that my minibike had limits in power and speed. After a conversation with my dad, I learned that cars had the same issue and had minimized these with the transmission. That would explain why the trucks go so slow up the hills in the Rocky Mountains.
What does this have to do with CNC machines? The same principles apply. My first CNC mill was a desktop. I converted it to CNC myself and was happy with its performance. When cutting steel, I had to take it pretty easy or it would start chattering. You could actually see the head of the mill bouncing as the loads increased. I found and brought home a Bridgeport Series I CNC mill from Craigslist. This baby weighs over 3000 lbs and was the rigid ram model. There is no visible flex in the system. If you push it too hard the bits just snap like a spaghetti noodle.
With experience, I learned that cutting steel and aluminum require that I pay attention to the bit parameters and the “speeds and feeds.” These parameters would differ from the benchtop mill to the Bridgeport, and it takes some machine time to be successful. I am not a machinist in any form of the word, but I am starting to understand what I need to pay attention to.
The small CNC router is designed to cut wood and plastics. Wood and plastics are more forgiving when parameters are not set correctly. While other materials like aluminum can be cut, they require a bit more experience and have a smaller range of successful parameters.
If you are new to CNC and have a CNC router. I recommend you start with something simple. Make light cuts with slower feed rates. Then as you gain experience, you will know how hard you can push your CNC and still get good results without putting extra wear and tear on the machine.