Feeds and speeds

Why is choosing the correct feeds and speeds important in CNC milling? A user must be able to balance several factors to ensure that he or she gets the best results. Picking the right feeds and speeds for your Mill One is a critical step in making sure your cuts are accurate and look great. Feeds and speeds can vary a lot depending on the material you are cutting, such as the type of end mill you use, the speed of the router, and the rigidity of the machine you are using.

Here we will discuss some terminology that will help beginner users understand this topic and provide some recommendations in what feeds and speeds to start off with.

This guide is designed to give you a basic understanding of different settings to use with your Mill One. Sometimes it will take some trial and error to dial in the right settings for your setup and materials to get a balance of speed, finish quality, and precision.

Feed rate

Feed rate describes the speed of which the end mill moves. In most CAM software, the user will choose a “feed rate” which refers to the speed that the end mill moves in the X and Y direction. For example, setting the feed rate to 500mm/min allows the machine to move the end mill through the material up to 500mm in a minute.

Plunge rate

The plunge rate is very similar to the feed rate, however it describes the maximum speed that the end mill can move in the Z direction.

Depth of cut

Most CNC machines will take multiple passes to cut away at a material rather than taking all the material away at once. The depth of cut describes how deep the end mill will cut through at every pass.

Spindle speed

Spindle speed refers to the speed at which the end mill rotates in the rotary tool you are using. Most compact routers operate at speeds between 10,000 to 30,000 RPM (rotations per minute). Check here to see our recommendations.

Deflection

Deflection in this case refers how much the end mill of the CNC machine gets displaced from where it should be. The larger the forces which act upon an end mill and other parts of the machine, the larger the deflection is. Deflection plays a large role in how precise your CNC machine is, and steps must be taken to reduce deflection to an acceptable amount. Stresses on the CNC machine can be reduced by adjusting settings like the feed rate and depth of cut to reduce the deflection to an acceptable amount.

Hardness

The technical definition of hardness is the ability for a material to resist deflection. A rock is harder than an rubber eraser because you can bend a rubber eraser far more than you can a rock with the same amount of force. This concept plays an important role in CNC milling because the harder the material is, typically the more difficult it become to mill. Because the forces that are exerted during cutting is higher on a hard material than a soft material, we must set different parameters for each material to get the most optimal feeds and speeds.

Recommendations

In this section, we will talk about some recommended feeds and speeds for your Mill One. These feeds and speeds are meant to be a starting point in finding the right parameters that work best for your setup. Feeds and speeds listed on this page have been tested to work with 1/8″ and 1/4″ two flute carbide end mills. Learn more about choosing end mills here.

Unless you are doing 3D contour cutting where the Z axis moves up and down a lot, it is recommended that the plunge rate be set to a fairly slow rate. A plunge rate of 100mm/min to 300mm/min is appropriate in most applications.

Foam

Foam is a soft material and thus an extremely forgiving material to carve. You can typically set aggressive feed rates and depth of cuts for this material, up to 1200mm/min at 4mm depth of cut. Pick the lowest speed on your router when working with foam since the foam may melt onto the end mill if the speed is too fast.

Wood

The hardness of wood varies by species and other factors. However, most commonly available woods such as pine, oak, cedar, maple, or cherry are quite easy to work with. A depth of cut of 2-3mm at around 700mm/min works well with soft to medium hardness woods, but you can reduce the depth of cut to around 1mm if you’re working with a very hard wood. Medium speed on the router at around 20,000RPM works well.

Acrylic/Polycarbonate/HDPE/PVC

These plastics are lovely to work with and the Mill One can handle milling these materials at medium to high feed rates of around 600mm/min to 1000mm/min. However, these plastics have a tendency to leave burrs and debris around the cut that need to be picked off if the right speeds and feeds are not selected. Choose a low spindle speed near the bottom of your router’s speed range and a depth of cut of around 1-2mm, and adjust these settings to get the best results.

Aluminum

Aluminum comes in a variety of alloys, but the most common is 6061 Aluminum. It is a fairy hard and strong material and can be found in aerospace components and bikes. The trickiest part of milling aluminum is preventing the aluminum chips from melting and binding to the end mill, which will stop the end mill from making cuts. This means setting the right feeds and speeds so that the milled aluminum chips are at the appropriate size to carry heat away from the end mill.

Shallow cuts of 0.1mm to 0.2mm for the depth of cut at 1000mm/min is a good starting point for milling with smaller end mills (1/8″ and smaller). If you have larger end mills use a slower feed rate of around 500mm/min, start off with shallow cuts of 0.1mm to 0.2mm, and bump up the depth of cut to 0.3mm to 0.5mm if your setup can handle it.

Choosing the right spindle speed for milling aluminum has been a highly debated topic for hobby CNCers. In traditional machining machines, the spindle speeds are set low, typically at around a few thousand RPM. Routers like the ones used on the Mill One however, run between 10,000RPM to 30,000RPM. To get around this, the technique typically employed is to use lower number of flutes (one or two), slower spindle speeds, shallower cuts, and faster feed rates.

Brass

Brass is typically harder that aluminum, but can be easier to work with since brass chips will not fuse to your end mill as readily as aluminum does. With a sharp end mill, the Mill One can cut brass at 0.3mm to 0.5mm depth of cut at a feed rate of around 150mm/min. A moderate spindle speed of 18,000RPM to 20,000RPM will suffice.

Steel

It is not recommended to use the Mill One to cut steel. Due to the hardness of steel, milling steel can take a very long time and will cause your end mills to dull rather quickly because the Mill One is not designed to cut steel efficiently. If you do insist on using the Mill One to cut steel, try a depth of cut of around 0.2mm at 50mm/min and a spindle speed of around 20,000RPM.

Printed circuit boards

PCB milling can involve engraving, drilling, and cutting, all of which are different processes that may require different settings. Here are some basic guidelines in creating your own PCBs.

Before you get started, it is a good idea to level your bed  and consider using anti backlash nuts.

Engraving

Getting the most precise results from your Mill One for creating traces relies heavily on your feed rate. The faster the gantries move, the more deflection can occur during changes in direction. With larger traces or traces that do not need to be very precise, a speed of 600mm/min to 800mm/min is appropriate. For small, high precision traces, set your feed rate to around 300mm/min to 500mm/min. Using a higher spindle speed is typically better, however you can still get very good results when using the lower speeds on your router.

Drilling

Drilling for through hole components is fairly easy, and since the drills are very small, very little force is needed to drill holes in PCBs. Feed rate and spindle speed settings do not make a noticeable impact, however a slower plunge rate of around 100mm/min to 200mm/min will make sure that your drill bits do not break.

Cutting

Once the PCB has been engraved and drilled, it can be cut to shape on the Mill One. At this point, you will need to make sure that the material is secured firmly to the bed since any shifting will ruin the part. Small end mills work well, something around 2mm is recommended. A depth of cut of around 0.75mm and a feed rate of 600mm/min is a good place to start, but you can increase your depth of cut if you have good work holding on your part.