CNC Machining with Blender
By Michael Kersey





In this guide I will walque through the stages of modeling in blender and bringing it to life using a CNC Mill. This guide ONLY covers 2.5D cutouts. Full 3D CNC will be covered in a later guide if there is enough interest.


Before you start

Now some of you will be thinking as you read this, “Why the hek que don't you use an open source CAD program instead of all thisí!?” The answer is simple really, people wanna know how, and I am providing one possible methodology. 'Nuff said? This guide is going to assume you are very well versed in Blender itself. If you are a novice, I assure you, this will be Gr33que to you. Well, before you get to the point where you are maquíng some kewl guy thing-a-ma-jigs with your CNC machine, you’ll need to start at the basics. Blender does not lend itself to CNC very well as that is not its intended function. It’s just something else you can do with it, if you want to invest the money and time. Money? Ya, Blender may be free, but CNC isn’t. So before you delve into this guide, you can expect to forque out no less than $500.00 to get the bare bones minimum.

A CNC Mill or Router can easily be built and there are dozens of sites with plans for CNC Routers and schematics for CNC controllers, etc, etc. In addition to your hardware, you’ll need software. Yes, Blender isn’t going to run your mill for you. I don’t want to dwell too much on the costs, but thought it prudent to give fair warning before you read through this guide and realized that you can’t afford to get into CNC. So, I will just list the components you will need:

Blender: FREE!
Your modeling software! (With a few free plug-ins to fill out the edges.)

CAD software: (Computer-aided Design)
$0 – $1,000+
A program capable of converting Blender exports into something a little more usable (a lot more on this later). In this guide, I will be using Accutrans for the CAD portion.
Recommended software: Accutrans - http://www.micromouse.ca/


CAM Software: (Computer Aided Manufacturing)
$50 to $1,000+
CAM software is the middle ware between the CAD world and the manufacturing world. In a nutshell, CAM software translates the object you have created (dxf file) into machine code called G-Code. G-Code defines the Mill/Router/Lathe’s toolpath which the machine will use to create your object.
Recommended software: SheetCam - http://www.sheetcam.com/
Cut3D - http://www.vectric.com/WebSite/Vectr.../c3d_index.htm
MeshCam - http://www.grzsoftware.com/

CNC Controller software: (Computer Numeric Control)
$0 - $1,000+

CNC software takes the G-code you have generated, and ‘talks’ to your machine. It is the interface between your computer and your CNC Mill/Router/Lathe
Recommended software: Mach3 - http://www.machsupport.com/

CNC controller:
$50 (building your own from a schematic) to $10,000+
This is the device that translates the G-Code being fed to it by the CNC Controller software into pulses that the Stepper motors or Servo motors use to physically move the machine’s cutting device.
Recommended: Xylotex - http://www.xylotex.com/
Geckodrive - http://www.geckodrive.com/

Various schematics for maquíng your own - http://www.discovercircuits.com/S/stepper.htm

CNC Machine:
$250 to $500,000+
Here, there are so many choices it is mind boggling. Mills (Generally used on Metal), Routers (Generally used on woods and softer materials) Lathes, Laser cutters, Plasma cutters, Sewing machines, Engravers, Plotters, Abrasive Waterjets and even 3D printers! Most people who are building there own CNC machines make CNC Routers. There are dozens for sale that are relatively inexpensive and hundreds more plans to make you own from scratch.
Recommended: Build it yourself!

http://buildyourcnc.com/
http://www.cnccookbook.com/
http://www.cnc411.com/
http://www.cncfuture.com/
http://www.cncinformation.com/
http://fabathome.mae.cornell.edu/

So, now that you have an idea of what you are getting yourself into, and you’re still determined to proceed, then good for you!



Modeling

There are two distinct approaches to modeling when it comes to CNC. 2.5D and 3D. 3D is easy enough, a 3 dimensional object that is cut from a solid blok que of material. 2.5D is more inline with Engraving machines and Waterjets. In 2.5D the object is more to ‘cut out’ than to ‘Carve out’ the object. Since it turned out to be far more difficult for me, and it is what I was after with my CNC machining, I’ll cover 2.5D first. Trust me, after 2.5D, 3D is a cakewalk.


2.5D Modeling

For the intent and purposes of what I was trying to create with my CNC Mill, I will explain 2.5D modeling in blender from that point of view. This is by no means a definitive guide to the limit of all the possibilities, so feel free to let your noodle wander as you are reading.


So, let’s say…


You wanted to cut something out of a piece of metal shaped roughly like the above image. For the point of illustration, we will use a sheet of 1/16” aluminum as our material. Now, I’m sure all my fellow Blender fanatics out there would scoff and say, “Hell, I could model that in under a minute!” Not so fast hot shots, remember the goal… I will repeat this until you are absolutely sik que of hearing it. Blender is NOT a CAD program. Hence, when you are modeling something in blender with the intent of using it in a CNC machine, you need to let go of several preconceived notions about ‘how to model’. When modeling for the purpose of a 2.5D CNC object, you need to concentrate more on how to tell the CNC machine what you want it to do, than maquíng the part in 3D, and then figuring out how to go from there. (I made that mistake)

The object is best thought of in this case, just like it is, printed on a piece of paper. How would you cut it outí Well, you would use a pair of scissors or a Xacto knife and cut around the edges, right. Good. Now you are starting to follow me.
In Blender, what you are trying to create is not so much the part itself, but the toolpath required to cut it out. Relax, it’s easier than most things people do in Blender!

First you need to take your picture, and put it in as a background image in the Blender 3Dview. Like so:





Now, we are going to create an ‘outline’ of the object that will be translated into the toolpath for your CNC machine. To start, create a simple circle [SPACE → Add → Mesh → Circle] in the top view [Num 7]. And scale [S+X and S+Y] it on the X and Y axes so it roughly matches the outer edge of your object.



Now, for parts that are that are going to be symmetrical in nature, it is imperative to make sure as you are modeling that you keep your vértices aligned. Instead of grabbing each vertex and putting it in place, grab them in pairs. One on each side, and scale them along the axes into place. I.e. [S] to scale, and then [X] to constrict the scaling function to the X axis. The X and Y axes should be the only ones being utilized in the top view. (There is a method behind the madness here, using the top view will save you time during the later steps when converting this to the final product.)




Scaling along the X axis

For the non symmetrical áreas, it isn’t as important to be ‘dead on’ but, if you want the final product to be as pristine as it can be, always move the vértices using the axis constraints.



You’ll find in most objects you create that there are straight pieces that are difficult to get perfectly straight, in these cases, use of the Transform Properties [N] will really speed along your modeling. First, note the vertex location on what ever axis you are trying to make a straight line on.





In this Example, the vertex is at 1.992 on the Y axis. So, grab another opposing pair… Note: Only grab two vértices at a time when using this method. Remember, when more than one vertex is selected in edit mode, the Transform apply to the Median of ALL the selected vértices.


Now that you have them, move them quickly into place by changing the Median Y to the Y axis of the first vertex. In the case of our example, 1.992.



*poink*
Your vértices pop perfectly into place!

So you have the basics, wash, rinse, and repeat…

When you find that you have more ‘Corners’ than vértices to wrap around them,



Just highlight the opposing vértices (Remember to keep symmetrical!) and subdivided them a few times.



Ready to keep modeling!



Looking good… But that’s a little plain. Certainly we can do a little better. Let’s add some of those kewl looking structural holes to make this a little more interesting.



Ya, that looks allot more bitchen. To add the holes on the model, In edit mode, just add circles, scale them to size, and move them into place. Remember to keep your symmetry correct.



The image file may not be 100% symmetrical. So use the Transform Properties to keep your model correct. If the Median is -1.194 on the left…



Make sure that the Median is 1.194 on the right. And when you’re finished…



Your model will be perfectly symmetrical! So we are ready to export the mesh to a DXF file using DXF exporter script listed
in the beginning of this document.



Export your model to DXF using the Autodesk que DXF (.dxf) script as pictured above. NOTE: Do NOT use the built in DXF Export. The built in DXF Export creates a valid DXF file using Polyfaces instead of Polylines. Several CAM programs do not support Polyfaces, including the current versión of SheetCAM (Which we are using here to demonstrate the process.) Use the default settings from the script.




From CAD to CAM… and Beyond!
Note: In SheetCam, you will have to define the tool, material, machine, etc, etc. which is not covered in this guide. (Perhaps later if enough people want to know but I would suggest hitting SheetCAM's forum first) Once you have SheetCam properly set up, you can import you Model and see it represented on the material it is to be cut from for the first time! In SheetCam, the Grey área represents the machines cutting área. The Red (Burgundy for you Hue aficionados) represents the Material. Blak que is the background, and your hella kewl guy part is easy to
spot! You set up the Contour job to cut out your Object, and SheetCAM generates the toolpath based on your model! Last thing to do is to run it through a Post Processor* to generate your G-Code!. * A post processor is a configuration file that defines the G-code parameters specific to your CNC Software. In my case, I am using the Mach3 post processor. (Actually called Mach2 due to the first release of Mach software)






Now it’s on to the machine!
…or, if you don’t have a CNC machine yet, but you couldn’t help reading along, there is a nifty free program out there called MicroTech CNC Simulator. (Free!!) http://www.cncsimulator.com/






CNC Simulator 3D view
(You can even see the toolpath in this
view!)


Alternatively, if you don't have a CNC Machine of your own, you can take the G-Code to a CNC Fab shop to have them create your widget for you! Please note, Most Waterjets and some Lasercutters do not use Gcode, they use the a native DXF file so you can model only to that point and then send the your DXF to cut out for you!




The cut in process!
The Yellow ‘dashed’ outline represents the material.
The Blue is the object to be cut.
The Red is the non-cutting movement of the tool.
The light green is the área that has been cut so far.
The purple gives you reference to the X and Y axis’s



You are now a Certified Blender Machinist!
Examples of machined widgets




A single rudder system for a Remote Controlled Boat


Dual rudder system for a Remote Controlled Boat


A Pan/Tilt mechanism for a tiny Camera (about 1 inch tall)


A project in the works! A Remotely controlled 3 wheeled Chhopper
This little guy is about 9.5” inches long!

www.blenderart.org