Design and build of a metal structure 3 axis CNC router.
Hello everybody!
This is one of my first posts on the site, and its gonna be a follow up about my (already started) construction of a CNC machine.
After I became aware of the existence of such machinery, the desire of building one of my own became real, specially being a construction and implementation of ideas freak since very young, building such a machine became a reasonable next step, as for the ease and speed up of creation of parts for different purposes, be it art or parts for other machinery, etc.
Some 3 years ago I decided to build a small machine with whatever parts I could find that I already had, like reusing printer and scanners steppers and linear rails with bushings and drawer slides. So i built a small machine having a work space of approximately 11x11x2cm, running on 3 unipolar steppers, geared to standard 5/16 threaded rods and DIY antibacklash nuts, cutting with a Dremel. The machine works pretty well and I had put it to use for some many hours engraving and cutting all sorts of stuff on wood, but the precision is not great as this was a merely educational attempt to attain the concepts of CNC and I didnt put a lot of attention into making it rigid, and put more attention to build it as fast as i can to have a working piece in little time, using wood as the structure of the mill.
So why stop there, I thought, and I started to design the next machine I would build, in my head at least..
Now I knew that I wanted it to be as rigid as I could possibly make it with the resources and tools that I have. I also want it to be fast (ballscrew driven in some moment, but I'll start with standard threaded rod), precise, made with easily and cheaply available parts, definitely bigger than my last mini CNC, and capable of milling aluminum and other soft metals, using a much more powerful router than a Dremel.
A while ago I bought online 3, 570 oz/in nema 23 stepper motors, so now I wanted to build a system to finally utilize them for what I bought them for. No drivers so far though, as for now I decided to dedicate my time just into the design and build of all the mechanical parts of the machine first.
For the mechanics I decided to go with the skate bearings rolling over 1 1/4" cold rolled steel square tubing as rails. For forming the basic structure of the table of the machine I decided to use these hollow square aluminum tubes I already had.
As I went building it all, I made many mistakes, into which I will not dig a whole lot along this follow up (but you can see them on the pictures), as the relevant ideas are the ones which stick (until bettered by new ones) and I prefer to concentrate on them.
I have been progressively making the 3D design using Google SketchUp, along with constructing the actual machine.. maybe not the cheapest approach cause some built parts which I decided to sacrifice for better designs, became unused, a fact in which some money and time can be lost, however I believe that one can learn a lot more by actually trying the stuff out in real life, rather than pure design first. Thus, the first 3D design was scratched and redesigned to match the ongoing one, as you can see on the attached pics.
I then started to pay visits to a local metal shop, asking them to cutout specific sized 1/4" steel plates and angles.. unfortunately they do not have a great deal of equipment to preciselly cut the stuff, so I had to ask them cut the pieces a bit bigger, and then spend a lot of time grinding the plates to size myself with an angular grinder.
The basic materials used so far in this design are: Aluminum hollow tubing 1 1/2" x 1 1/2", 1" x 2", Cold rolled steel square tube 1 1/4" x 1 1/4" and 3/4 x 3/4", Steel angles of 1", 1 1/4" and 1 1/2", Steel plate of 1/4", 22mm OD bearings, Machine screws: 1/8, 5/32, 1/4, 5/16 along with same sized nuts and taps.
I include pics of the so far progress of the construction and will continue to post more photos as parts are being made.
I didnt find the first design to be as stable as I thought it would be. I realized that for the size of the gantry, the bearings were not spaced apart enough (only 7 cm), as well as there was too much space between the bearings contact with the rails and the actual gantry walls. On the new design, the bearings are 14 cm apart from each other, are much more securely fastened to the steel plates of the gantry walls, as well as closer to them. This allowed for a more stable and robust coupling between the rails and the bearings, as well as the use of 4 bearings per side as opposed to 6 used in the first design. There are also less weak points in the newer design, as all I would need to do is couple together tight both sides of the gantry, to make it sit tight on the rails (adjusting the rails alignment). First design had many more adjustment points i had to "fine-tune" within the bearing blocks themselves for proper coupling between rails and bearings.
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Design and build of a metal structure 3 axis CNC router.
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