Holiday Project, A DIY CNC Adventure

This past holiday break, I have mostly stayed in the garage – setting up a CNC machine and cutting all the things that I deemed cuttable by it.

Owning a CNC machine has been on my list for a long time, it is just out of my price range for a high quality professional grade machine, or maybe not useful enough for a “toy” level DIY one. But every time I built an electronic toy, like Pac-Man on a String, I wished to have a precision CNC machine to build a case for it. Recently, a casual chat with Jeremy (@jrwashley) brought up the topic of DIY CNC, I was encouraged to try to build one now, otherwise, it would just be a spot on the wish list.

I researched on the landscape of CNC, primarily focused on entry level to mid-level DIY types.  You can find lots of “CNC Routers” on Amazon, with price range of $400 – $800, but be aware that the controller is antique and requires a old desktop PC with parallel ports. You can also find many CNC DIY builds on Instructables.com, which gives you good ideas on all the elements making up the machine, but may take a while to source or custom-make the parts, with possible fitting issues of parts from difference places. Many of the entry level CNC machine can do light engraving and cutting on softer materials, but will have difficulties in precision cutting harder materials. The ready-made mid-level CNC machine can handle most of jobs better, but it could easily run over $5,000, such as the ShopBot ones.

Choose it.

The machine capabilities and quality are usually correlated to the price tags, so I have to ask what I really need, in order to keep the price in reasonable range while it can do a decent job. If you are in market for a CNC machine, you probably should think along the same lines too. Here is what I laid out:

1. Mostly work with acrylic and plastic materials, some decent-size wood work, and occasionally aluminum sheets;
2. Good size of work area for a desktop/bench-top, from 10′ to 20′ in X, Y axis;
3. Want to have solid structure to ensure the precision and strength of cuts, and the durability of machine itself;
4. Controller is less of a concern for me, as I will likely replace it later with my own experimental controller, but I do want to have it work with my current computer instead of going back old parallel ports;
5. Controller, CAD and CAM software; capability and open source?
6. For now, I want to have good capable CNC machine that I can use immediately, instead of figuring out how a CNC machine is built. So that I can learn to operate the machine, without complication of build issues. After that, I may come back to make a inexpensive DIY CNC machine or other installation from such control mechanism.

With above considerations, it is clear that I would get a kit where all parts come from the same vender (so no mis-match), but I still get the chance to look at all the parts (to understand the purpose of all the parts), and to assemble all the parts into the machine (to understand the machine composition). That will enable me to build my first CNC machine with less potential problems (also to isolate machine issues from operation issues during learning stage), while still get the great ins-and-outs of a CNC machine that I can potentially design my own version in the future. Two equal candidates surfaced: Shapeoko 3 from Carbide 3D, and X-carve from Inventables. I like Inventables for it is an open system and has great resources, but the solid XY rails of Shapeoko 3 won out.

Build it.

If you have prior experience in assembling a CNC machine, the Shapeoko-3 kit may take you several hours to put it together. For me, I really took it slow to examine each part and understand why and how each part is designed, and how the part will function in the final machine.

The controller works as taking G-code commands from your design, and moving the router along X, Y, Z axis precisely to make the cuts. The controller board can be replaced if I want to do further experiments, by using an Arduino running Grbl.

Operate it.

The basic workflow from idea to build:

1. Sketch up on a napkin 🙂
2. Transfer your drawing from napkin to a CAD (Computer-Aided Design) program, where you do the engineering or artistic design,
3. Export the CAD drawing and import to CAM (Computer-Aided Manufacturing) program, where you do the specification of material (type, size, thickness, etc), mill bits (type, size, etc), operation parameters (feed rate, plunge rate, step depth, routing path), and tool-path and cutting order. You should image how the machine would cut from start to end because that’s exactly what you do here to instruct the machine from start to end,
4. Generate G-code from CAM to be fed to CNC controller software,
5. CNC cutting or milling exert forces to cut through material, so make sure to hold your stock material securely and take safety precautions,
6. Start the job and observe – various issues may occur if you are a beginner and doing experiments,
7. If everything goes well, you get the job done. Polish it up, such as cleaning, sanding, buffing, etc.

During the first week, I ran into a lot of issues at step 6, and I had to hit the emergency STOP. During the job run, that’s when all the parameters / factors come together, and you have to experiment to find the perfect combination of operational control parameters, for your design on a particular material using various bits for engraving, milling, cutting. It is a large number of different combination, and experience will definitely help.

For example, not all acrylic materials are equal – generally cast acrylic is good for cutting and even milling, but extruded acrylic tends to melt and form a blob at the bit head. You may slow down spindle and increase feed rate to reduce the rubbing, but it could break milling bit if you go that direction too much. You may use larger bits on wood milling (and later sanding and polishing), but probably it is better to do engraving on acrylic as milling may dull the luster effect.

Usually some CAD/CAM software should come with a CNC machine, whether it is free or paid, open source or propriety, to get you started. But after you get a handle on the CNC workflow, you should explore different software packages for CAD and CAM, as different software can provide various capabilities required by your design.

Show samples.

First set of successful cutting and engraving on acrylic:  1. Abstract flower; 2. Spring time – little girl, kitten and butterfly.

After experimenting for almost one week, I perfected the operational parameters (spindle, feed rate, plunge rate, material, cut/engrave/mill) and proper bits (bit size, bit shape) for making a batch of gifts for the AppsLab team:

As apprentices in the OAUX organization, we all know UX design philosophy: Glance, Scan and Commit. And that is represented in this CNC-cut fashion of elements:

If you still remember from high school chemistry, they are elements from periodic table: Gallium (Ga for Glance), Scandium (Sc for Scan), and Curium (Cm for Commit). Here is a closeup look at the Gallium with information of element symbol, name, atomic number and atomic weight:

Yeah, engravings on acrylic look better under light. Should I mill a wood-channel and install a LED strip for the display?