Friday, 29 May 2015

My CNC story (part 6)

Two steps forward and one step back.

Please read previous parts first. Click here to find part 5, here to find part 4, here for part 3, here for part 2  and here for part 1. As you may have noticed, I have started to add pictures to the previously written material also, so it might be a good idea to revisit previous parts even if you have read all those already. I will continue adding new pictures, and also video, as I find the time to do it.

Some serious words of warning

In part 5 I spoke warmly about a USB controller, which I truly liked from the start because it seemed to work nicely. Well, yes, it works well in an ideal environment, if you don't want to implement any auto tool setter feature, not use a vacuum cleaner and don’t switch on lights or other machines when the CNC is working. In other words, if you are still just a spinner or milling only air, not real material, and live in an optimal environment. In other words, this card is totally useless in real world, so if you plan to buy one, save the money and don’t bother.

I have also sent a warning to Artsoft, the company making and selling Mach3. It is wrong that they advertise this card, their recommendation made me buy it and waste my money.

In short, I gave up on this card and went back using the parallel port solution.

The problems

There are several issues with this card, but two-three major problems make the HyCNC USB card totally useless, and even dangerous for real work.

  • The G31 probing code is not implemented

    This is not working at all, since it is not implemented. If you enter for example “G31 Z-10 F100” then the Z should start to travel towards -10 and stop on contact with the probe. Nothing happens, no axis will move on G31. I have been in touch with the maker of the card and they promised to solve it but that never happened. I think they lost interest in this card or realized that the second problem is killing the product anyway, so they have just dropped it all together. What is even worse is that they made their own probe function.

  • The built in Z probe has serious bugs in it
    There is a built in Probe function but it is improperly implemented and is only working for the Z axis. In any case, the function is not usable because the axis will overshoot, in one of the possible modes down, right into the work piece, or if you plan to use the other mode then it moves extremely slowly down, stops when necessary and moves up but overshoots and sets the wrong offset. Totally useless.
  • The most serious issue

    An extremely serious issue which could cause fatal or serious injury to the user or destroy the machine is the extreme noise sensitivity of this card and the way it can behave in a noisy environment. I am talking about electrical noise, not something the user can do much about. Switching on a light in the room, or starting up a vacuum cleaner or another machine while the CNC is under power, or running, cause the CNC to run away totally uncontrolled. This is caused by the HyCNC USB card “spitting out” a huge number of step signals on any axis, or simply stops reacting to input signals. The results can be that the CNC movement stops on one or all axes or in some cases one or more axes starts using rapids, smashing the tool, the work piece or the CNC itself if you can’t manage to stop it and break the power. When the runaway occurs, the eStop is also out, so the only way to stop the movement is by breaking the mains power. Uncontrolled movements are rare but they have happened twice in real use, and a few times while I milled air.

Time to take a step back in development of my CNC

After these problems and after I have managed to identify the cause I decided to remove the HyCNC card all together and took a step back in my design and returned to use the ordinary parallel port solution. I don't like that solution because it is a dinosaur, but it is reliable and never caused any problems ever since. I can start any machine in the room, never ever noticed not even an extra step, let alone a runaway CNC. The only problem is that Mach3 is not working with any laptops, at least not mine, which is a fairly new HP, even though I have a parallel port in the docking station which every other software is capable to use but not Mach3. I don't know why that is, but right now don’t care about it much, I reverted back to using an old desktop computer at the moment.

WARNING about the HyCNC USB card

In conclusion, my advice is a warning to anyone planning to use USB, be prepared for problems. If you can continue using parallel port, do it. It is simple and reliable, so unless you need something else just stay with it and enjoy using your CNC.

My CNC is now ready

I aimed mainly at milling plastics (POM and acrylic) and also some PCB, but after I have used the CNC for a while, I am pretty sure it works well even for aluminum, though not tried yet. All in all, I am quite happy with my CNC. The maximum milling speed I get is 450mm/min and for the rapids (movements without milling) I can drive with up to 550mm/min. This is more than enough for such small machine in my opinion. The work area is 250mm x 350mm and the foot print of the machine is about 800 x 700 mm, with a total height of about 1500mm. It is quite high because I chose to make it that way, it is on its own stand and the four feet are on wheels, so I can fairly easily move it around. It weights quite a lot. Not measured but it is heavy. Planned for a table top version but ended up with a bit larger than necessary. Never the less, it works just fine and now, finally I can start using it for real.

Will post pictures and will describe the final machine later on and in another post.