This article will walk you though all the steps in planning, choosing the parts, building and using your DIY CNC.
Computer aided design, or CAD, has always interested me but up until recently I haven’t needed to manufacture parts requiring CAD, , and finding out how much companies charge to mill parts, I decided I would make my own machine to do the job.
My main goals were to be able to cut plastic, wood, and soft aluminum keeping the cost under $750 USD.
To date I have spent around $1041 on the build out of the CNC.
The first step in the DIY CNC is to decide on what plans you are going to use for the build. Will you have a fixed gantry or moving gantry? Are you going to make it out of wood, plastic or metal? What controller board and steppers are you going to chose?
Here is a list of exactly what I ordered for my build:
- 1 Hobby CNC Controller, Steppers kit HCNCPROPKG Hobbycnc.com
- 3 Flexible Spider Shaft Coupling Hub, 1/4″ Bore, 1-23/64″ Od 6408K121 McMaster.com
- 3 Flexible Spider Shaft Coupling Hub, 1/2″ Bore, 1-23/64″ Od 6408K712 McMaster.com
- 3 Buna-N Spider For 1-23/64″ Outside Diameter, Flexible Spider Shaft Coupling Hub 6408K73 McMaster.com
- 12 Black-Oxide Steel Set Screw Shaft Collar, 1/2″ Bore, 1″ Outside Diameter, 7/16″ Width 9414T11 McMaster.com
- 6 Steel Ball BEARING–ABEC-1, Dbl Sealed, No. R8 For 1/2″ Shaft Dia, 1-1/8″ Od 60355
- 3 1/2″-10 Acme Size, 10 Tpi, Standard Nut For, Precision Modified-Acme Threaded Rod 6350K41 McMaster.com
- 2 1018 Carbon Steel Precision Acme Threaded Rod, 1/2″-10 Acme Size, 10 Turns/Inch, 6’L, Rh Thread 99030A105 McMaster.com
- 3 12L14 Carbon Steel Tight-Tolerance Rod, 3/4″ Diameter, 6′ Length 5227T28 McMaster.com
- 12 Sae 841 Bronze Sleeve Bearing, For 3/4″ Shaft Diameter, 7/8″ Od, 1-1/2″ Length 6391K207 McMaster.com
- 1 ¾” MDF 4′ x 8 ‘ Sheet Home Depot
- 1 Project box for controller Radio Shack
- 1 Transformer 115 VAC to 24 VAC 10A F-401U alliedelec.com
- 1 Rockliff CNC router plans rockcliffmachine.com
One thing that I did for this build is to order everything at the same time so I am not held back by delayed shipping or other problems that could delay the building process.
Here is a photo showing all the parts needed to get started, the only thing not shown is the threaded rods.
The first thing assembled was the stepper motor driver kit. It comes in a bag with what at first glance looks a little scary with all the components just scattered in the bag, but after opening it up you discover that HobbyCNC has written a wonderful manual explaining each and every step in building the driver kit.
There are a few parts that need to be soldered in place to achieve the right orientation, otherwise they wont work. I made that mistake once and had to de-solder the part and flip it around! You want to follow the manual exactly how its written as there are a few tests that you need to perform before you install the last 3 chips.
Here is my 3 Axis driver kit fully assembled.
I reviewed a number of the many CNC router plans. I needed to take into consideration difficulty of building, cost, time to build it, and what materials it used.
For this build I went with the Rockcliff CNC router plan. It features and fixed gantry 5″ for the z axis and 18″ x 18″ for the x and y axis. There design is fairly simple and easy to understand. I built mine out of MDF. I took the plans to Kinko’s and got them printed at full scale 1″ = 1″, and then glued the plans to the sheets of MDF using aerosol spray can glue.
At first I tried using a jig saw to cut the pieces, but because it’s an inexpensive saw, I was not able to get the cuts to be perfectly vertical. I then broke out all the tools I had in storage; a table saw, power miter saw and circular saw.
Now that I was using the correct tools the process started to go faster and cuts where looking 100 times better then before. Then I started working on the gantry sides. At this juncture all my good luck went bad. After cutting both sides out and putting them next to each other they where not even close to being exactly the same size and shape. If these two sides aren’t perfect the whole machine will not work right.
After a few hours of trying to figure out how to make both the sides the same I had the idea to screw them together and then make all the cuts and holes needed; this worked out very nicely. I then had two identical sides.
I based a few modification from Don’s router (cnczone.com), The Y Axis is bolted down to the table and not part of it, and the gantry support brace is made double thick to add more strength to the machine.
The machine is designed to have the gantry easily removable from the main table by removing the four Allen head bolts from the gantry sides. This allows for servicing and for transportation as the full machine weighs close to 100 LBS.
After the basic machine is built you can start to get a idea of what the machine is going to look like and the scale of it. My machine is about 20″H x 40″L x 25″W and is built using almost a full 4′ x 8′ sheet of ¾” MDF.
The next step is to choose an axis to begin construction. I started with the X axis. First you want to cut the steel rod about one inch wider then the gantry. I then slid 2 bronze bearings onto each rod. Its always a good idea to do a test fit of the parts before you glue everything together, so I clamped the X Z plate to the bearings and slid it back and forth. There was some binding toward each side of the gantry so I took the bottom rod out and sanded the holes in the gantry. This minor adjustment made the X axis slide like butter both ways. Now that the axis moved smoothly, I glued the bearings to the X Z plate using Gorilla Glue, then clamped all 4 sides and let it dry for a few hours.
I repeated this step for the remaining two axis.
The design calls for ¼” – 20 threaded rod for the drive shafts (the 20 after the size means how many Threads Per Inch TPI there is). To try to save money I went with the ¼” – 20 rod, but after installing it I found that it was not strait enough and would whip around on the unsupported ends, and eventually ripped the y axis mount out during trials.
So I then decided I will go with ½” – 10 precision threaded rod, with real motor couplings and bearings for support on each end (this is what caused me to go so much over budget)!
The reason that the Acme precision threaded rod is so good and possibly why so expensive, is that on most standard threads the shape comes to a point. On the Acme, each thread is more squared off. You can see a close up of the acme in the thread tap photo. Because of the square threads it makes a very smooth and precise drive system.
After looking for a good way to mount a nut to each axis, I found one that would work that had a flange and 3 holes in it. What I did not realize is it was made for the precision modified thread, so it just would not go on easily.
I cut the nuts to about one half the original length, as shown.
Since I really did not want to have to wait another few days to get a thread tap or new nuts I used some spare Acme rod and used the jigsaw to cut four notches down about 3 inches long. I then sanded it into a point using the belt sander. This worked beautifully as it rethreaded the nuts and they now all spin very freely on the rods.
So now that the nuts are on the rod I had to fabricate new motor mounts since the Love Joy motor couplings where a lot larger then the previous couplings. I was able to do this my making standoffs that are 1.5″ long. This made room for the new coupling’s but saved me the trouble of having to make all new motor mounts from scratch.
It took a little bit of modification to the motor mounts since the new couplings where about 1.5″ long and pretty wide; you can also see how big the drive rods are compared to the ¾” slides. Again I started with the X axis then moved to the Y axis and finally the Z axis shown below.
One thing that should be noted is that the nuts attached to the wood are temporary; once the machine is fully functional I planned on cutting some brackets that will allow all three screws to be used making a much more sold mount.
So now that you have the basic machine built, it is time to wire everything up to the controller. In my case the stepper motors are 305oz and have 8 wires, the controller board only had 6 wire outputs. This is because 4 of the wires are common/GND. Since each stepper has different wiring you want to be careful in wiring the steppers up so they will run correctly.
To power the Steppers, I originally used two computer daisy-chained power supplies, but after a while of having them both wasting desk space, I ordered a 115 VAC to 24 VAC transformer. This has to be connected to a resistor bridge that converts the electricity to DC and then stores the power in the large capacitor until the power is needed.
Now that all the wiring is done its time to decide what software you want to use,
There are a number of good CNC interpreter programs that are available for $50 – 300 for a license.
I will be talking about the Mach3 program, it runs on a windows computer and will run up to 1000 lines of G-Code in the trial version.
When you first start Mach3 you first need to go in and set the pins for each stepper motor so that Mach3 can send the signal to each stepper so that it will turn in the correct direction. The next step is to configure the Turns Per Inch (TPI) the stepper motors turns at 1.8 degrees per step, so 360/1.8 = 200 steps per full turn.
So now that we know that to make the stepper turn one full revolution it needs 200 steps, and so to move the nut on the Acme rod it takes 10 revolutions. With some simple math, we get 200 * 10 = 2000. But with the HobbyCNC board there is a thing called “Micro Stepping”. I have set mine to ½ so to move the nut one inch I would have to set Mach3 to 4000 steps per inch. The micro stepping can help make the machine more accurate if used correctly.
On the same page that you configure the steps per inch there is a setting called “acceleration”. Now this is a setting that is very important! If the number is set to high the stepper will just stall randomly. I have set mine to 30 IPM on all 3 Axis to get the steppers to work without constantly stalling.
So now that you have the software configured its time to turn the power on to the machine. If everything goes well you should hear a hissing noise from all the steppers this is a normal sound; they also will get extremely hot after being on for a period of time. This is completely normal.
The first thing I did was set the IPM to a very low number like one, and then try to Jog the machine. The arrow keys will control the X and Y axis and the page up/down keys will control the Z axis. So press an arrow key and see if anything moves. If it does, you have configured the software correctly and wired everything up the way it should be.
What I did next was slowly increase the IPM until the machine would stall out; I then lowered the number by 5-10 and set that as a base line for testing the machine.
This seemed to work well and I did not have any stalling problems. Now its time to try to cut something!
I use Alibre Design Xpress to design my CAD. It’s a free program that is very simple and powerful; once you have the design you want to cut you can export it as a STL file or a 2D DXF file.
If you are using a STL file you need to use a program to convert it to G-Code. I have found ACE converter works perfect for this. So now that you have the G-Code you can take that to the computer that is connected to the CNC and open Mach3, go to file > load G-Code. Then move the machine using the jog controls to the point you want as the start, zero the machine and then hit the start button.
If you set the machine up correctly and the software is configured correctly, you should see it cutting the design out. It took me a few days to tweak the machine to the point where I would be comfortable to walk a few feet from the Emergency stop button.
After it was all built and running it was so rewarding to see the motors moving and to hear the wonderful sound of the steppers. And to now be able to manufacture prototypes for my products is just awesome!
Would I do it again? Definately (even though it came out over budget by a few hundred dollars). In the end, the upgraded Acme rod is what ended up making or breaking the system. It was also a great learning experience to discover what power tools work for what and what don’t.
I look forward to cutting designs and products for a long time to come on this home-built machine.