I recently put together a C-Beam CNC from Openbuilds. It can mill through wood and metal and have a capacity of one square feet. I also have another machine which can mill 2*2 feet material. But when milling non-ferrous metal pieces they usually do not go beyond one square feet. This is mainly because of the cost of the pieces and the clamping required. Any material that crosses one square feet is usually CNC milled using an automatic CNC machine.
While the bigger machine has more power, I prefer using the smaller C-Beam machine because of its rigidity. Aluminium and Brass are relatively harder than wood so the frame of the CNC has to be strong. This is because when the router bit passes through the metal the vibration that is produced should not be translated into the axis too. If it does, then there will deviation in the milled parts which we do not want. So further down we will now see the three main factors that make CNC milling aluminium and brass a breeze.
All non-ferrous metals while CNC Milling require some kind of coolant. In some rare cases brass can be milled without coolant but that puts too much of load on the end mill. Using different types of end-mill can reduce the stress level on them but we will discuss that later.
So because coolant is normally used it is advised to use only metal clamps. The router rotates at 5000-6000 rpm and at these speeds the force exerted on the work piece is really heavy. The force is exerted from the top down (z direction) and also in the left and right (x,y direction). And thats why clamping it from the top and the sides are required.
The base plate is usually made of metal or polycarbonate. Both offers different strengths in their own way. Good things is both can be subjected to moisture. To clamp the workpiece from the sides, dowel pins are used. These look round in shape and are normally made of steel. Once slotted into the base plate they will never come out. And butting the piece to these dowel pins clamps them.
The router gives the rotational power in CNC Milling. But the actual material is cut using carbide coated End Mills. An end mill is held in router using collet. Most popular are the ER series collect and nut. If your router does not support a ER series collect then its time to upgrade. The collect comes in different sizes to accommodate different diameter of end mills. There is a chart added for your understanding.
The end mills are differentiated broadly into three types. Flat, Round Nose and V-Type. The flat end mill is used to clear away the material. The round nose end mill is using for smooth finishing passes and the V-Type end mill is used for engraving into non-ferrous metals.
Each of these bits comes with various flute counts. Flute is the cutting edge around the end mill which when touch the material at high speed shears of the material. The most common ones are single flute, double flute and 4 flute. For CNC Milling non-ferrous metals its is recommended to use single flute. These are a bit costly but they are the best for this purpose. Single flute is preferred over the others because when shearing of the metal, single flute tends to remove the metal quickly. Where as the others may have issues of clogging if the metal melts at intense heat. Thats where the feed rate comes into play which we will see next.
Aluminium melts at 660.3deg Celcius and brass melts at 900-940deg Celcius. While CNC Milling if the router is set 1000rpm and above then it is easy to reach the above mentioned temperatues. Then while milling instead of metal chips we can see clogging of metal on the end mill. This especially happens with Aluminium. Thus it is required that the feed rate is set very low at 200mm per second.
Feed Rate is the speed at which the router reaches from point A to B. The slower the speed the better the milling. But too much slowness will result in a longer period of milling which is a waste of energy. So it is important to find a balance.
Similarly the plunge depth is also measured in millimeters. This defines how deep the end mill goes into the metal at every pass. A typical wood CNC Milling can cut upto 4mm deep at every pass. But with non-ferrous milling we can remove only about 0.15mm maximum per pass. Any more than that then depending on the thickness of the end mill diameter we may break it.
So with the right information any dummy who is new to CNC milling can start working on aluminium and brass metals. Its in inevitable that you will make mistakes at the beginning, you might even break some bits but its all part of the learning. Every machine is not the same so you will understand your machine better only by trying. But starting with some knowledge about the different terms and what they do is necessary. And I hope that this article was able to give you that. If you have any question please contact me via instagram by clicking here.