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Week 08 - Group assignment

The goal is to characterize some limits of our milling machine / mills

Prepare path in mods

We'll use the traces test provided by the fabacademy to evaluate the limits of a cylindric 0.4mm mill.

The png files of the PCB can be found on the fabacademy website:

Here's how to mill a PCB from mods on a Roland SRM20, using png files.

  • First open the web interface of mods mods.cba.mit.edu
  • Right-click anywhere on the white space to add a block: we'll start with programs -> open server program -> Roland > mill > SRM-20 > PCB png. A network of boxes appears on the canvas.

  • We can now import the traces file by clicking on select png file in the first block on the top left

  • To set the mill parameters, we can directly enter them in the mill raster 2D block, or chose one of the presets in the set PCB defaults box. For the traces we can click on the button mill traces 1/64, which will change the value in the mill raster 2D block.

  • We'll need to save our files locally, then upload them on the Roland SRM-20 computer through its dedicated interface. In order to do this we can delete the Web socket block and replace it by a save file block. To do so, first click on delete in the Web socket block, then right click on the blank space and create a module: modules -> open server module -> file > save

  • Link the save file block to the Roland SRM-20 milling machine block: click on the yellow box outputs file on the right of the Roland box, then on the inputs file yellow box on the left of the save file block

  • We have some parameters to change in the Roland SRM-20 milling machine block: the speed, and the home and origin coordinates. It's very important to set a z home above 0, like 15mm, to avoid hitting anything and breaking the mill:

  • Let's check the mill parameters, then click on calculate. A preview appears in the block.

  • We can open the preview in a new window by clicking on View. The generated path is automatically saved in .rml format (you should find it in your Downloads folder)

  • We're now ready to mill the rml file with a 0.4mm mill. Let's generate the edge cut path before carrying on with the proper milling.

  • Import the edge cut png file (the same way you did for the traces png).

  • Change the mill parameters. I used the preset mill outline (1/32)

I had issues when milling at that point (see below).

Milling

  • Turn on the Roland SRM-20 machine and open the interface from the computer.

  • In order to open and read correctly .rml files, you need to specify it in the interface preferences by clicking on Setup: select the radio button RML-1 (not the button NC / RML-1!!). You'll see that the coordinates menu is a bit different, you have no access anymore to G54 coordinates for example, instead you'll use the User interface coordinates.

  • Prepare your 0.4mm mill and zero it as usual (see individual page). Do the XY origin too.

  • Click in Cut, delete the previous files and add the .rml file corresponding to your traces.

  • Do the same for the 0.8mm mill, with the edge cut rml file... or not?? I broke the mill, so ended using a 2mm mill (that we use normally) with the same rml file. I'm really puzzled with how mods works (compared to FlatCAM), as the settings we use don't appear as clearly as in FlatCAM in my opinion.

Results

We can see that it was able to isolate all the thin traces (even the thinner ones), but not to do very thin cuts (.016mm is the smaller detail that was properly milled).