Hi Guys
I have had a couple requests to start a build thread for my CNC machine so here goes.
So first things first, a little about CNC machines. CNC stands for Computer Numeric Control.
There are a ton of options out there for building a CNC machine of any description, the main thing you need to decide is your budget and how much do you actually want to figure out on your own.
Its possible to build a system pretty cheaply but you will have to figure it out yourself and be creative. This could be pretty fun if you are that way inclined.
A CNC machine is basically a way for a computer to control the movements of some sort of cutting device so you can accurately and repeatedly cut items out of normal sheet materials.
The cutting device on most home built CNC machines will be a traditional router but you can also mount drag knives for cutting laminates vinyl graphics or even marker pens for artwork.
Most common materials to be cut are things such as plywoods and MDF. Most modelers would be cutting stings like lite ply, balsa and sheets of foam. But it is also totally possible to cut metal as well. Its all a matter of cutter selection feed rates and cut depths. Experimenting will be required to find the optimum combination that works on for your particular machine. There are some pretty helpful and sophisticated programs that will help you calculate these settings.
A CNC machine consists of a X axis a Y axis and a Z axis, X and Y axis are normally in the horizontal plane and the Z is normally the vertical axis, where X is normally the longer of the two horizontal plane axis.
Oh and the main difference between a CNC Mill and a CNC router is that a Mill is normally a much larger substantial machine that is designed around cutting metals and the X,Y,Z axis are all much smaller and closer in size. A CNC Router is normally designed for sheet goods and has much longer X and Y axis and fairly shallow Z axis.
The machine I will be discussing here is a CNC Router.
The system I will be talking about and probably the most common for a router style CNC machine is a Gantry style. This means that a gantry that spans the Y axis and moves back and forth in the X direction and carries the Z axis and the Y axis mechanics. On the Gantry you will have a carriage that will move along the Y axis and mounted on that carriage that you will have another carriage that moves in the Z axis and that is what the actual cutting head (Router or Laser) will be attached to.
(it all becomes much more clear in the pictures)
The company i chose is called
Build Your CNC they have been around for some time and specialise in selling all the components you need to build a variety of CNC machines mainly in kit form but they also sell fully assembled machines.
They have kits for cnc gantry routers that hold something like a dremel through your average home plunge router through to the larger dedicated spindle type that i decided to go with. A spindle is a more specialised way of spinning the cutter of choice and are usually more powerful, quieter and often water cooled.
They even have a vertical version of the large machine i bought that will stand up against a wall so that it doesn't take up anywhere near as much floor space in your shop, its called the
Green Lean
I decided to go with the
Green Bull 6x as i managed to find one at a very good price. Its way bigger than i actually need but i was able save money over going with a smaller machine..
Videos on the assembly of the Greenbull can be found here


What is special about the greenbull line of CNC routers is that they are able to mount a laser tube vertically directly to the Z axis carriage. Due to the large depth of the Gantry the Z axis carriage is also very deep meaning that a laser tube can be correctly supported. Most laser cutters have the laser tube mounted horizontally somewhere at the back of the machine and use mirrors to direct the beam to where it needs to be. The nice thing about mounting the laser tube directly on the Z axis is that you no longer need any mirrors to direct the beam reducing cost and complexity. Another nice benefit is that the laser beam length never changes no matter where the Z axis is on the table.
Here is what the Laser / Spindle combo looks like.



These larger Kits are what a modeler would consider a short kit, it comes with all the special cut pieces to build the Gantry but i still have to fabricate quite a lot of the system my self. Such as the table and torsion box. The kit consists of everything you need above the support table and torsion box.
The table is fairly straight forward but its the torsion box that will need to be carefully built and as accurate as possible.
A torsion box is a pretty efficient way of getting a very stiff and flat surface to attach the Gantry to. Its basically the foundation of the machine so it has to be about as good as you can make it. Having said that, it is optional to use a torsion box you could just build it on top of the support table but if i am going to spend a small fortune on the set up then I want it to be as good as possible. It would be very difficult to add a torsion box down the road so why not do it right from the beginning.
There are lots of videos on the Build Your CNC Youtube channel that explain things way better than i can, you can
check them out hereI am lucky that i have a pretty big workshop to play in, although i do have to share it with my two girls so they have an area for arts and crafts, but i still wanted to make sure i planned out the layout as best i could and where the CNC router would best fit. So i decided to model everything in Sketchup to play about with the layout and this is what i came up with. You also have to bare in mind handling the sheets of plywood and MDF for projects. So the machine is oriented to make it as easy as possible.
I also design the support table to make sure i could store full sheets underneath it, which is easy considering the size!



Next is the final design of the actual support table.
Made entirely of 2x4's but making sure that all of the loads on the table are transferred through wood and not through a screwed joint which could be relying on the screws in shear.
All loads are directly through wood to the floor as the torsion box and gantry when finished could weigh between 5-600lbs
Thats another reason to make sure its in the right place as it wont be easy to move once its finished!!

I have actually built the table already.

Next up is the torsion box which is where the vast majority of the work of this build will be. As you can see this is the big bit!

And inside is the secret to its strength.

Since the last show i have decided to incorporate a Vacuum hold down system into the torsion box. Its easy to do now and impossible to do it later so may as well put in the extra effort during construction. Its not that hard just a whole load of holes!
I decided to break it up into 4 zones so it can be controlled more easily.
You can see the yellow walls in the drawing dividing up the cells, this is where the vacuum zones will be.
Structure detail

Thats basically where i am at right now.
This coming weekend i will be cutting all the material needed to build the torsion box. Hopefully i can also start the assembly process but that will probably be the following weekend.
Will keep you posted
Cheers
Ben