I was talking to a fellow member of my school's robotics team, and we got to thinking that we should build ourselves a CNC mill to machine custom parts with. While doing some research, I came across and Instructable called "How to make a mini milling machine- manual or CNC!." The design of this particular machine is very good for a small scale milling machine, and I got to thinking I could scale it down even farther- much farther. This project is the result.
This project is entered in a few contests on Instructables.com. You can vote for me in the first contest here, in the top left corner:
It really does not take much in the way of materials to build this. Here are the tools and materials I used.
Square dowels- lots of them, a few different sizes helps
1/8" plywood. Mine is marine mahogany, because I have some scraps of it.
Furniture nails- use anything thicker and the wood will split almost every time
Drill with lots of small bits
Stainless steel axles- these can be taken from RC cars
3 long bolts and twice as many nuts
Dremel tool with flexible shaft attachment.
Box cutter- for cutting the brass tubing
Wood carving knife
"U" screws with bolts
In this mill design, the base of the mill contains the Y axis. To approximately match the length of the axles, I made the base 3.25" square. To make the rails for the platform to slide on, I drilled 4 holes through opposite sides so that the axles fit parallel to each other at the same height. All the joints are both nailed and glued in place.
The next platform up contains the X axis. It is constructed similarly to the base, but with dimensions of 1.25" by 2.75", and the rails are raised up. On the base of this level, two sockets are fixed that slide on the rails of the base. The sockets are short segments of dowel which have been drilled out and have a piece of brass tubing in them.
The sliding bits are made up of these two pieces:
The two platforms attached to each other:
The next step is to build the milling platform. The platform is the part of the mill that whatever you are milling is fixed to. I estimated the range of motion of the mill, and cut a platform to the corresponding size out of mahogany plywood. Onto the bottom, I fixed sockets that slide on the rails of the second platform.
The next step is to build the tower to hold the motorized part of the mill (in this case a Dremel flex shaft) and contains the Z axis. This was once again built with square wooden dowels. Unfortunately, I ran out of stainless steel axles, so I used some thiner brass tubing instead. It is very important that the tower extends the right amount outwards, or the milling bit will not be able to cover all of the platform. With this design, the bit has to be a little in front of the center of the base.
The original design:
The next step is to build the part of the tower that will actually move up and down, and will hold the dremel. The base of this part is made up of more plywood. I added two segments of dowel down the middle and carved their corners out to fit the contours of the dremel attachment. On the back of the piece, I fitted two more sockets to slide on the rails of the tower.
In order to make the platform and milling bit actually move, I had to add lots of threads. In the base of each moving part, between the two rails, I fixed a set of nuts that a long bolt fits through. If the bolt is held in place and turned, the platform moves forward or backward depending on the direction you turn the screw. The end of each bolt was fixed with a locknut and a piece of wood to stop it from moving. It is critical that the nuts are lined up perfectly perpendicular to the rails, or when the bolt passes through them it will not be parallel, which will cause problems when the platform moves.
I mounted the Dremel attachment to the mill using "U" shaped bolts and some perforated aluminum. In order to not block the rails, the lower U bolt was bent at a 90 degree angle, and the threads protrude forwards instead of backwards like the first. I bent a piece of perforated aluminum to fit around the Dremel and hold it in place when bolted down.
Mills tend to work better when they are fully assembled, so I had to find a way to sturdily fix the tower to the base of the mill. I started out by simply nailing and gluing it to the base, but this proved to be fairly flimsy, so I built a larger base and triangular supports for the tower.
To actually use the mill, will need to mount whatever you are milling to the milling platform. I accomplished this with very small wood screws. Obviously, this will not work with any material more substantial with wood, but past that point the entire mill would probably break, so it is not really an issue. It is helpful to hang your dremel up above the mill while using it, so that the weight of the flex shaft does not tip the mill over. I have a loft bed, which makes hanging it above my desk very easy.
Test piece screwed into the milling platform: