Since we're going to actually hack a pre-existing product - a shop bought CNC engraving machine - the first step is to assemble the CNC engraving/laser machine - it comes as a kit with instructions of it's own (see below). The upright aluminium 2020 sections need to be replaced with longer ones - 300mm - so that there is plenty of height for the vacuum needle. The engraving motor is not used and is replaced with the 27:1 stepper motor, which then rotates the SMT component (A axis). Fortunately, I was able to find a motor that fitted perfectly into the same hole so no machining was necessary other than drilling the four mounting holes. The instructions for the engraving machine assembly are HERE in the 'files' section.

Video for engraving machine assembly is here (this is NOT my work - we're going to hack this machine to do pick and place)

This step is slightly more difficult as it involves some machining. The microscope stand is turned upside down and the base plate machined with a hole big enough for the Z axis motor to pass through unobstructed.

Take the square base plate as in the photo below and drill holes to suit the stepper motor that fits above it:

The photo below shows it's final position:

The photo above shows the A axis motor on the right and the Z axis motor above, passing through the microscope mounting plate. The machining is best done on a lathe in a four jaw chuck although I actually used an industrial magnetic broaching drill. Another identical base plate can be mounted at 180 degrees to allow 2 microscopes to be used simultaneously. The use of 2 microscopes is highly recommended as accurate 3D positioning is very difficult without them both.

The arm attaching the microscope needs to be unscrewed from the banjo fitting on the vertical tube and carefully bent to exactly 125 degrees as in the photos below:

The needle assembly involves some basic machining on a lathe. The swivel banjo fitting allow the nylon vacuum tube to stay stationary whilst the needle is rotated and has 1/8" NPT threads. The brass tube on the left can be threaded with a hand tap but the brass adapter on the right is custom made on the lathe with a male 1/8" NPT thread so set the lathe threading gears to pitch 27. The other end of the fitting is machined with a slight taper to push and lock into the needles.

The PCB controller board was designed and fabricated from scratch and is dead easy to assemble and requires only basic soldering skills.

The Arduino Mega sits underneath the board at the top left and all the components have shapes drawn for their locations. There are a few small mistakes on the PCB V1.1 but nothing serious. There are jumpers to solder in for the Mega and the large 'Drill' circle can be ignored as it's for accessing the SPI headers.

Connect a toggle switch from 12 volts In to the big power supply bolted onto the board, middle left and adjust the power output voltage to what's required for the vacuum pump using a multi-meter.

There are extra slider, push button and rotary pot positions for other projects in the future. They're not required for this project.

The far left rotary pot is the speed control, the push buttons for selecting each motor. NB the top right push button is for a 'NULL' stepper motor and is effectively a travel reset. The sliders are for fine and coarse movement control. I mounted my controller on a bit of plywood using 1 1/4" no.4 screws and some plastic spacers to keep it from wobbling about during use.

The Arduino code is incredibly simple, with some strange looking oversampling for preventing the motors from vibrating:

void sampling()    //Oversample the slider readings to avoid motor vibration.
{
   i=0;
   val =0;
   smallVal=0;
while(i<100)
{ 
  val = analogRead(14)*multiplierLarge +val;
  smallVal = analogRead(15)*multiplierSmall +smallVal;  
  i++;
}
  val=val/i;
  smallVal=smallVal/i;
  totalVal=val+smallVal; 
  totalValInt=totalVal.toInt();   
}

  if((switchOneVal==HIGH)&&(switchTwoVal==HIGH)&&(switchThreeVal==HIGH)&&(switchFourVal==HIGH))
  {
  digitalWrite(12,LOW);
  digitalWrite(11,LOW);
  digitalWrite(10,LOW);
  digitalWrite(9,LOW);
  digitalWrite(8,LOW);
  digitalWrite(7,LOW);
  digitalWrite(6,LOW);
  digitalWrite(A0,LOW);
  digitalWrite(A1,LOW);
  digitalWrite(A2,LOW);
  digitalWrite(A3,LOW);
  digitalWrite(A4,LOW);
  digitalWrite(A5,LOW);
  digitalWrite(A6,LOW);
  digitalWrite(A7,LOW);
  }

See the files section for the full Arduino code.

WARNING:

• Never operate the controller board with the USB cable connected to a computer.
• Never connect the external DC supply with the USB cable connected to a computer.

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