Proxxon Cnc Conversion

[Terresa Cherrie]

Thisproject will start with a standard MF70 mill and finish with a 3 Axis CNC mill with an improved Y axis travel. The costs of this project should be kept below 150 including all the endmills and other disposables.

The cost of end mills is already quite high but they should last for some time. I use a company called Sorotec for my tooling. Its all 1/8th in. shank tooling which is fine but can be a little strange as a metric person.

I intend to create a wiring diagram later in the project so that I can refine and finalise the electronics before I post to help avoid confusion. I have got a working set of electronics to run all 3 axis. This includes a relay to turn the main spindle on and off. In the final version, the spindle will not have digital speed control but its not really necessary without an automatic tool changer.

I had been experimenting with the 2 axis version for some time. I am reasonably well organised with the tools but there are loads to keep track of and several projects which use similar sets of fixings and tools. This meant that I spent some time thinking about a case for the electronics and the fixings; like the vice and the toe clamps etc.

The impetus to actually build the enclosure came when I was testing the machinability of some scrap brass when there was an almighty bang and the lights flickered and the blue smoke escaped from my workhorse atx power supply. The supply has served me well for a several years and so I am not annoyed at the life expectancy. This meant that I could not continue to use the mill until the new PSU showed up. So while I was waiting for the PSU, I used my time to make the new box.

The box was constructed from spare plywood from around the workshop and the dimensions are not really specific other than looking good and leaving enough space to mount all the cable ports and emergency stop button. there is a combination of 18mm ply, 6mm ply and 6mm hardboard. The drawer runs on the plywood base which had to be sanded very smooth to make the drawer run freely. There is a little rail used to support the shelf which the electronics are mounted upon. This shelf is removable in case I ever need to get easier access to the PSU or the control electronics.

The new 24V 15A PSU mounted on the left with the mains hard wired. As mentioned previously; the current wiring set up is not the one that will be in the final design but it works for the moment. The relay shield and the arduino nano can be seen with some basic wiring. Also I have used a 3 pin aviation connector to allow for relay control for the spindle. The connector is the same type as the 4pin ones used for the stepper motor. I could have used the 4 pin variety but this would allow the steppers to be powered with 240V AC. Not a great option. There are going to be brass plates used to mount the aviations connectors. These were the first things milled when the mill was mounted on the box.

By utilising the 2 Axis mill and purchasing some 5mm * 100mm * 1m 6068 Aluminium, I was able to start milling motor mounts, bearing holders and mounting plates for the Z axis. These were taken from one of the previously mentioned websites (All construction documents will be added when the conversion is complete).

The milled parts required for the Z Axis conversion. There are a few cosmetic issues but nothing serious. Every hole was machined with a separate milling operation which took a long time. This was to avoid any rapid moves while the Z axis is manually controlled. Many of the holes are to be tapped M4 or M6.

The parts were assembled (the bolts in this picture were replaced with shorter cap head bolts after the bearing retainer was seated. The previous coupling was made of ABS plastic but I wanted to remove the handwheels from the build. I made a brass coupling on grandads lathe. This was the only part that required a lathe in this build but there may be other ways of doing this.

The shoulder was turned to accurately fit in the bearing so as to reduce runout. On larger machines it is inadvisable to directly couple two shafts end to end. In this case the misalignment will be taken up by the flexibility in the threaded rod. The small hole is for the spring pin which holds the leadscrew.

Since I will not be needing any simultaneous 3 axis machining to build the Z axis conversion, I can make do with a 2 axes conversion. The X axis is held in place by a simple aluminium bar fixed to the T-Slot. An action shot which shows the 2 axes working together can be seen next.

The workpiece has been raised so that the entire profile can be machined without damaging the machine bed. In this picture you can see the way that both the X and the Y axes are mounted. The Z axis is done manually for the first few parts. This does reduce the abilities of the mill but it is only temporary. Great care must be taken to avoid fast travels between separate milling operations.

The plan for the mill is to temporarily convert the X and the Y axis to CNC control using 3D printed parts. Then I should be able to use the 2 axis cnc to machine the final axes conversions. I have got temporary access to a Makerbot 2X which does a great job of printing sturdy parts. I am sure that most 3D printers would be perfectly capable of printing these components.

In the shank of the coupling is a captured nut, this means that I can use a set screw to hold the coupling to the motor shaft. Since the handwheel has an M3 hole for the handle, we can use that to secure the coupling to the handwheel. The last part to be 3D printed was the Y axis morot mount. The X axis mount was fairly easy to make as the motor can be fixed to the T-slot table but the Y axis motor is fixed in place, with nothing to fix it to. This was solved by filling the gap between the motor and the table then clamping it in place. This was simple and effective but not pretty.

The first step to any conversion or upgrade project is to research if it has been done before. The MF70 is an accurate device and therefore very suitable for precision machining. The majority of the device is made of aluminium and therefore can be fairly easily worked with hand tools. I have previously built a 3D printer and so I am familiar with stepper motor control and I have access to a lathe and a small metal workshop. Since I will be upgrading the mill in several stages, I decided that a lower precision middle stage was the best way to get going on this project. By printing the interface parts I would be able to easily test and change the design without the difficulty of reworking a harder material like aluminium or brass. The bubblegum CNC project ( :33799) has some great parts that gave me alot of the initial dimensions for the build.

I think a lot more people have 3D printers than CNC mills and they're great tools. There's a bit of an overlap with a mill, but they both have their strengths and weaknesses. Comparing a mill to a printer we broadly have:

Laser cutters are expensive and I haven't seen any simple home builds. They're great for accurately cutting through soft sheet material like wood and plastics but can't do PCBs for instance. Basically they're a also a good tool, but not what I wanted.

The build quality, rigidity and accuracy of this mill is incredible for the price. There are better mills and probably some cheaper mills, but this seemed to strike an excellent balance - especially for starting out.

The only complaint I've had so far is the small Y-axis. As standard you're limited to 46mm. The X axis is OK at 134mm and the Z axis should be more than you need. It's possible to modify the mill to increase the Y axis (see my blog but that only increases it to 82mm.

I've seen a lot of builds where stepper motor mounts were home-milled. Whilst these are all good, I decided against this for a couple of reasons. Firstly, they often required the use of an existing CNC mill. Secondly, I wanted to be up and running quickly and without being hampered too much by my own inexperience. Thirdly, I'd rather get a working mill and start on simple bits of wood before tackling something tricky like a stepper motor mount (manually).

I came across a mounting kit on eBay from a seller in Turkey called *mbbilici*. It looks fairly basic and I intended it as a starting point before making my own mountings and using "proper" couplers rather than something that bolts onto the manual wheel. However, I'm still using it a few months later and have no complaints. I works really well and was zero effort on my part. Thoroughly recommended.

There are plenty of options for stepper motors and drivers, but once again I wanted a low hassle and quick solution for my conversion. The mountings I went for required a NEMA23 sized stepper and that seemed to be about right power wise. Most people use the smaller NEMA17 motors for 3D printer builds and they might be up to the job for a mill, but I wanted a bit of oomph for cutting metal.

Once again eBay to the rescue. I bought a kit of 3 motors, a 3-axis driver based on the Toshiba TB6560 stepper motor driver IC and a power supply. A search for "3 axis NEMA23" on eBay should bring up the same kit from a number of seller. I went with uni.supply. The cost for the PSU, motors and driver was 142 ($222 or 176).

I contacted the seller who agrees to let me return it, however the kit wasn't that much more than the motors on their own, so I decided to stick with it. So far it's behaved flawlessly for me. A real recommendation for uni.supply that they would take it back though. However, considering other people troubles I'm not sure I can actually recommend the board itself.

The industry standard way of controlling a CNC setup seems to be to use a PC with a parallel port and run software from ArcSoft called Mach3. There are more modern and smaller setups that are often used for 3D printers but once again I wanted to get up and running simply and quickly.

Whilst a parallel port feels like a throwback to the 90s it also means that an old PC with one should be fairly cheap - or like me you may even have one hanging around. Things I discovered whilst sorting one out were:

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