For years as a hobbyist that buys all kinds of add-ons and accessories for "mu millions of Hobbies" according to my wife. I have thought how amazing it would be to have my own CNC mill and lathe equipment to make a lot of these items myself. It would also be really nice to have the ability to personalize them with my own logo and name or whatever catches my fancy. So I went out and started pricing small milling machines and compact metal lathes, and even combo mills with a built in lathe. It was then that I realized if I dropped the kind of dough needed to purchase this equipment, that I wouldn't be able to afford my hobbies anymore. So I set out on a quest to build my own CNC mill.
Do you just jump into milling?
Now I have some experience in milling and machining. I worked in a factory in the maintenance department and we were able to use a lot of their tool makers shop to do repairs on machinery and create and repair tooling. So I got a really good taste of hand milling and turning everything from a 10" dodge bearing from scratch to trueing dinged ball screws, to facing 2 ton shaper heads.. All this on old manual knee mills and old Colchester lathes. At the same time I was on a team that converted old relay logic machinery to PLC controlled and CNC operated machinery. This really gets you involved in how the machines operate as well as how to visualize the build process.
Well, there are a couple of reasons. The first is the Chinese market influx of affordable CNC controllers and stepper motor drivers. There is also a larger availability of scroungable steppers motors and accessories from old copiers, printers and plotters that can be used to build your mill affordably. I guess it is also something you need to take your time on and all we seem to have as we get older is time right? Just Kidding.
I soon found out that a couple of motors that I thought I could use to build my mill, were both too small and to weak to do the job. So in my visits with a guy I know in the service industry, that was parting out and old Ricoh copier, he acquired me four NEMA 17 1.8deg 1.2A 6 wire stepper motors. To run these from the Arduino as I had hoped would require at least 2 motor shields, and even then they were not rated for continuous duty nor the current like I would need. They also run upwards of $30 each. So I started the process of looking for a cheaper and or better alternative. More on the controller I decided on later.
|Old Gantry design|
So I set out to make a base from the HDP and some extruded scrap aluminum I had laying around. I don't have a lot of photos of this process, but will post what I have. I basically just wrapped the edged of the base sheet with the extruded aluminum on the long edges and then used two pieces of 3/4" angle Iron mounted across the end. I later applied a 1/2" strip of the HDP across both ends and extended them out long enough to mount the gantry rails on. I should let you know that with the HDP, most of the assembly is done with sheet metal screws. I predrill all holes, otherwise the material distorts or cracks.
|First design of gantry rollers|
One thing you learn very fast, is even though you do your research
New rail design.
X-Axis lead screw.
|Ball Lead screws|
Most CNC mills have high precision ball screws that move the axis' back and forth. They have built in back lash nuts that reduce play to almost nothing. The problem with these are they are extremely expensive, and for my purposes not needed.... yet. With a little work you can get a home made lead screw to hold pretty tight tolerances. I created my own lead screws from 3/8 Ready Rod and 1/4" ready rod. Though I am planning on making them all 3/8 before I am done, as the 1/4" screw seems to work the motors harder. It is also much easier to synchronize screws that are all the same size. I have also heard that some software that will not do certain operations correctly if the X an Y axis do not have the same pitch. Mach3 has no trouble with this at all though.
I made some homemade dodge bearings for each end of the screws by grinding down the
|DIY Dodge Bearing|
|Finished X Axis Screw|
|Nut for screw drive|
I made the nut to drive the axis out of a small piece of the HDP, by drilling and threading a hole for the threaded rod to screw through. One tip for this is that no matter what material you use for the screw nut, take a drill and clamp the end of your screw in the chuck and then power the screw back and forth in the nut a couple dozen times at high speed, over the entire length of the screw, to seat in both the nut and the screw to each other. This makes for much smoother operation and less drag against the motor right out of the box. When completed the X axis with the 3/8" ready rod had only .003" of backlash, that I easily took out in Mach3's backlash compensation. I will be building an anti-backlash compensator nut at some point, but I am pretty happy with what I achieved with this homemade screw.
Normally you would use a dampening motor coupler in this situation, but finances dictated that I make something instead. I needed a way to get the motors connected up to the screw. Since I was going the direct drive route instead of belt or gear this is pretty straight forward. So I took a piece of scrap aluminum stock that I had cut off the end of the rails that had been installed, and drilled holes in the ends to match the 5mm motor shaft. I then ground the threads off the end of the screw and drilled the correct size hole to fit it in the coupler. I also drilled and tapped a 3/16" hole for a set screw in each end to lock the shafts into the coupler. I will be changing this later to a flexible couple, mainly to save on bearing wear and tear for the motor. It should also help on harmonics noise to some extent.
|X Axis Motor Mounted|
Once I finished mounting the motors I started on the build of the gantry. I knew I wanted at least 3-4 inches of travel in my Z axis. I would like more but did not feel I would be able to control tolerances with a much taller gantry. I used a 3" strip of HDP up the sides and quickly realized that this stuff flexes a LOT in longer lengths. So I had to reinforce all of it by screwing aluminum flat plate to the edges. This helped to support it from side to side deflection that might occur. The horizontal piece wasn't as big of a concern, as it was going to get more support later.
So there you have the first part of my DIY CNC build. In part 2 I will go into the building of the Y and Z axis Carriages and the building of a controller that will work well and be expandable too. Here is a little sample of what's to come.
|Z Axis Carriage|