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  • Author Author: ralphjy
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Genmitsu CNC 3018-PRO - becoming useful

ralphjy

I had a minor victory on my road to figuring out how to use my new CNC router.

 

I received the 0.5mm carbide end mills that I bought on Amazon and used one to successfully shorten a proto PCB that I need for my LoRaXes project.  The mill has about 4 mm of cutting depth.  The PCBs that I'm cutting are nominally around 1.6 mm thick.  Not a very impressive looking cutter but it worked.  I increased the spindle speed to 3000 RPM and reduced the feedrate to 80 mm/min and set the cutting depth to 0.15 mm per pass.

 

image

 

Here is the shortened PCB next to one that is uncut:

image

 

The cut edges are very smooth but you can see that they are not quite straight.  Not sure if I can improve that with tweaking or if that's the inherent limitation of an inexpensive router and cheap end mills.  Only time and experience will tell.  Anyway, I'm pretty satisfied with the outcome.  The tool did what I needed it to do. 

  • in reply to balearicdynamics

    Hi Enrico,

     

    Thanks for the valuable information, this is really helpful. Also, I'd forgotten about the spindle motor : (

    Let's start a topic somewhere (called "CNC interface board ideas" or something) and we can continue there. It's great to be thinking the concept as we are, between us all first, so we can have a useful design.

  • in reply to shabaz

    Hi Shabaz,

     

    In my opinion, the scenario 2 should be excluded, while the scenario 1 is perfect. I try to explain my point of view:

     

    As a matter of fact, independently by what is the real power of the stepper motors (and the spindle), the logic should always be separated by the power stage. At least for two reasons: one is to avoid any kind of electric and electronic risk, the other is to have the same logic able to control any kind of motor. That is the scenario 1.

     

    The same signal sequence (A- B- A+ B+ on a bipolar stepper) will generate a step in one direction, in another direction or stopped but not freed. Then if you have a small 1A max stepper you can use half-bridges like ULN2003 or 2004  if the power is under 2.5A (peak). If you should control up to 5A (if I am not wrong) you can use an L298 like those stepper motor controllers yo find almost everywhere for 5$ or less.

     

    With high power motors (over 10A) you should use a more powerful motor controller, possibly that has its own high power logic able for example to manage microstepping and so on.

     

    For Nema17 (those you find in the 3D printers, the home laser engraver, etc.) a small half-bridge is sufficient. To make my The Lino Project with Arduino Mega 2560: Interrupts and Motors I had to use high torque stepper motors so I used a Moon's high power stepper motor (it costs about 60$); as you can see in the images, in the high power session (that should reside in the moving engine) wires are 1mm and can be also bigger if the power is higher. But also the logic level can control these.

     

    On the logic side instead, the same board, as you suggest in scenario 1, can control with the same efficiency and precision the stepper of the head of a CD driver as well as one of those motors.

     

    The connections between the logic and the power session (the drivers and motors) can be done as you prefer, possibly with a cheap solution. My RS3020 (Chinese optimization) for example uses multi-cable like those for the printers and a screwed Philips connector. And it works for years.

     

    Similar is the case of the spindle or, generically, high power and high speed (30.000 RPM and more) DC motors. These are connected to an inverter. A sort of PWM to PWM interface you can program on how much power you should send to the motor at a certain frequency and what speed (expressed in inverter frequency) the motor should run respect to the PWM of the logic board. And other parameters too. But the principle of separating the power stage is respected as well.

  • in reply to shabaz

    shabaz,

     

    This looks pretty good.  I am wondering if this is going a little too far off of topic on Ralph's post?  Maybe we should take this conversation into it's own thread?

     

    Gene

  • in reply to balearicdynamics

    Hi Enrico (and everyone),

    Here's some ideas, it would be interesting to know what you think, maybe the idea isn't feasible or there are better ways. Also, I don't know what features/connectors are useful.

    I'm currently thinking maybe have an "Interface board" that can connect to external drivers in scenario 1, but can use small stepper PCBs (some off-the-shelf one, to be determined) in scenario 2.

    For scenario 1, the configuration jumpers direct the BBB pins (via buffers) to the RJ45 sockets (are 4 enough?).

    image

    For scenario 2, the jumpers are placed so that the BBB pins for the drivers are routed through the edge connector instead, like a pass-through.

    This way, the same RJ45 can be used for direct motor control in scenario 2. It would result in a low-cost stepper driver carrier board that could be swapped out for a new design if low-cost stepper driver boards need upgrading to more powerful ones. It could be a new open interface : ) so anyone can design carrier boards for their favourite stepper driver chips/boards.

     

    image

    I can't think what connectors could be useful for power.. maybe RJ45 again, but with 4 wires for ground, and 4 for positive. Not sure! All ideas welcome, this is just a concept, and I'm not very knowledgeable in this.