CNC Woodworking Deep Dive with Kenji Larsen
Kenji Larsen is a technologist who helps companies to scale prototype processes. He’s worked in fields, including robotics, cryogenics, automation, as well as consumer devices — and of course, woodworking. To say he’s a power user is an understatement, and his passion for making is infectious. Lately, he’s been using multiple Bantam Tools Desktop CNC Milling Machines in his shop to manufacture wooden parts. We sat down with him to learn more about his best practices, material considerations, and more when machining wood using any CNC machine.
Tell us more about your background. How long have you been in woodworking?
I’ve been doing woodworking for as long as I can remember. When I was six years old, I started to learn how to carve small parts out of twigs using a whittling knife. Joinery came later, and from there, most of my woodwork was carpentry and furniture projects. And while I had thought I already knew a lot about woodworking, I learned even more when I entered the world of violin restoration. It’s truly an alchemical approach to wood, structure, form, and function.
How did you get into CNC machining?
I got into CNC machining by way of software. I was working with simulation software to model tool collisions with workpiece, fixturing, and machine, back when 3D modeling was still relatively new and G-code was written by hand.
I was involved with machining turbine blades for jet engines, which are complex 3D shapes machined out of hard, single-crystal metals. That experience taught me a lot about complex robotic axis control, as well as subjects like coolant, lubricant, cutting inserts, rake angles, chip management, and surface resolutions using ball end mills. Ultimately, the mechanical challenges were far more interesting than the software ones because they present a new problem every time — it’s wonderful.
What about desktop CNC machining?
Desktop CNC machining entered the picture about 10 years ago, and even more so in the three-axis world with the proliferation of Arduino and the release of Grbl. That allowed me to put more robots in my shop, which included small CNC machines. Compared to industrial CNC machines, there are completely different concerns with real estate, process control, waste management, noise management, labor, and many other variables when working with a desktop CNC.
It enables a totally different kind of business. I don’t run a machine shop. Instead, my shop is concerned with prototyping many different kinds of technology, and desktop CNC enables fast turnaround, while producing complex, high-strength parts in a variety of materials. It’s perfect for a business that needs to rapidly iterate prototypes.
How does having a handful of Bantam Tools Desktop CNC Milling Machines at your disposal influence your workflow? What other fabrication tools do you have in your shop?
I have a number of purpose-built machines that have larger build volumes but lower precision, smaller machines with higher precision, and others with taller part-height capabilities. I have machines specially tooled for specific materials, many of which require special handling with respect to dust mitigation and lubrication. The broad spectrum of machines means I can choose the right machine for a particular job.
For instance, I have 3D printers (both FDM and SLA types), a laser cutter, manual mills and drills, a press, welding equipment, a plasma cutter, and general equipment like routers and saws. I also have a large number of hand tools. I love hand tools, especially with wood.
But the one thing that this arrangement does not have is standardization. Each machine or tool has its own caveats and software. The Bantam Tools Desktop CNC Milling Machines have helped me streamline a lot of processes and standardized platforms with software that make it easy to move a job to a different machine. This drastically reduces individual set-up time, which means more time cutting. Also, the build volume is quite large with respect to the total footprint of the machine, so it’s amazing to be able to fit four machines on one table and see three of them cutting while one is being set up.
What safety tips do you have for Bantam Tools Desktop CNC Milling Machine users who are new to woodworking?
In addition to safety glasses and hearing protection, I always recommend wearing an N-95 dust mask so you don’t breathe in dust. With woodworking, this is so common, and to constantly be breathing this dust in isn’t good over the long-term. I’d recommend using one with an exhaust valve so you don’t get tired of wearing it.
It also goes without saying that you should avoid smoking or having any source of ignition near your CNC machine when milling. Believe it or not, airborne dust can be explosive. Also, when milling, your tool gets hot due to friction, and this transfers to the material. I always keep a fire extinguisher in my shop because with all the woodworking and equipment I use, you never know.
How do you keep your Bantam Tools Desktop CNC Milling Machine clean?
Wood dust can have a significant impact on machine performance if you don’t manage it properly. It gets everywhere, which is why understanding how to clean your CNC machine throughout and after a job is crucial. For example, use an air compressor to blow out rotating parts often throughout a job, and vacuum swarf (dust, chips). And no matter how good of a job you do, neither of these airflow methods will remove the smallest dust particles from surfaces, so build in time for wiping up this debris with dry microfiber, as well as alcohol-based wipes, where appropriate. Don’t use water-based wipes because CNC machines don’t like water.
Note: If you’re milling wood using the Bantam Tools Desktop CNC Milling Machine, please use the Bantam Tools Desktop CNC Vacuum Accessory.
I’d also like to point out that If you use computers in this dusty environment, know that your computer fan and internals will get coated with dust. Blow out and vacuum out your computer from time to time as well — or figure out how to separate the computer from your shop.
Keep a separate, dedicated waste flow for wooden swarf, sawdust, and scrap cutoffs. This includes vacuums for machine cleaning. Wood swarf is much easier to handle when it’s uncontaminated by things such as aluminum swarf.
What milling strategies would you recommend when doing CNC woodworking?
There are so many things I could dive into for this question. Honestly, entire books can be written about this stuff. Wood isn’t like metal. Wood has biological properties. As a starting point, understanding the character of the wood is crucial. This encompasses things like grain direction, compression, humidity, oiliness, fiber length, and internal strength (in various directions).
- Is the wood chippy (ebony)?
- Is the wood stringy (bamboo)?
- Is the wood both chippy and stringy (oak)?
- Is it spongy (balsa)?
- Is it stiff (cherry)?
- Is it sappy (pine)?
- How homogeneous is it?
- Are there burls and knots, or is it just a plain, clean, fine-grained span of wood with straight, parallel grain lines?
All of these questions go through my head as I’m selecting and working with a certain type of wood. I know it’s a lot, but once you understand the character of the wood, you can make decisions about how you’re going to fixture it and how it’s going to behave when cutting.
For example, in a highly compressible wood, it may be advantageous to choose a piece of stock considerably larger than the part you want to end up with because you can fixture the edges of the stock, and most of the compression will occur along the outer edges of the stock, leaving the central portion (where you’re cutting your part) decompressed.
Also, keep in mind that wood shrinks and expands due to temperature changes. For instance, in winter, parts will be smaller and in the summer, they’ll be larger. Long after cutting, this may have an effect. If you’re making blocks, it might not matter so much. But if you’re making thin plates, they may not stay flat, and if they have notches, the notch width can vary.
The key is to design your parts with built-in tolerances to accommodate for this variation. For example, wood heats up as it’s being cut. It might expand and warp on the machining bed. It might bow a little. Ask yourself: Can my part withstand a Z error of half a millimeter just in the middle? Maybe! Design for it!
Your CNC machine is just one of the tools in a chain of tools to make your wooden part. There will always be a post-process and often several pre-processes. Unlike a metal part that might come off the mill completely finished, it’s rare for a wooden part to be immediately ready to use.
How do these differences influence the decisions you make in terms of tooling selection and speeds and feeds recipes?
With materials such as aluminum, steel, ceramic, and plastic, you can come up with a spindle speed and feed rate combination that consistently works based on results like surface finish. Once you have a base recipe down, you can dial them in depending on the operation and material you’re machining.
But with wood, you have so many other variables to consider. Wood has lignin, which melts. It also contains cellulose, which burns. It may contain sap and it contains water, which not only facilitates heat transfer, but also evaporates. You also have grain direction, overall size of the grain (wide vs. fine, with respect to the size of the tool and the distance between flutes).
Trees grow slowly in the winter and fast in the summer. This is what leads to the rings you’ll see. In cut wood, the dark lines of the grain are the winter growth, the lighter areas in between are the summer growth. Winter grain is stiff and dense, while summer grain is lightweight and spongy. These grains absorb and expand differently with heat and humidity, and they respond to mechanical stress, like the speeds and feeds you use when machining, differently. As a result, there is no magic formula for wood, and the speeds and feeds recipes you use for one wood-based project will vary more than the recipes you use with metals or engineering plastics.
Aside from the Bantam Tools Desktop CNC Milling Machine, what are three tools you can’t live without?
I tend to make tools for specific purposes. The Bantam Tools Desktop CNC Milling Machine is actually great for fabricating parts for the tools I need!
But aside from that, my top favorite tool would have to be my violin knife. It has a thick steel blade, center-hardened, and a cutting edge with a shallow curve, hollow-ground. It’s perfect for any job requiring human judgement in a manual post-process. I rarely use it on violins, but more often I use it to deburr an HDPE part off the mill or shave down a non-compliant piece of wood on a part.
My 3D printer is next on the list. In general, it’s great to be able to make parts with complex morphologies, with internal structures you cannot otherwise produce. But for woodworking, it’s a perfect tool to use in conjunction with the Bantam Tools Desktop CNC Milling Machine. For example, I use the 3D printer to fabricate clamping jigs that have differential collapse zones to precisely put the pressure where I want on a wooden part that I’ve machined using a CNC. It really opens up the door to making complex wooden parts that aren’t always based on planes and corners and the 90º angle.
The third tool is a close call, but I’d have to say the bandsaw. The ability to shape stock or trim excess before sanding — in an open format with wide inspection angles — makes it a very versatile tool.
Note from Bantam Tools
About Kenji Larsen
Kenji Larsen is a technologist who helps companies to scale prototype processes, and to develop components, devices, and software to production levels. He draws many bodies of craft knowledge, and combines them with data driven analysis, to promote rapid and successful development of new technologies and techniques.n Recent activities have been in the fields of robotics, cryogenics, automation, as well as consumer devices — and of course, woodworking.
At Bantam Tools, we manufacture CNC machines with professional reliability and precision. We empower people to push the limits of advanced manufacturing and build their skills.
