CNC cutting is rapidly becoming my drug of choice. The shear beauty of the finished pieces as they come off the machine is addictive. But getting here was a long and windy road...

To CNC or not to CNC? That is the question.

I’d been thinking about purchasing some sort of equipment to produce high quality custom components for a while. Everyone was raving about the 3D printing revolution and the chaps at Flite Test were pumping out kits from their laser cutters at a rate of knots.

A CNC cutter seemed the obvious choice. I could cut a variety of components from a variety of materials. They are fairly quick and relatively economical to run.

A short DHL shipping later and my CNC3040Z was unpacked and sat on the workbench.

Setup woes…

The first thing I have to say is that the machine is lovely. The quality is excellent and the fit and finish of the parts are really nice. A little bit of assembly is required to attach the stepper motors to the screw drives but that is about all I needed to do.

I was really excited to get started so it was frustrating to say the least that I then went through anything up to a month of fiddling and head-scratching to get the thing running.

There are a number of modern CNC machines that are USB driven but these tend to be higher end kit. Most machines out there seem to be, like mine, driven by a serial connection. If you are considering going down the same route, here are a few things you need to bear in mind:

• You will need to buy software to create your toolpaths and GCode as well as software to actually “drive” the machine.
• You will need to be running a 32 bit version of Windows (not sure about Macs).
• You will need a proper serial port to plug it into (USB to serial adapters don’t work).
• It won’t run off a laptop, so you’ll need a desktop running all of the above.

Other things you’ll need…

Of course, if you want to do any serious cutting you are going to need a good stock of router bits. The shape of these change depending on what you want to do with your machine but as I was only interested in cutting out patterns I went looking for an array of end mills.

Sacrifice board

If you are cutting “slots”, that is full thickness cuts to create something like a multirotor plate, than you will need to protect the bed of your machine. A sacrifice board is a level surface, preferably of softer material than what you intend to cut, that can be clamped beneath your workpiece. I’ve tried a number of things but have found either foam board or simple MDF to be the best solution.

Software Choices

There are a number of different bits of software you will need to get your ideas from inside your head and onto your CNC machine. From what I can tell this will include (as a bare minimum):

• Some sort of design/modelling software to visualize your design on the computer.
• Some way to build your toolpaths and generate the code to drive the CNC machine.
• Software that actually “drives” the CNC machine.

I’m still not entirely sure what some of this software does and I’m pretty sure there will be better ways of doing things but I’ll take you at least through how I do it.

3D Modelling and Blueprints

I do everything in Sketchup. It used to be Google Sketchup but now it is owned by Trimble (I guess the same mob that make the Gatewing UAV). Yes, I can hear some of you groaning! I know the pros will be using Solidworks, Autocad or other more advanced tools but I know Sketchup and I find it easy enough to use. It also has the benefit that when I am working with others to produce a design, Sketchup is accessible and I can send files around easily.

Once I have a workable design I use the “Flattery” plugin to export my drawings as an .svg drawing. The good thing about using .svg is that all dimensions and vectors are saved perfectly ready for the next step…

Vector Conversion

My toolpath software can only accept certain file formats and I can't go directly from Sketchup to CAM, so I have to convert and clean up the drawing first. Fortunately I run a copy of Adobe Illustrator for work and this is ideal for the job. Opening the .svg file in AI reveals a number of additional hidden vectors so I delete those, increase the line width slightly to 0.1mm. Rotate the shapes how I want to cut them and then save as an .ai format vector image ready for the toolpath creation…

Toolpaths (CAD/CAM)

I saw Vectric Cut2d recommended on a YouTube video and took a look at the software. There were more complicated and expensive options (such as their VCarvePro software) but Cut2D seemed to do all of the things I wanted so a short credit card swipe later and it was on my desktop.

The software itself is easy to use. It is actually a simple CAD program in its own right and the interface makes it easy to import and manipulate the .ai files. One thing I did learn was that once the vectors are loaded it is a good idea to select everything and hit ctrl+j to close all the lines and make selecting paths easier.

CNC Motion Control Software

The manual that came with my machine stated that it was designed to work with Mach3 Mill from Newfangled Solutions, so that is what I got. I am pretty sure that I am still not using this software to it’s full potential but it really is a complex bit of kit.

In a nutshell it takes the G-Code from the CAM software and sends it in real-time to the CNC machine through a serial cable. It is this software that tells the motors how many “steps” are in a millimeter and how fast to spin the drill and move the gantry. Everything starts and stops here so it pays to read the manual and at least learn the basics.

Toolpath Time!

The toolpath is where the fun really begins. There is absolutely no way I will be able to tell you how to design toolpaths in one article but I will give you some of the things I have learnt along the way…

The first thing to do when you open your CAM software (I am using Vectric Cut2D remember?) is to tell it the size of the blank plate you will be working with. I generally use either a 250mm x 200mm or 400mm x 200mm blank. You also need to tell the software how thick your material is as well as where “home” is so it has a point to work from.

The next thing to do is to actually import your AI drawings and arrange them on the blank.

Once all your plates are in place I found that in Cut2D I needed to select everything and then hit CTRL+J to close all the vectors. This means that if I then try to select a plate outline for example it will select the whole thing rather than a single segment.

Toolpaths are created by first selecting everything you want to cut and then choosing a path style from the menu. For this type of cutting I use either drill or profile. Drill is usefull for the smaller holes whilst profile is the path to use for everything else.

Never try to cut a whole design in one toolpath. By breaking it up into different parts it is easier to monitor and check progress as well as use different size end mills for different components.

Once you have created your toolpaths you need to export them to G-Code. You can add more than one toolpath to a G-Code file but I like to keep it simple and save each one separately. The output I use for my machine is “G-Code Arcs (mm) (*.tap)” and to look at is nothing more than thousands of lines of numbers and letters.

Let’s get on with it then…

So, we’ve got our design and we’ve got our toolpaths, now we need to get the thing cut. Here is pretty much how I go about every project…

Preparing the blanks

I think I already mentioned that I use one of two blank sizes. The smaller size is 250mm x 200mm and this fits most miniquad size frames. The larger plate is 250mm x 400mm for the larger frames.

The sheets come from the factory in 500mm x 400mm sheets and I cut them down with a hand-held circular saw with a thin 40 tooth blade. I cut the plates down in this way for a couple of reasons:

1. My CNC machine isn’t that big so I couldn’t fit a full size sheet on the cutting bed if I wanted to.
2. It is easier to work with smaller plates and creates less waste if I cut one frame per blank.
3. Using the thinner materials, larger plates can bow and vibrate causing problems with cut depth and deflection.

The next thing I do is stick the blanks to the sacrifice boards. As most jobs use both 1.5mm and 3mm plates I stick one of each either side of the sacrifice board.

Hang on. You “stick” the blanks to the sacrifice board? (I hear you ask)

I spent a long time trying to work out how I could cut components without having to have nasty tabs all the way around the edge. In the end I settled on actually fixing the blank plates to the sacrifice board using spray adhesive. The image shows early tests using foam board blanks but I have since moved to MDF blanks as they are both cheaper and stiffer. Here’s what I have learned:

• Cut a piece of 3mm MDF to the same size as your material blanks
• Leave the protective coating on your material
• Spray one side of both the MDF and the material with spray contact adhesive and press together
• Put cutting material on BOTH sides of the MDF. This reduces waste and also adds a lot of stiffness to the surface to be cut. If you are using two thicknesses of material (e.g. 1.5mm and 3mm) put one of each on your sacrifice board and cut the thinner material first to maximise the stiffness.

The last thing to do once your blanks are stuck is mark the centers by drawing a line from corner to corner over the protective coating.

Clamping & Setting Up

My machine was supplied with four screw type clamps that can be moved anywhere around the cutting table by way of square nuts that lock into the channels which run full length.

I marked a straight line (with a set square) across the bottom of my table so I had a datum from which to align my boards and then use the screws clamps on each corner. Alignment is important if you are trying to maximise cutting areas and minimise waste as you don’t want your tool to slip off the edge of your material during a cut. I find that by having the second thicker sheet on the back of the sacrifice board I can clamp right on the corners and still not see any bowing in the center.

With the correct end mill securely clamped in the chuck I now manually wind the point into place so that it is on my center mark, just touching the surface of the material. I do have an electronic z-axis setting tool that I could use but I find it just as easy to find the material surface by hand.