readme-isolation-milling.md

  
NOTE: This file is deprecated, captures info from when trying to do isolation routing of traces instead of chem etching.


TODO


[] Infill should not retrace.  Do bi-di laser cutting.
[] G2 format is wrong.  Getting rejected by LaserGRBL as an invalid code.


Proper G2: From wherever you are, you will start. Specify the XY end point withing the G2 command.  I&J represent the center delta from the start point to the end of the arc.



Another project: <![CDATA[]]>https://sourceforge.net/p/pygerber2gcode/code/ci/master/tree/<![CDATA[]]>

PCB Milling

<![CDATA[]]>Good overall resource<![CDATA[]]>

KiCAD

KiCAD Gerber export: disable the "Use extended X2 format" option.

PCB2GCODE


This tool worked great for generating G-code.


Much easier to use than FlatCAM.
Man page in file pcb2gcode.pdf.

Example config file: millproject
Generate code by running pcb2gcode in the same directory with millproject.
Use a short list of drill sizes, or it will use exact drill size for each part.  That can lead to a lot of tooling changes.
You can get some parameter by editing and running pcb_calcs.py.


The copper layer is very thin.  Got nice isolation with a margin of 0.5, could probably go lower.
This calcs the Z depth for drilling and edge cuts to cut into the tape.  It can be a bit tricky if you don't apply the height map.  Not clear if you can apply the height map to multiple files.

Bridges shouldn't be necessary if you don't cut too fast on the edge cuts.
Example call: <![CDATA[]]>https://gist.github.com/bullestock/87ed51aaadaae8b8d2f085756652eb04<![CDATA[]]>


Mounting PCB

It is very important to get the board as flat as possible.  The painters tape glued together does seem to work well if:
* Mounted to the aluminum plate, not the MDF spoilboard.
* Clean the aluminum with isopropal alcolhol ahead of time so tape adheres well.
* While glue is drying, put a large weight on the PCB.  A 5 lb sledge hammer worked well.

Tooling

The 60 degree triangular V-cut bits worked very well.  Robust bit, and isolated nicely.
* <![CDATA[]]>Inventree<![CDATA[]]>
* <![CDATA[]]>Amazon<![CDATA[]]>

Autoleveling


Use CNCjs autolevel module: <![CDATA[]]>https://github.com/kreso-t/cncjs-kt-ext<![CDATA[]]>


This is loaded on the Shop Server, in the CNCjs VM.
It's in directory ~/tmp/cncjs-kt-ext/
It must be restarted every time the USB connection is made.


>> node . --port /dev/ttyUSB0

Create a macro or run from the command line:


(#autolevel D7.5 H1.0 F20)
F - Z-probe speed, don't go lower than 20 (mm/sec).
D - Grid spacing.  Defaults to 10 (mm).




Soldermask & Silkscreen

Intended process is to apply two layers of soldermask/ink to the PCB, then use my UV laser to ablate the areas that I don't want filled in.  Overall technique from: <![CDATA[]]>https://www.youtube.com/watch?v=NuJlgw7E7vg<![CDATA[]]>.

Soldermask goes down nicely with:
* Cover with plastic film (overhead film works well). Need rigitity.  Plastic wrap is too soft.
* Use a squeegee to spread the ink.  I used Silicone squeegee from <![CDATA[]]>Amazon<![CDATA[]]>.
* Cure with UV light.  I use a resin printer cure station for 3 min with board leaning against lamp.

Essentially:
1. Lay down & cure the base soldermask (color of choice)
2. Ablate soldermask in areas where you want silkscreen.
3. Apply white ink/soldermask & cure
4. Ablate solder pads: 80% power, 200 mm/sec

Software Tooling

While FlatCAM is a very impressive piece of Python GUI software, it's cumbersome to have to do a lot of manual stuff.  Per above, PCB2GCODE does a great job with the isolation routing, edge routing and drilling G-code file generation.  Once you've properly parameterized your system, it's a two second opeation to go from Gerber to G-Code.  Looking to add in the next steps in that tooling for laser ablation paths.

We need to go from Gerber to G-Code. <![CDATA[]]>Gerbonara<![CDATA[]]> can read Gerber files and provide graphics primitives which can be converted to G-Code by a custom Python module gbr2grbl.py.  This is able to draw and fill rectangles and circles, which meets the most basic of soldermask needs.

With a "dumb" implementaiton, just generating G-code geometry,
* With 0.1mm infill step size, CAMotics estimates:
    * Job time: 1m 21s
    * Total distance: 1378.1 mm.
* No infill
    * Job time: 15s
    * Total distance: 239.2 mm.

With 2D position scheduling optimization
* With 0.1mm infill step size, CAMotics estimates:
    * Job time: 1m 18s (3.7% savings)
    * Total distance: 778.0mm (43.5% savings)
* With no infill, CAMotics estimates:
    * Job time: 14.9s (0.7% savings)
    * Total distance: 222.1mm (7.1% savings)

With Traveling Salesman optimization (greedy tsp):
* With no infill, CAMotics estimates:
    * Job time: 14.93s (0.7% savings)
    * Total distance: 227.4mm (7.1% savings)

To do:


Looks like need to flip bottom side image.
Verify home position is correct.
Add in laser G-code parameters as TOML config file.
Add generation of other g-code files handled by pcb2gcode (drill, edge route, isolation route).
Parameterize pcb2gcode to use the same TOML config file.
Use .gbrjob data for pcb2gcode config.  Stackup has PCB and Cu thicknesses.
Make sure I have the stackup config correct in the KiCAD PCB file.


Overall Process

Note: For all operations, keep grbl software running and maintain XY home position.


Mount bare PCB to a flat but sacrificial material which is clamped to the mill bed.  PCB mounting via glued tape attached to both surfaces.  Doublesided tape will work well also.
If the PCB is double sided, drill corner holes that can be fitted with dowell pins for locating.
Autolevel board
Isolation route PCB back side.  Start with back side to minimize flips (assuming silksceen is front side only).
If double sided: clean PCB apply and cure back side soldermask, flip board, repeat steps 3 & 4 for front side.
Clean PCB, apply & cure soldermask.
Mount laser.
Ablate silkscreen image.
Apply & cure silkscreen ink
Ablate soldermask for solder pads
Remount spindle
Drill
Edge route
Tin exposed pads.