My need for a mechanical solution started with the realisation that I could not cut things accurately by hand!
As I initially wanted to create a set of railway carriages, it relied upon repeat accurate cuts which apart from not being able to do seemed extremely time consuming and boring.
After researching the web, I discovered CNC. I have had a long time ambition to start a hobby for retirement and model engineering was my answer. I have no training or practical experience in any of the skills needed for model engineering. Building a CNC machine seemed to be a good starting point. (I'll need lots of help in the electrical bits )
I realized that a CNC machine would enable the repeat accurate cuts that I needed, however I also realized that I could build a tool that satisfied the above need but that tool could also become very limited unless I designed with future projects in mind. So my imagination took over and I thought of a long list of wants that this machine could achieve.
One thing that seemed obvious was that if I build a small machine, I would get frustrated by its limitations and that as soon as I finished the first I would want a second. I also argued that a small machine does not imply increased accuracy or reduced complexity, just reduced outlay. So if the choice was two machines or one machine, then one large machine made better sense even thought the initial investment is high.
That left me with a whole heap of design criteria such as: size of cutting footprint, thickness of material to be cut, type of material to be cut, etc.
Furthermore, I realized that these machines could wear a whole range of adaptations such as lasers, air brushes for painting, die grinders, belt sanders, orbital sanders, jigsaws, etc.
Also, I could experiment with cutting glass, stone, metals, plastics, etc.
I was not limited to 3 axes either and could incorporate a turntable or a swivelling head, etc.
I opted for a design that would take a standard sheet of material made of hardwood or aluminium whilst keeping my options open for more challenging materials. I also felt that 6in travel for z axis was a reasonable challenge, whilst allowing for additional axes to be retro fitted.
I then reasoned that a standard sheet of 2400 * 1200 seemed a lot of investment for something that was still basically a hobby. It was then that I decided upon modularisation. I decided to build a machine that would take 1200 * 800 with the ability to be converted to a 2400*1200 (that is 1200*800 + 1200*800 + 1200*800) easily.
With a modularisation target in mind, I concluded that I would have to have a gantry design as then, the only significant change from 800 to 2400 was the lengthening of the x rails. With a gantry, I am able to put the x, y and z motors all on the gantry.
So, I was committed to a footprint of 800 (x) * 1200 (y) with a 6inch z travel. That led me to be concerned about structural strength. I thought that a gantry supporting a router assembly spanning a cut of 1200 would require reasonable strength. Hence, I decided upon mild steel for all assembly. Apart from anything else, I wanted to learn how to work with metals including cutting, tapping, welding etc.
Also, I didn't like the idea of aluminium. I didn't think it would be strong enough and I was concerned about prolonged use introducing fatigue. As a person who knows very little I might be wrong on that consideration. I also thought aluminium would prove more expensive. (Still don't know ... haven't compared!!)
So, by deciding upon a machine of this size, I did not find out until much later that I had inadvertently committed myself to at least gecko level controllers and 400oz/in motors.
I had a long look at steppers and they seemed to be understandable. I had a long look at servos and they still seem like an absolute minefield.
Also, I had a long look at drive gear and compared threaded rod with timing belts. Timing belts seem a lot simpler for me so that is the path I have taken. Furthermore, with the possibility that my machine might be expanded on the x axis from its existing 800 to 2400, timing belt extensions are far practical to extend than threaded rod!
Also, it had to be elegant. I wanted to create a machine that looks simple and is a joy to watch. That means that I had to ensure that it looks balanced, designed with simple structures of triangles, circles, lines and rectangles
In summary, I realized that the design criteria I had set was for it to be elegant in design, robust, functionally effective, accurate and modular.
So, I have started this log to show everyone what I have created.
So far, it has consumed a heap of time (both thought and build) but when I compare with other logs, not that much money. Mild steel is cheap. I reckon the cost of the frame and gantry and head and router but excluding motors, controllers, drive gear is around $800 Australian. Three geckos ($450), 3 400oz steppers ($400), control box ($150), timing belt and gears ($200) will keep my investment to a total of around $2000 which I reckon is pretty cheap.
Furthermore, changing it from a 1200*800 to 2400*1200 machine will probably only cost me an extra $800.
Considering a finished model railway carriage in Gauge 1 could cost me $2000 then I reckon I'll be in front very quickly.... plus I'll have had the satisfaction of getting this machine finished and be able to use it for heaps of other projects.
At this point in time, I have been working on this for about 9 months. A lot of it is in semi assembly but I have now started to go back over it all from the beginning with a view to bedding down prior to proper assembly.
I have got some pictures and will soon get the first group on this thread in the next few days.
I hope this log will be of help and look forward to any feedback.
Andy