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5. Electronics production#

Group: Make a Test PCB…to understand the procedure for milling a PCB using the Roland SRM-29 Milling Machine and understand the milling tolerances#

  • We cut a “Test PCB” to understand the capabilities of the lab’s PCB milling machine…the Roland SRM-20
  • We hope to understand what the “Inside” and “Outside” milling tolerances are for the machine
  • We used 2 endmill bits to cut the “Test PCB”…one for etching traces (1/64” dia, very delicate), one for cutting the board out of the larger PCB material board (1/32” dia)

We used Mods to generate the RML file needed by the Roland SRM-20 to cut out our board. The Mods command procedure to launch the are as follows…#

  • Right mouse click in the window…
  • programs > open server program > Roland > SRM-20 > PCB

In the Roland SRM-20 PCB Mods program structure we…#

Note: The Kamakura Node’s PCB Milling machine is NOT connected to the network and the server directly…therefore we first had to tell Mods to write the final RML file to a file on the local PC. The procedure for that as follows…

Instruct Mods to output the RML file to the local PC…#
  • In the Roland SRM-20 Milling Machine module in the lower left hand side, we specified output to a file by…
  • Right clicking in the Mods window > modules > open server modules > file > save

  • A new “save file” module created…we then linked it to the “outputs/file” of the “Roland SRM-20 Milling Machine” module by…

  • Left clicking “file” in the “outputs” box then left clicking “file object” in the “inputs” box of the newly created “save file” module
Uploaded a PNG file and converted it to an RML file…#
  • “Read PNG” to load the image of the “Test PCB” board…first “linetest.png”, the “traces” to be etched onto the board face…then “linetest.interior.png” to cut the outline of the board (why…does the name contain the word “interior” when we are cutting the outline of the board???????)
  • (The following images are representative, shows a similar conversion of a different PNG file)
  • Then we “Set PCB Default” parameters for “mill traces (1/64)”…noting “tool diameter (in)” = 0.0156, cut depth (in) and max depth (in) both set to 0.004 (the PCB board thickness is ~0.070 in), offset number (the number of cut passes to the sides of the traces?) set to 4…click “mill traces (1/64)” to send the parameters to the next module…”mill raster 2D”

  • In the “mill raster 2D” module, we make note of the various settings…in particular, we note that “offset stepover” is = 0.5 which we understand to mean that each cut pass offset will occur at half the diameter of the endmill bit

  • We note that mill rotation direction designated by “climb” (drill up) or “conventional” (drill down), as well as, Path Order “forward” (clockwise) or “reverse” (counterclockwise) can be specified for the milling
  • No one seems to know what “path merge = 1” means…
  • After observing but without making changes to settings…we click the “calculate” button to convert the PNG file to an RML files
  • …a preview image of the RML file appears below…this simultaneous autosaves the RML mill path file to local PC (upload folder for Windows, xxxxx?? for Mac OS)

  • We repeat the process to generate the cut path of the outline of the “Test PCB”

  • The main difference is the selection of the “mill outline 1/32” button in the “set PCB defaults” module (since we are cutting thru the board, a bigger endmill bit can be used)
  • Other differences include…changes to cut depth (0.024), max cut dept (0.072) and offset number (1)

  • We inspect the generated RML cut path files in the “view toolpath” module at the bottom by clicking “view”…and a 3D representation of the cut path appears

  • We open the generated RML files in a text editor to check for errors…which would appear at the bottom of the file…no errors seems to have been generated

  • We also note that the code at the bottom of the file is the same for all the RML files generated…these codes are specific to our Roland SRM-20 Milling Machine
  • Everything looks good…so we send the RML files to the PC connected to the Roland SRM-20 Milling Machine to cut our “Test PCB”
Milling the PCB#

The Roland SRM-20 Milling Machine…and other tools for milling

  • Two endmill bits 1/64 and 1/32 diameter (in red plastic containers)
  • Hex wrench to insert/remove the endmill bit from the milling machine
  • A brush to remove milled waste from the top of the PCB
  • Solvent to make the milled PCB removable from the sacrificial player
  • A metal spatula to remove the PCB from the sacrificial later (…we discovered that a smaller spatula with a thinner flexible blade was better for removing the small delicate PCB)

  • Replacing the endmill bit requires some delicacy…a small hex nut on the side of the chuck must be loosened to remove the in-place bit, then the bit must be gently removed/inserted taking care not to damage it…retighten the hex screw once the endmill bit is inserted

  • We had some trouble with seating the endmill bit into our machine…something wrong with one of the chuck collar for our milling head…good thing we had a spare

  • This is the control panel for the Roland SRM-20 Milling Machine…we used the arrow buttons to move the milling head in the X, Y and Z directions

  • When a good XY origin point for milling (starting from the lower left corner of the part)…we clicked the “XY” button under “Set Orign Point”…easy
  • To set the Z origin…the milling head to a location closer to the center of the PCB material (we were told that repeated milling ruins the leveling of the milling surface and it was best not to zero the Z near the edge of the PCB material )…we then carefully lowered the endmill bit head to within about 1cm of the PCB material before loosening the hex screw and letting the endmill bit GENTLY drop to the surface of the print material…tighten the hex nut…click the Z button under “Set Origin Point”…then raise the endmill bit head at least 3cm above the PCB material surface (this prevents any accidents as the mill spins up to operating speed ahead of actual milling)

  • Click the circular “cut” button near the bottom right of the control panel to mill…a last dialogue box pops up, we clicked “output” to begin milling the interior traces

  • Load the RML file for the outline of the board and repeat the steps to mill the outline of the board but DONT CHANGE THE XY ORIGIN!!!…after changing the 1/64 endmill bit out for the 1/32 endmill bit and re-establishing the Z origin point again

After the milling of the interior traces and outline is completed…

  • Squirt some solvent over the milled PCB

  • Peel the “Test PCB” away from the sacrificial layer using a spatula

Team A: observations#

●About scrap data

●Result of scrap

●Compare the two results

scrapable width = 0.016inch or more
         0.0156 inch or less will not be cut automatically
         (0.0156 inch = Mill’s size set on mods)
Leaveable width = 0.004~0.007inch or more  
         0.007 inch or more is good with a margin

Team B: observations#

  • Inspect the “Test PCB”…
  • Interior milling is possible up until about 0.016 minimum trace width
  • The trace width itself was successful all the way down to 0.001!!! Surprisingly thin!!
  • The cut depth seems deeper visually than 0.004…but no way to be certain