CNC Router

CNC Machining refers to a type of machine-controlling tool that allows to program an manipulate machines with a defined purpose: removing from a base material in order to create new shapes. A CNC machine can convert wood, plastic, steel, glass, etc. into a desired object with ease.

A CNC Router is only one of many types of CNC machines. The Router consists of a mounted base with mobility in 3 (sometimes) 4 axis, and a drill bit that´s used to cut the material. Unlike a Laser Cutter (like seen in week 3), a Router can cut thicker and larger material, allowing the user to maker bigger pieces in the end.

The Assignment

This week´s assignment required us to create “Something Big”. Furniture was a no brainier, as it is not only big but also really achievable with our available material: 12mm Plywood.

I´m a foreign student, so I rent a decently sized apartment with a friend of mine. I decided that this week´s product will solve a problem we´ve been having since day one: I decided to build a TV stand!

The (Risky) Plan

My plan was to create a TV stand for my living room. This TV stand would have assembling pieces to create it’s structure and would be designed from scratch by me. Plus, I decided to go the extra mile, by incorporating material bending into my design.

I wanted to add a 180° turn into my design. This is often considered an advanced woodcraft technique, but in reality comes down to a couple of key steps that, if done correctly, will result into a beautiful final piece.

The Sketch

Firstly, I designed a quick sketch in a white board on how my TV stand will look:

On the top left of the whiteboard there is a quick sketch on how I want my TV Stand to look. As you can see, there is a 180° turn in the material. The design includes some supporting bases for stability, as the TV will be placed on top of it. Plus, some legs to prevent scrapping in the bottom of the stand. On the right side of the white board, there is a preview of the main part of the TV stand body. The piece is divided into 3 sections, two of which correspond to the top and bottom faces. The third face is where our bending technique relies (more on that later). Plus, there are some simple math calculations to better visualize the values I will be working with.

The Kerf Bending

Kerf Bending refers two a technique that involves a series of cuts in the material you desire to bend in order to achieve the necessarily structural imbalance on the material for it to bend. With some calculations, your material will be cut in a way that, with caution and some other tricks, can bend into your desired shape.

First of all, we need to calculate the radius of our bend. This is quite easy, as our 180° bend results in a circle shape. Using the circle perimeter formula and dividing it into two (as we only need one face) we can calculate the perimeter:

Then, we must calculate the number of cuts we need to make into our material in order to achieve the bend. To do this, we must divide the resulting radius between the drill bit diameter:

At last, we must determine the deepness of our cut. This doesn´t require a strict calculation, as leaving between 1-2mm of material is the standard. For our 12mm thick Plywood, cutting 10mm deep for each line will be enough.

Designing The Furniture

For this project I decided to use AutoCAD again. In previews weeks I shared my discomfort using AutoCAD for parametric design. But in this case where fully parametric design is not needed, AutoCAD will help us make our design faster than with my go-to CAD software: OpenSCAD.

Booting up AutoCAD, my first task was designing the main body. With some measurements I got from my current TV stand arrangement, I built the top and bottom bases. Then, with my perimeter calculation, I built the to-bend segment in between.

Now was time to add the kerf bending lines to the corresponding segment. To to this, I calculated the distance between each line, and used the OFFSET tool to create them.

After that, I started building the supporting bases:

Note: You will notice that this designed uses a lot of lines for the kerf bending section. This was because my calculations where wrong at the beginning. The formulas explained above are the correct ones.

In order to join our supporting bases I went for a mortise and tenor pattern. The tenor part was made 1mm bigger in size in order to better accommodate for the actual cutting. In the end I ended up with this amount of supporting bases:

• 2 small supporting bases to the sides (the ones already shown).
• 1 big supporting base in the back of the stand, with some cable holes.
• 2 small supporting columns for the front, to serve as both extra support and style.

At last, I created 3 separate layers for each type of cut:

• A red “profile” layer for the outside of each piece.
• A blue “kerf bending” layer for the kerf bending cuts.
• A yellow “inner” layer for everything that will be cut in the inside of a piece.

I also made some annotations on every key dimension of the build. It´s not meant to be pretty, is meant to be a record of my sizes for future recalculations and reproduction of the piece.

Aspire

The CNC Router itself is not able to interpret .DXF or .SVG files itself. You need to convert your design into GCODE, which is a series of steps the Router will read. it´s like telling it exactly how much steps to take in any direction and in what order. AutoCAD cannot export our design in GCODE, but luckily for us there are programs that will not only help us to create this needed file, but also prepare our design for the cutter.

Aspire Vectric is a CNC modeling software, designed to help you create, prepare and visualice anything you want to cut with your Router. To use Aspire, you can download it´s free version from their official page. The free version is enough to do almost anything we need to do, but there is one big step we cannot do with this version, more on that later.

Opening Aspire for the first time, we must create a new file. Once in our new file, the program will ask us some key values of our project in the left side of our screen:

For my specific project, I selected the following parameters:

• A Single Sided job type.
• 122mm Width and 240mm Height.
• Material Surface as Z Zero.
• Bottom Left corner as XY bottom.

Now, in Files > Import as Vector… we can import our .DXF file from AutoCAD:

Now, we can change tabs by closing the Design menu on the left side of the screen and opening the Tool-paths menu on the right side of the screen.

We must select the “Profile Path” option (the very first icon) and configure our 3 types of cut: The profile, the “indents” and the kerf bending. To do this, we can simply select the “Profile Path” option:

A menu will appear with multiple options. The first thing wee must select is the actual path. To to this, go to the “Select…” button and choose your desired layer. Make sure to select “Closed” or “Opened” vectors as they apply, and the “Associate with toolpath”. Now, we can configure the rest of our path:

For the “profile” layer I went with:

• Default Cutting depth (12mm).
• 1/4" Standard Mill Tool.
• Machine Vectors on the Outside.
• Added Tabs (Selecting the “Add tabs” menu, Edit Tabs > Generate Tabs).

For the “Indent” layer, everything stayed the same, except:

• Machine vectors on the Inside.

And for the “Kerf bending” layer, I went with:

• 10mm Cut Depth.
• 1/4" Standard Mill Tool.
• Machine Vectors On.
• No Tabs.

Note: This setting are not the norm, and you can experiment with them.

After that, a 3D preview of your cut will appear in screen. if everything seems correct, click the “Close” button on the “Preview Toolpaths” menu.

Now we face a big problem. This last step involves exporting our Paths into the GCODE for our CNC Router Model. Sadly, the free trial version of Aspire won´t allow us to export GCODE, meaning that our design cannot be completed using only this software.

VCarve Pro

In our Lab and some computers on our university, there is a software called VCarve Pro that will solve our problem. VCarve Pro is the exact same software as Aspire, but without 3D rendering capabilities. Once our design is completed in Aspire, we can easily export it into one of this computers with VCarve Pro installed. To do this, go to Files > Export as… and save your project as a VCarve Project file.

Now, open your project in VCarve Pro, and export the .GCODE file. You will be asked for a CNC Router model. In your group assignment page there must be the exact name and model of your CNC Router if you are unsure. Still, your Lab´s computer should already have the Router model already available to use.

Now, with our GCODE file in an USB, we can begin using the CNC!

Using the CNC Router

Our university has two available CNC Routers: A Mach 3 and an Asia. I had to use the Mach 3, as most of my classmates wanted to use the Asia and spaces where already taken. I was already at a big miss advantage, as our Lab´s safety training and usage lesson where given on the Asia, with just a brief overview of the Mach 3. And, most importantly, I have never used a CNC Router before.

Still, the basics of using the Asia Router still applied to the Mach 3. First of all, we must start up the Router with it´s on/off switch. The Mach 3 is computer-controlled, so there is no dedicated physical emergency stop button, but this switch can be used as so in case of emergency.

Opening the Router´s software for the first time, it looks like a spacecraft. For whatever reason, the UI seems to be misplaced on this computer. Everything I needed was there, but it was disorganized. Looking at this software for the first time, it was quite intimidating…

With a YouTube video I was able to identify the manual control emulator of the Router. By typing TAB on the MDI tab, you can access this control to move your Router to your desired position:

After the Router to your desired starting position, you can click the Zero buttons for each axis (x, y, z). We established that our Z Zero was going to be the material surface, so our drill bit was meant to be placed on top of the material. Using a Slow Jog rate in the controller emulator, I was able to place the drill bit right on top of the material.

Now, with our zeros ready to go, we loaded the GCODE into the software. Our design was ready to be cut! I clicked the start button. And then disaster struck…

Something went Wrong…

The drill bit (without spinning) pierced itself into my plywood and then proceded to move. Even though the drill bit was stuck, the machine kept moving forward, applying pressure to it until it exploded. In a matter of 2 or 3 second, I the drill bit was broken. I wasn´t even able to react on time. By the time I hit the emergency stop button, the damage was already done.

I have a few theories on what went wrong:

1. I was meant to get the drill bit to spin before starting the cutting process.
2. I placed the zeroes of the machine in the wrong place.
3. Something was not correctly configured in Aspire / VCarve Pro, like forgetting to add the Z Zero on the material.

It was a lack of proper training and experience plus one or many mistakes from my end that resulted in a failed attempt at using the Router. There was a spare drill bit available, which was great news for everyone else that was scheduled to use this Router, so I was tasked with replacing it. But after everything was done, my time to use the Router was over, and I wasn’t able to cut my pieces.

A Lesson on Failing

Failure is the greatest teacher. One day, some of you might encounter yourselves in a situation similar to mine. It is natural to feel upset and discouraged from the experience. In the end, the only thing broken was a replaceable drill bit. As long as no one gets hurt, life goes on. Prices are paid, pieces are replaced. And most importantly, now that we now what not to do, we can regroup and go back to the Router once again. The FAB Academy is meant to be a learning experience, and with learning comes failure. Getting up and trying again is the only way to get better at something.

Files