CNC milling machine project

Hi, 

Recently I got interested in diy cnc mills. We have a mill at my university, but usually I have to wait a few days for the operator to become available, as he has a lot of work to do. So basically this slows everything down. As I design only small parts for the brushless controllers I decded to make a small "desktop" cnc mill. The only assumptions I made at the beginning were: low overall cost and ability to mill in aluminium. 

With that being said I started to search for different designs of cnc mills in order to pick one as a reference. I stumbled upon many 3d printed mills (which I automatically rejected due to the limited stiffnes of the parts and overall durability) and very professional cnc mills that cost a fortune. I wanted something  in between. That's why I contacted my friend from electrical engineering departament, who had already built one in the past. His design was rather simple but at the same time it ws very stiff. It was a combination of aluminium 40x40 profiles and mostly 15mm thick aluminum plates. I decided to make a silmilar machine, with a bit larger working area. 

While planning I came across an auction where I could buy a used 2.2 kw hy02d223 VFD for like 50$. I contacted the guy and eventually I bought a spindle mount, VFD and supported shafts for the z axis (is that the proffesional term?) with bearings for about 80$. That was the starting point. 

Fig. 1 Z-axis, 80mm spindle mount, and the VFD

Since then I made a few attempts to prepare a 3d model of the mill. After many different approaches and ideas I eventually decided to make a structure similar to my friend's mill. It consists of a lower frame (y axis) made of aluminium plates and profiles between them. The upper part is mounted on two 15mm thick pieces of aluminium plates. Two profiles perpendicular to the plate make the x axis. X and Y axis are equipped with linear rails (Chinese hywin), and the Z axis moves on supported shafts which I bought. 

Fig. 2 3d model of the milling machine

X and Y axis are driven with 1605 ball screws, whereas the Z axis is equipped with 1204 ball screw. I plan to place a 65N furniture gas spring (the one mounted in the furniture fronts, to make it easy to lift), so the screw will not be loaded a much. 

I started the construction from buying the 2.2kW water-colled spindle, dm542 motor drives,  nema 23 3Nm motors, motor power supply, ball screws with bearing blocks and linear rails, a PC and LPT port control PCB. Aluminium profiles and plates come from a company that disassembles machines and other pieces of equipment and sells the parts. They were much cheaper than new profiles and aluminum sheets, so I decided to purchase them. There was a few additional things as cables, screws, induction sensors, lightning etc. Right now the overall cost is 4000PLN (currently about 1000$). I do not think it will change much, as I have the majority of the parts needed. 

The assembly started from milling the 15mm aluminium plates and cutting the profiles to 670mm. After cutting the profiles with a saw, they were milled in order to have the exact same length and perpendicular surface. 

Fig. 3 Lower frame after milling

Having done some online research I found that people use to fill the profiles with epoxy and sand, concrete, or some different filling. It is supposed to make it heavier and damp the vibrations to some extent. The epoxy option was quite expensive so I decided to fill the profiles with special concrete for leveling the floors. The producer claims it has low linear contraction and easily fils the empty spaces. With a little help from my university club's colleges we managed to fill the frame. We put some water in the holes and slowly poured the concrete while shaking the whole frame. If was quite a mess, but eventually the frame was filled. I struggled with air bubbles pushing the concrete from the holes for some time, but breaking them with a piece of wire seemed to help. 

Fig.4 Concrete filled frame

The only thing that I realized after filling the profiles with fluid concrete is that I could fill them with loose concrete and tamp it inside so that it stays solid. Maybe this way I could manage to put more concrete in the same volume, and the damping properties might be enhanced. I will try it with the  profiles for the x axis.

That is all for now, 

see you ;)