Before starting to build a machine, you will always have to make some sort of a design. Sometimes it only has to be some sketches on a piece of paper, but for this machine a more precise three dimensional drawing was required. I made my design using google sketchup. Google sketchup is a free cad program, which you can download from the web. I found it was very easy to work with, although I had never worked with a cad program before. You won’t be able to draw as complicated designs as you can, by using other programs like Autocad, but for my purposes it worked just fine.
My main goal was to get all of the proper dimensions for my parts, so that I could order them online. I wanted to see if all of my parts were going to fit together. Because the machine consists of a lot of moving parts, I wanted to make sure that nothing would hit one another while running the machine.
When I started designing the machine I already had some parts like the linear rails and the ball screws. I bought these from someone who had built a test machine for his webshop. I used the same electronics for this machine, as I used for the wooden test machine I had built earlier.
These are the basic dimensions and parts used for the machine:
Motors: Nema 23 - 3Nm
Controllers: Leadshine M542 V2.0
Spindle: Kress FME 800
Linear rails: X: Sbr 20
Y/Z: Sbr 16
Ballscrews: X/Y: 16mm 5mm pitch
Z - axis drive screw: M10 with homemade delrin nut
Aluminum profiles: 30/60mm Misumi 100mm
Aluminum plates: 15mm thick
CAD/CAM software: CamBam
Controller software: Mach3
The machine is almost entirely built from 15mm thick aluminum plate and 30x60mm aluminum extrusions. I built this CNC router using a very limited amount of tools. The main tools I used were a drill press and a lathe. Because I didn’t have the right tools to cut the aluminum plates to size, I designed the machine around standard sizes and ordered the plates online, already cut to length. The aluminum extrusions I used were also cut to length and I ordered these from misumi Europe.
When designing a CNC router it is helpful to ask yourself a couple of questions. Here you will find the design process I went through for my CNC router.
What type of CNC router do you want to build?
There basically are two types of CNC routers: the moving table design and the moving gantry design. Moving table style designs are often used for smaller size CNC routers. They are easier to construct and can be built more rigid than a moving gantry style machine. The downside of letting the table move instead of the gantry, is that the overall footprint of the machine in retrospect to it’s cutting envelope, is about twice as large as with a moving gantry design. Therefore it probably is better to make a moving gantry style machine, if your cutting envelope is larger than about 30x30 cm. Because I wanted to build a machine with a cutting envelope of about 65x65 cm, I used the moving gantry style design.
What do you want to cut with the CNC router?
This determines pretty much every answer to the questions below. I wanted to use the machine for plywood, hardwoods and plastics mainly, but also for aluminum. If you want to cut materials harder than aluminum, I recommend building a CNC mill, instead of a router.
What material will you use to construct the machine?
This is determined by the question above. A good guideline is that the material you use to construct the machine is stronger or as strong as the material you want to cut. So if you want to cut aluminum, you should use aluminum or even steel to build the machine. I have seen wooden CNC routers that can cut aluminum (you will find some on youtube), but this went very slow and the machines have to be very well constructed. Because I wanted to cut aluminum with this CNC router, I built it out of aluminum. I could have used steel, but this is more difficult to machine and I didn’t have the proper tools for that.
What length of travel do you need for each axis?
My first intention, was to build a CNC router that could handle standard size sheet goods, like plywood and mdf. In the Netherlands these are 62 x 121 cm. So for the Y - axis, I wanted a travel distance of at least 620mm. The machine is placed in a small shed in my backyard, with a very limited amount of space. I couldn’t make the machine too big, because then it would really get in the way and take up all the space. So the X - axis only has 730mm of travel. This is less than the full length of a sheet of plywood (1210mm), but I figured that if I wanted to machine something really large a could cut the first part, than slide the sheet forward and cut the last part. By using this technique you can cut pieces that are much larger than the normal X - travel distance. For the Z - axis I figured that 150mm would be enough to possibly use a fourth axis in the future.
What type of linear motion will you use for the machine?
There are many options to choose from for linear motion: drawer slides, ball bearings on V rail, V-groove bearings, unsupported round linear rail, fully supported round linear rail and profile linear rail. The linear motion system you use will to a large extent determine the cutting quality that you can achieve. I would recommend going for the best system that you can afford. After doing some research, I found that fully supported linear rails would be the best option, that I still could afford. If you search on ebay for SBR12, SBR16 or SBR20 you will find a number of different sellers and sets to choose from. If you are building a 3 axis CNC router, you should buy a kit consisting of three sets of linear rails and two linear bearings per rail. Linearmotionbearings2008 is a good ebay store from China, that sells a number of different kits, even with the ball screws included.
What kind of linear drive system will you use for each axis?
The basic options to drive each axis are: timing belts, rack and pinion and drive screws. For homemade CNC routers, drive screws are most commonly used. Screw drive systems work by placing the stationary nut on the moving part of the machine and holding the screw in place on both ends.The screw gets attached to the motor. If the motors starts to turn, the nut with the moving part of the machine attached to it, will move along the screw and set the machine in motion.
For the X and Y axis, I used ball screws. Ball screws provide very smooth motion, with virtually no backlash. Backlash is the amount of play between the drive screw and the nut and is something you don’t want in a CNC router. If you want to read more about backlash, I recommend taking a look at the website cncroutersource.com.
Ball screws are more expensive than ACME screws (which are a good alternative), but will again highly improve the cutting speed and cutting quality you can achieve.
For the Z-axis I used high quality stainless steel M10 threaded rod, with a homemade delrin nut.
What type of drive motor and controller are you going to use?
Concerning the motors, there are two basic options: servo motors and stepper motors.
Servo motors are mainly used for high end CNC routers and are very expensive. They use encoders to provide position feedback and require more expensive controllers. Stepper motors are widely used on homemade CNC routers and there are many different types and sizes. The size of the stepper motor you need depends on what you want to cut, how fast you want to cut it, what type of linear drive and motion components you use, how large the machine is etc. I used 3Nm stepper motors for my machine, which is probably overkill.
The controller must suit the motor that you’re using. You can use individual drivers for each motor, as I did, or you can buy a 3 or 4-axis driver board. You can read more about the electronics I used in step 14.
What type of spindle will you use?
Most homemade CNC routers use a standard woodworking router or trim router as the cutting spindle for their machine. Mine is no exception. I used a Kress router, which is of slightly higher quality than standard wood routers, and it has a nice 43mm clamping flange. If you want to cut a lot of different materials, some sort of speed control can be really handy. The Kress router has a built in speed control but you will find this on most routers. If you are going to be doing a lot of really heavy cutting you might want to look into air or water cooled spindles. You can find these on ebay as well, but they will cost you a lot more than a standard router. They use a VFD for speed control and can be much quieter than standard routers.
What will be the total costs for the machine and do I want to spend so much money?
I estimated the total costs for this CNC router to be around 1500 euro. A CNC router is expensive but you can save a lot of money by building one yourself.
After I had found the answers to all of the questions above, I came up with the final design for my CNC router. As you can see, my design is not extremely detailed. You won’t see the exact hole locations on all of the parts for instance. It is difficult to determine how many bolts you should use to put two pieces together, if you have never held those pieces in your hands before.
For me, this design was enough to give me a good view on how everything was going to work out and which parts I should order.
After the design was completed and rejected/redesigned a couple of times, I could start ordering all of the parts needed. The 30x60mm aluminum extrusions and all of the aluminum plates for the gantry and Z - axis which I used for the X - axis were pre-cut to length. I also ordered some heavy duty anti-vibration leveling feet.