Tuesday, 10 March 2015

My CNC story (part 2)

Please read the previous part first. This is the second part of my CNC story. Click here to find part 1. I will add pictures as soon as I have a little time later.

The first (but not the only) observed problem

One issue I discovered was that the motors occasionally skipped steps and/or added extra steps when they were running. Reducing the speed helped, but the problem with the extra steps and the skipping was not solved before the motors were slowed down to totally unacceptable low speed. I simply needed to do something; otherwise it would be pointless to build. Of course, I could easily identify the source of the problem, it was the controller card. I complained to the seller and he/she was kind enough to send me a new card. Unfortunately that meant another month wasted in waiting.

Mechanical works

In the meantime I continued with the mechanical design and buying some mechanical parts. During this process I realized that my home machinery is not enough, I had to buy some new ones or complement the ones I had. One of the things I did was buying a drill press stand, so I could drill straight holes repeatedly. This sounds basic today, but my limited mechanical experience didn’t make this clear for me before I started drilling holes in a larger scale.  The other thing I realized that to be able to drill with accuracy, the bench drill must stand on a very stable stand, preferably fixed to the floor, to avoid vibrations.

Work space, bench and tools

My space in my tiny home workshop is very limited, so I had to build a work bench especially made for that limited space. I attached it to the walls and fixed the bench drill stand to the bench so there is practically zero vibration when drilling. So, if any of you ever start a CNC build project, check out your work space first, check all the tools and machines you have, buy or make a steady work bench and a good drill machine. You will also need a circular saw capable of sawing the materials you are using for the frame and the other parts, which in my case is mostly aluminum. Of course, cutting plastic parts, steel and stainless steel parts is also necessary, as well as grinding and polishing things, so the machines don’t end up with a drill machine and a circular saw. Not only that, but small things like a good set of high quality drill bits and other small tools are also necessary to buy, and while individually they don’t cost a lot, adding them all up makes it into a nice sum. So, don’t start a CNC build project if you are not prepared to pay for all that, unless you already have a well-equipped home workshop.

The new controller card

After five weeks waiting my new controller card arrived. Initially I was very happy and couldn’t wait for plugging it to the motors, but my joy was quickly killed because it had the same problems with skipping and/or extra steps. I thought my analysis was wrong and was convinced that something else caused the issue. It didn’t take long to google and find forum sites where this card was mentioned as a card with very serious problems, similar to mine. So what’s next? I didn’t want to buy a new and different card, because there is no warranty that those would be better, I may end up with similar or different problems with a new card as well, only at even higher costs.

Solution to a real problem

I knew that I have a very high electronic knowledge and could fix this card, so I started measuring and documenting the work. This took quite some time, but have to admit, was challenging and interesting. In the end, I ended up with a total redesign of the card.

This can’t be true, was my first thought, so I did some more googling and found a site called CNCzone, where there was a long thread about this card and how people ended up with the same problems and found different solutions. Most people have given up, but some more or less redesigned the card, made a lot of changes to make it work. Some of the proposed changes were contradictory to others, some were directly wrong, so in the end, I trusted myself most, adopted only very few new changes from that forum since most of my redesign was right and was also implemented by some of those people. Never the less, it was great to find that site and useful to see that I was not alone. Anyway, the time went by and I continued building, concentrating on the control box and other electronics and learning all about programming CNC, using G-code and what it should be able to do.

Mechanical problems

After a while, and well after I was ready with the electronics, I got stuck with the mechanical design. I realized that regardless how I do it, with the aluminum profiles I was planning to use it will be too weak and I will not be able to get the precision I needed. Buying other type of profile would increase the costs to a level which I regarded far too high to make it worth making it, so the project stopped and was put aside.

Though, a few months later I started to see the light at the end of the tunnel.

Please continue with reading Part 3.

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