Homemade CNC2 (Electronics - Part 2)

This blog is actually about a small disaster I have with my home made CNC. And I named it "Electronics - Part 2" because I believed that the problem seems to be with the electronics.

So I have GRBL controller on the CNC and everything works fine. The next thing I would do is to machine the end piece again for my Y-axis extension. This time I planned to machine it in aluminum. So I got some 5/16" aluminum, and go really slow with it (0.2mm per pass). It took a long time and I was watching the process, and got really bored. So I closed the enclosure and went on to do something else. When I got back to it after a while, I heard that something is wrong. I rushed in, and went for my panic button.

It was bad. The machine goes to some completely weird path. The end mill bits are broken. Not only the work piece is ruined, it gouged a deep mark onto my compound table. In additional, all the alignment of the machine is all thrown off.

I have been thinking about what went wrong. Eventually I came to a conclusion that this might be an isolation problem with the electronics. The step stick stepper motor driver I am using have both the logic and the driving power supply connected. The noise from the driving power side might get into the processer side and messed with the serial commands. That's just a guess based on logic deduction, and I have no prove for it. That give me an immediate next step work item, that is to build an isolation stage into my controlling electronics.

This really highlights another important aspect of working with machines and tools - the safety is a very important issue that can not be stressed enough. It was fortunate that I have an enclosure for the CNC, so whatever went wrong stays inside the cage. It is also a great practice to have a panic button that can stop all the machine operations right away. Because when you are at that moment, there is not much logic deduction going on. A pre-defined single safety action (such as pushing one button) would be a great feature to have for any machine.

For now, I will stay with machining plastic materials and stay watching it all the time during the process.

Homemade CNC2 (Enclosure)

I have been playing with my new CNC, and have machined some pieces for the Y-axis extension modification. While I am machining the pieces in ABS (which is harder and more brittle compared to HDPE), I noticed that the dust from cutting is getting in the air and making me coughing. Since part of my use of the CNC will be to do circuit board routing, it may produce some other harmful dusts as well (circuit boards are made of fiber glasses, which is really nasty if inhaled). So I decided that it is time to make an enclosure for the CNC to contain the dust from cutting inside. In additional, an enclosure will be very helpful for the safety in case some thing goes wrong or some pieces flying around. (This proved to be very useful in an event happened lately).

So with some quick scratch and using the scrap wood I have laying around in my garage, I spent a couple of days to put together a quick enclosure. In order to leave me with un-obstructed access to my working area, I used a cantilever design so the front of the enclosure is without any supporting column. I am not going to put my weight on the shelves besides my controlling electronics, so this should work pretty well. The only problem with that is from the think Plexiglas sheet I have bought. Since the sheets are the most expensive piece of the enclosure, I went for the thinnest I can get. It still cost me almost $30, but the sheet is so thin that it warps. Without the front columns for it to be fixed on, it leaves some gaps between the front and side shields. Oh well, as we know, a perfect solution is a luxury that a home shop does not have. And that is part of where the fun comes from. I used some tape to keep the pieces straight and together.

So here is my CNC enclosure in place. It is not too bad considering how much it costs me.

Homemade CNC2 (Y Extension - Part 1)

Now I got the CNC working and made some test cuts on wood, plastic, and aluminum. Everything works beautifully. It is tight and precise after calibration. And what I like most about the traditional compound table and fixed head design is that I can change the tool bits between different cuts without losing the X/Y coordinates. This was not possible with my previous ShapeOko build.

While I am continuing back to build things useful, I quickly run into a limitation of this CNC. The Y travel of the compound table is only 43 mm (a bout 1-3/4 inches). That limits the parts machined to a very small size. I have mentioned in my previous blogs that there are a couple of ways to extend the Y range (such as Retromaster and 0xFRED). Personally, I think the method by Fred is a much better solution.

First, I went out and bought some small ball bearings from eBay for a few bucks (thanks to China). The bearing is of the size 6mm ID x 12mm OD x 6mm thick. It is small and fits well into the limited space there. The stock Y axis threaded rod is just a bit short, so I also got M6 threaded rod from McMaster-Carr (a great place to source parts, material, and tools). Note that by convention, the Y axis rod is always left handed, although it does not matter if you don't plan to hand crank it. I may replace it later, but for now the center driving nut is left handed, so to make things simpler, I got a left handed rod.

Since I have a lathe, I decided to turn down the end of the rod. I have also turned a small collar to go on the rod. Since I don't like the holding pin Proxxon originally used, I decided to use a die to thread the end that I have just turned down, and to hold the collar in place with a small nut. This has proven to be a bad idea (which I plan to fix later with a different design). As one can see from the picture here. The rod is made with soft steel, which is very difficult to machine. So the thread I made on it looks terrible. Further more, I found that the holding nut will get loosen after some time. But for now, that has to be it. I will have to make it work so I can use it. Proper solution sometimes is a luxury a home shop could not have.

So after measuring the sizes, I got the CNC to cut a part for itself. (A machine that can be used to build itself - sounds like a neat line) Anyway, I made the pieces with some 1/8 inch ABS plastic I have laying around. ABS is just strong enough for a temporary piece, and if my measurement is off I can make things fit with a utility knife (as shown in the picture above).

In another picture, the moving part of the compound table is sliding beyond the end plate of the Y axis. After everything is assembled together, I got to measure the travel of my new Y axis. It is now a whooping 100mm (just under 4 inches). Now I can finally cut pieces that are wider than 2 inches.

Here is how the new extended Y axis look like now. I will come back to fix the rod with a better design and remake the end plate in aluminum. But for now, it works.

Homemade CNC2 (Y axis)

After finishing the X axis, I started to get on the Y axis. After all, what can I do when I have a one axis CNC?

The pieces for the Y axis is very similar to the X axis. Here is a picture of the original parts. The Y axis of the HF70 milling machine tables has notoriously short travel. People are coming up with various ideas to extend the travel of the Y axis (such as Retromaster and this one). I plan to do one of these at a later time, but for now, I need to push forward to finish the conversion so I can have a working machine.

So the conversion is very similar to what is done on the X axis. Same cylinder shaped piece is replacing the handle. The plastic piece is removed leaving the steel piece in place. When it is done, it looks like this in the picture below.

Next comes the stepper motor. This is much easier than the X axis, as the Y axis is sitting on the base. All I need to do here is to mount the motor somewhere with the right height.

So out come my saw and a measured cut on a wood piece. Here it is, the stepper motor is sitting on its place, connected to the end of the rod with a rotation coupler.

Here is now the completed Y axis look like. Next comes a lot of fun time calibrating the system and making test cuts. I have some left over electronics from my last 3D printer build. So it is easy and quick to get the stepper motors hooked up. And here I have a completed homemade CNC from cheap parts I can get.

Homemade CNC2 (X axis)

After a long break from this project, I am back to continue working on it. Now it is time to convert the compound sliding table to be controlled by stepper motors.

For the compound table, I used one that is the same as used as MF70. I got it for $90 on Amazon (see my previous post). There are a few articles on Internet that discussed the conversion of MF70 milling machine to CNC. They gave me inspiration and ideas.

• http://www.thebox.myzen.co.uk/Hardware/CNC_Conversion.html
• http://retromaster.wordpress.com/mf70-cnc/
• http://www.jarkman.co.uk/catalog/cnc/mf70.htm

The first axis I worked on is the X axis. The disassembly is simple. The only place that is a little tricky is to remove the pin that holds the handle to the end of the threaded rod. I used a small drill bit to punched it out.

The parts looked simple enough. Basically, I just need to make a stepper motor mount and extend it so it is attached to the end of the sliding table. At the end of the sliding table, there originally is a steel piece hold inside a (black) plastic piece. The threaded rod is turned down at the end, and fitted with a sleeve bushing which rides on the steel piece. I decided that the plastic piece is not needed, as long as I keep the steel piece in place. I may want to convert that into a ball bearing later but for now that is good enough.


I have made a small piece on my newly acquired Craftsman 109 lathe. Even though it is a beaten up old lathe from half a century ago, I found that lathe and milling machine are tremendously helpful and complementing each other when making parts. The piece I made was the small cylinder shaped piece at the lower right corner of the picture. It is drilled so the pin can hold it to the end of the rod just like it was for the handle. The coupler then connects the stepper motor to the rod.

Here is a picture when the pieces are put together and assembled on the sliding table. The rotation coupler is not installed. The cylinder piece is pined to the rod, with the sleeve and a washer act as the bearing surface between the rod and the steel piece when the axis is rotated by the stepper motor.

I used this chance to check for alignment and makes sure everything is in place. As one can see, the stepper motor is not perfectly aligned so I spent some time to get that straightened up.

Another thing I do differently here is that I used a two piece aluminum angles to make a U-channel shaped extender. I saw people on the Internet who used U-channels there. I was about to do that originally. But after some thought, I figured that this two piece is a lot easier to assemble onto the sliding table, as you can see the screws holding the steel piece (which holds the extender onto the table) is a bit hard to install if this was a U-channel. On top of that, I don't have a U-channel at hand, but do have these angles.

So finally, here is my X axis, converted to CNC.

Homemade CNC2 (Frame)

After the Z head is ready, I needed to make a frame to hold everything together. Since wood is the easiest material to work with, I put together a quick frame.

It is nothing fancy, just for everything to be put together. And with the Z head and X-Y compound sliding table mounted, the CNC is taking shape.

I did need to put some wood blocks underneath the compound table to get it to the right height. With a little controller I have left previously, I was able to move the Z axial up and down. It is quite a bit tight as one would expect from the imprecise wood construction. But we can improve on that later.

Here is how it is like after a first test cut on a plastic block. I have then used it in the rebuilding of the little Craftsman 109 Lathe.

Homemade CNC2 (Z Head)

The first thing I built for the CNC is the Z head. As a starting point , I went to Ebay and got a cheap linear slider for $20. It is the black metal slider you see in the picture below. It is made by DI, and has a travel range of a bit over 2 inches (which is sufficient for a CNC). I also plan to use the tool holder I have left from my ShapeOko after I have converted it into a 3D printer.

I have been thinking about different materials for the base board. Aluminum is definitely an options. But after some consideration, I decided to use wood. It is very easy to cut and shape, and has great strength weight ratio. It is cheap and easy to acquire too. The only downside of it is that the bulk of the size needed to reach the strength needed. But that is an acceptable trade-off for this build, as I can always replace them later. So here is the top plate of my Z head, with holes drilled for mounting.

These are assembled together as below, with a 300W spindle (which I also got from Ebay) mounted on the tool holder.

Next, we need put together the linear drive. For the Z-axis, I used a simple threaded rod going through a HWPE block. The HWPE block is a low friction plastic and is used here to achieve low backlash linear drive. It is a very simple setup. The threaded rod is hold with flanged bushing that fits into the wood blocks. The bushing is made of bronze with built-in lubrication. Two nylon insert lock nuts are used on each end as the holding points (which rides on the flange of the bushing). The stepper motor mount is made with an angle aluminum with a few drilled holes. Again, the coupler is purchased from Ebay.

Here is how everything are put together. A few more nuts are added for mounting the Z-Head plate to the Z post.

Homemade CNC2 (Planning)

Since I built my first CNC with ShapeOko (see my previous post) as a learning practice project, I have being thinking about designing one by myself and build it. I have since converted the ShapeOko into a 3D printer and gave it away in a hurry. So for the new build, I will have to start from scratch and bootstrap it again. This is challenging because as we know it usually takes a CNC to build a CNC.

One thing I am thinking differently now is that I may want to build a CNC just as a CNC, instead of a potential CNC / 3D Printer combo. I have looked at a few milling machines and their CNC conversion. Also from my experience playing with my last build, I realize that it maybe advantageous to have a CNC with fixed tool head (and Z axial) with a separate X/Y compound table (as in traditional CNC). One advantage of this configuration is that enables easy change of tools without disturbing X and Y position. It also makes more sturdy and stable machines too, which is more important for CNC machines.

I have looked at the Harbor Freight milling machine (at $600). Another one of interest is Proxxon milling machine MF70 (at $400). But both of them are a little expensive. Then I found that the compound table of the Proxxon machine can be had for $90. That is perfect.

My plan is to build the head and the frame from there, and then put it with the compound table. Afterward, I can use it as a mini milling machine to mill the parts that is need for CNC conversion and go from there.