How to Set the Speeds & Feeds for Your CNC Projects

In this Instructable, we are defining what the term "speeds & feeds" mean, and looking at how to set these parameters for your CNC projects. Makera is a manufacturer of high precision and easy to use desktop CNC machines, as well as a company built by makers, for makers, in the era of makers. This Instructable is intended to guide users of all levels through getting started with CNC machines, specifically by looking at crucial settings for CNC production techniques.

While we are discussing settings compatible for the Carvera Desktop CNC or Carvera Air, similar concepts are applicable to a wide range of CNC mills or routers, suitable to different resources that you might have available. And while we are defining key terms and techniques in this article, you can find our full Speeds & Feeds guide on our Wiki Site here.

In addition to writing and sharing how to select the right Speeds & Feeds in this Instructable, we've also created a YouTube video as part of our Getting Started with CNC Machines series for additional information and support.

For additional information, support, and resources, visit Makera.com or check out our YouTube Channel and Wiki Page.

For this, you need a CNC machine, materials, and bits of course! As mentioned earlier, these concepts are applicable to a wide range of CNC machines, including mills, routers, and lathes, as well as with a wide range of bits and projects. You also need CAM software, which is the program that is used to set these parameters when preparing a design file, and something we are going to discuss in the next step.

There are a lot of great CAM programs suitable for CNC production techniques. The Carvera and Carvera Air desktop CNCs are compatible with most CAM programs, including Autodesk Fusion, VCarve, kiri:moto, SolidCAM, MasterCAM, FlatCAM, CopperCAM, Lightburn, and more! You can learn more about the different programs we support on the software page of our wiki site.

But if you're just getting started, we've recently released Makera CAM to be one of the most intuitive CAM programs available, suitable for users who are new to these concepts. If you're interested, you can learn how to use Makera CAM through this tutorial series and user guide.

Through this Instructable, we're going to look at what Speeds & Feeds are, how to set them, and cover key definitions and techniques to help you find success. So let's dive in!

Before we get into what Speeds & Feeds are and the different settings that need to be considered when setting these parameters, let's first cover where you might be performing this task. When you work with a CNC machine, and this goes for mills, routers, lathes, lasers, 3D printers, and so on, there are typically two types of programs used.

CAD software, which stands for Computer Aided Design, is where you design your part. CAD comes in many forms, from 2D to 3D modeling, as well as various levels of difficulty and capability. Some great CAD programs are Tinkercad, Fusion, Onshape, Adobe Illustrator, Inkscape, etc.

But before you can send your design from CAD to your CNC machine, you need to tell your machine how to manufacture it. If you're familiar with 3D printing, this is done in a slicer program like Cura or PrusaSlicer. Those programs can be considered to be CAM programs, or programs for Computer Aided Manufacturing.

3D Printer slicer programs like Cura are only intended for 3D printing, while other CAM programs such as Fusion or kiri:moto work with a range of techniques. And there are more robust CAM programs, such as MasterCAM or VCarve that are intended to be used with subtractive manufacturing methods, like working with CNC Mills or Routers. Makera CAM falls in this category as well.

By using these CAM programs, we can import our designs from CAD, then set the correct settings to manufacturing our designs successfully....which is where "Speeds & Feeds" come in. And some CAM programs, like Autodesk Fusion, combine CAD and CAM in one application. After setting your parameters and preparing your models in CAM, the exported file is typically a coded file written in GCode, which instructs your CNC machine on how to manufacture your design.

Another program that's important to identify here is the controller program for your machine. This will vary from machine to machine, unlike CAM which is typically more generic. The controller is what allows you to manually move your machine around, load a file, and start or stop manufacturing. You can typically adjust Speeds & Feeds on the fly using these controllers, which can be helpful as you monitor the progress of your manufacturing process. For the Carvera and Carvera Air, we use the Carvera Controller App to perform these functions.

Now that we've covered the programs needed to implement Speeds & Feeds, let's discuss what these settings actually are.

When we say the term Speeds & Feeds, we are referring to the settings for how quickly our CNC machine travels and cuts our material. These settings will vary based on the type of machine you are using, the bit you've chosen, and the material you are cutting.

The First thing you need to identify are the recommended parameters for your CNC. You can find our recommendations for the Carvera and Carvera Air desktop CNCs on our wiki page, as well as in the tool profiles for the different CAM programs we support. As discussed earlier, we would set the Speeds & Feeds in the CAM software as we choose our cutting tools. And you can learn more about how to use CAM and choose a cutting tool in this instructable.

Its important to understand that the Speeds & Feeds settings will drastically impact the success of your project. Setting something to cut too quickly could break a bit, or even damage your machine. As a result, we ALWAYS recommend starting on the lower end of what's recommended, and that you perform test cuts before diving into a large project. We talk more about this in our Instructable for selecting stock.

As we adjust our cutting speeds, there are a few different feed rates to consider. Feed rate is the speed at which a cutting tool moves along a workpiece, or the distance it travels in one spindle revolution. It's usually measured in inches per minute (IPM) or millimeters per minute (mm/min).

Spindle Speed is the speed that the spindle is rotating the cutting tool at, whether it be a mill or a router. Smaller diameter bits typically operate at a faster RPM, while larger diameter bits would operate at a slower RPM to maintain the same torque.

The Cutting feed rate is how quickly the machine moves as its cutting along the X and Y axis. And the Plunge feed rate is the speed at which the machine plunges, or lowers, into the stock to begin cutting in the Z axis. We typically plunge at a much lower speed when compared to the cutting feed rate.

In general, harder materials like metal require faster spindle speeds and slower cutting speeds. This will allow for bits to cut the harder material with a cleaner finish, but also avoid breaking bits during the cutting process. For softer materials like epoxy, plastics, or woods, we can increase our travel speeds but also want to reduce the spindle speed for an optimal result.

More Speed & Feed parameters to consider are your Step Downs and Step Overs. Step Down describes the distance traveled during each vertical pass, or in other terms - how much the Z axis lowers after each pass. The amount of material you can remove per pass depends on the material you are using, as well as the type of bit you're using and the size of the bit. A larger bit will be able to handle more stress than a smaller one, meaning you can remove more material per pass without worrying about breaking it. But a pointed bit, like a V-bit used for engraving, wouldn't be able to plunge into as a much material as a flat end mill either due to the size of the tip.

Step Over is a similar parameter, but in the horizontal plane rather than the vertical one. Your Step Over describes the overlap of your cut, or how much your bit moves over per pass. For example, If I was working with a bit that had a 0.125" diameter, and my Step Over was 0.125", there would be no overlap. This would result in a high amount of stress on the bit, and also a poor cut. Typically, we Step Over a distance that is between 50% and 70% of the bit's diameter, so a Step Over of 0.0875" would be ideal for a typical 0.125" bit.

Ramping is a plunging technique that changes how a bit enters the stock to begin cutting. Instead of plunging straight down, Ramping allows for the bit to enter at an angle, and typically in the direction opposite to the cutting direction.

To enable Ramping, you typically need to set the distance you would like to ramp for, the angle at which you want to enter, and how high above the stock you want to start the ramping process. These parameters can vary depending not only on the type of stock you're working with and the bit you're using, but also the type of cut you're creating. For a small pocket, you may only be able to ramp for a small distance at a relatively shallow angle. But for a contour cut along an edge, you may have more room to work with. In general a ramping distance between 5 mm - 10 mm, at an angle of 2 -10 degrees, with a starting height of 0.5 mm - 1 mm, is a good place to start.

Retract is a parameter that is specific to drilling operations. When using a drill bit on a CNC machine, you can perform a vertical drilling operation just like you might when using a drill press. And as with a drill press, its usually not a good idea to plunge straight through your material.

This is because doing so might break your bit either from excessive force, by trying removing too much material at a time, or by overheating due to a build up of hot chips. By enabling a Retract operation, the drill bit will retract during the drilling operation to gradually drill through the material while also allowing for chips to evacuate. This is also sometimes referred to as a peck drilling operation.

To enable Retract for a drilling operation, you typically have two options in addition to the other Speed & Feed settings we discussed earlier. A Fixed Retract Distance will retract to a set Z height every pass. This allows you to ensure that the bit travels far enough for chips to evacuate, but also isn't always the fastest approach. As an alternative, you could set a Relative Retract Distance which will retract a certain amount based on the depth at which the bit currently is. This will also allow for the plunge to pause and back up for chips to evacuate, but without needing to travel an excessive amount.

For softer materials like plastic, epoxy, or softwoods, you probably don't need to use a Retract, but its never a bad idea to do so. This will prevent excessive wear on your bit, as well as reduce the likelihood for failure.

For whatever settings you choose, and for whatever type of CNC machine you're working with, there are a few best practices which are universally applicable and may support you in finding greater success.

Start at the minimums. We find that many of our users start at the fastest possible cutting speeds, which may sometimes cut down on machining time, but also increase the likelihood of a poor cut and failed result. Start slow, and then gradually work you way up while keeping your settings proportional to one another.

Perform tests. We always encourage working through an iterative approach, where you test your design files and settings on a softer and cheaper material before diving into a complex project. Test your designs using epoxy tooling board, or foam, or wood, or even machinable wax first. These materials may respond similarly to another material, but without putting too much wear on your bits while allowing you to catch any possible issues early.

Buy spares. We all make mistakes, and sometimes things go wrong. Through safe prototyping and experimentation, the chances for this can be reduced, but we should still plan for this by buying spare bits, spare stock, and other wear and tear items so we aren't caught out in the middle of a project or deadline.

Collaborate and Compare. We are very fortunate to have such an active community of users working with the Carvera and Carvera Air. Through our Facebook groups and Discord Group, we encourage and support users sharing successes and failures, including recommended settings and parameters to help one another find success, and also improve our products.

Ask for help! This aligns with the practice listed above, but its important to remember that making mistakes is part of the learning process. Should you find yourself stuck and in need of assistance, contact us!

While we didn't look at every possible parameter you could set in this guide, what we covered should be enough to get you started, and hopefully finding success for your CNC projects as you adjust your settings and find the optimal parameters for the job!

More things consider which are equally as important as the speeds and feeds you choose are selecting the right bits and materials for your projects. You can check out more guides and videos we've created to support learning these concepts, along with more how to's and guides on the Makera Instructables Page, YouTube Channel, and Wiki Page.

Thanks for reading, and happy making!

Written by @MrErdreich and @Makera_Inc