Using the CNC mill

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Warning Warning: Don't mill printed circuit boards made of "glass fiber epoxy resin" (FR4). Small pieces of milled glass fiber should not be inhaled. It may cause health problems.

1. Designing the PCB

There are several ways for designing PCB. For example you can use the following softwares:

Lets start with Fritzing.

All the Fritzing Tutorials
pcb design basic tutorial
Designing a custom shape pcb

Pcb.png

That looks already quite good. After you finished the PCBs you have to export it as a "Extender Gerber (RS-274X)"-Format! Select the folder where you would like to save it.

Gerber.png

2. Generating the G-code

In this step you have to generate G-code with the Gerber files. G-code or sometimes called nc-code (numeric controll code) tells the CNC mill when to turn on the spindle or to which position it should move.

We will use FlatCam (http://flatcam.org/) to generate the G-Code. The Flatcam manual

  • Start FlatCAM
  • Go to Edit -> Preferences and make sure measurements are set to millimeters.

To mill a circuit board, we will need to make three separate files, the traces, the holes and the contour.

TRACES

First for the traces:

  • Click on [File] -> [Open Gerber ...]
Flatcam.png
  • Select the ".gbl" (copper bottom) file
  • Now select the file in the Project list and click on [selected]
Selected.png
  • drag in "copperBottom.gbl"
  • Double click on the Gerber file to go to the Selected tab.

Set the Tool Settings to:

  • Tool dia: 0,5000
  • #Passes : 1
  • Passes overlap: 0,00000%

and Click "Generate Isolation Geometry"

Here we will set the millings settings.

Under Parameters for Tool 1

  • Cut Z: -0.0800
  • Uncheck Multi-Depth (default)
  • Travel-Z: 2,0000 (default)
  • Uncheck Tool Change (default)
  • End-move Z: 50,0000
  • Feedrate X-Y: 120,0000 (default)
  • Feedrate Z: 60,0000 (default)
  • Spindle speed: 0 (default)

Click on "Generate CNCJob object" and "Save CNC Code"

<HOLES>

To drill out the holes, we'll need to import your drill.txt file. Go to Files > Open > Open Excellon and navigate to your drill.txt file.

Go to Project and double click the "drill.txt" under Excellon.

The settings for the drill bit are:

  • Cut Z: -2,0000 (default)
  • Travel Z: 2,0000 (default)
  • Uncheck Tool Change (default)
  • End move Z: 50,0000
  • Feedrate Z: 30,0000 (default)

Click "Create Drills GCode"

If you see huge yellow circles , lower the size to 1 if you see huge yellow circles underneath the "CNC Tools Table" and click "Update Plot".

Scroll down and click "Save CNC Code".

CONTOURS

Lastly we want to mill out the shape of the PCB.

Go to File > Open > Open Gerber and navigate to "contour.gm1"

Open the file and double click it to go to the "Selected" tab.

Select "Cutout Tool"

Object to be cutout: "contour.gm1"
Object kind: Single (default)

  • Tool Diameter: 1
  • Cut Z: -1,8 (default)
  • Check Multi-Depth: 0,6 (default)
  • Margin: 0 (default)
  • Gap Size: 2
  • Gaps:4 (default)

(not necessary if your circuit board is taped to the sacrificial layer properly, but if you don't mind breaking some tabs it's a safe option)

Now select "Generate Freeform Geometry" 

 Tools Table:

 1,0000 | C1

 Parameters for Tool 1:
  • Cut Z: -1,8 (default)
  • Multi Depth: 0,6000 (default)
  • Travel Z: 2,0000
  • End move Z: 50,0000
  • Feedrate X-Y: 120,0000
  • Feedrate Z: 60,0000
  • Spindle speed: 0 (default)
  • Uncheck Dwell (default)
  • Postprocessor: default (default)

Now select "Generate CNCJob object"

and click "Save CNC Code".

Flatcam 8.991 Overview
There is a good, concise tutorial for this Flatcam version here Flatcam single layer pcb tutorial

Flatcam overview.png

3. Milling the PCB

Srm20.png

Start the program "V-Panel for SRM-20", make sure the mill is turned on and the lid is closed.

TRACES

We'll start by milling out the traces. To do this, we need to make sure the V-shaped bit is installed in the CNC. The V-shaped bit can be found in the CNC box and should look like this:

We start installing the V-shaped bit by moving the CNC-head all the way up. In V-Panel, you can do this by pressing the UP arrow with "+Z" next to it.

When the CNC head is all the way up, replace the mill unscrewing the screw holding the mill bit on the side of the CNC-head.

Now install the V-shaped bit and tighten the screw with the hex key.

Calibrating the CNC

To properly mill out the traces, we need the CNC to know where the face is it needs to mill. To do this Change the Machine Coordinate System on the top left to G54:

Machine Coordinate System.png

and move the Mill all the way to the bottom left corner of your copper plate using the arrows.

ArrowsOfV-Panel.png

Now drop down the mill with the Z-arrows until almost touch the surface. !! Be careful not to hit the surface!! You will break the mill.

ZARROWS.png

Make more precise adjustment by changing the Cursor step.

CursorStep.png

When you are as close as possible to the surface. Unscrew the mill with the small hex key, let it drop

TOUCHINGZ.png

and tighten it again.

TIGHTENINGHEX.png

Now set the new origin point to G54 and click X/Y and Z.

NewOriginPointCNC.png

X, Y, Z should now be 0, 0, 0.

0,0.png

Milling the Traces

When you've properly calculated the CNC for your copper plate, the mill bit should move the the bottom left corner when you press "X/Y" and "Z" under the "To Origin" tab.

If this is the case, we can start milling the traces.

Close the lid of the CNC and Press "Cut" > "Add" > and look for your "copperBottom.nc" file (or whatever you've named it).

Now press "Output" and the CNC should start milling out your traces.

HOLES

Next, we'll drill out the holes. For this we need to swap out the V-shaped bit for the drill bit. The drill bit should look like this:

The CNC should have ended it's milling with Z : 50 so it's easy to replace the V-shaped bit for the mill bit with the small hex key. If you cannot reach it, try closing the lid and moving the Mill bit around to a place where you can reach it.

When you've swapped for the drill, you need to calculate the Z-axis again, but not the X/Y . If you loose the X/Y values, you will not be able to drill the right spots on your circuit board!

Press "X/Y" under "To Origin" and follow these calculation steps again:

Drop down the mill with the Z-arrows until almost touch the surface. !! Be careful not to hit the surface!! You will break the drill bit.

ZARROWS.png

Make more precise adjustment by changing the Cursor step.

CursorStep.png

When you are as close as possible to the surface. Unscrew the mill with the small hex key, let it drop

TOUCHINGZ.png

and tighten it again.

TIGHTENINGHEX.png

Press "Z" under "New Origin Point" (NOT X/Y).

NewOriginPointCNC.png

X, Y, Z should now be 0, 0, 0.

0,0.png

Close the lid of the CNC and Press "Cut". Select the existing files and click > "Delete" and click "Add" > and look for your "drill.nc" file (or whatever you've named it).

Now press "Output" and the CNC should start drilling out your holes.

CONTOUR

Now let's mill out the contour to give the circuit board the shape you like. To mill out the contour we'll need to use the mill bit. It looks like this:

I'll repeat the steps again for the sake of consistency.

The CNC should have ended it's milling with Z : 50 so it's easy to replace the V-shaped bit for the mill bit with the small hex key. If you cannot reach it, try closing the lid and moving the Mill bit around to a place where you can reach it.

When you've swapped for the flat mill, you need to calculate the Z-axis again, but not the X/Y . If you loose the X/Y values, you will not be able to drill the right spots on your circuit board!

Press "X/Y" under "To Origin" and follow these calculation steps again:

Drop down the mill with the Z-arrows until almost touch the surface. !! Be careful not to hit the surface!! You will break the drill bit.

ZARROWS.png

Make more precise adjustment by changing the Cursor step.

CursorStep.png

When you are as close as possible to the surface. Unscrew the mill with the small hex key, let it drop

TOUCHINGZ.png

and tighten it again.

TIGHTENINGHEX.png

Press "Z" under "New Origin Point" (NOT X/Y).

NewOriginPointCNC.png

X, Y, Z should now be 0, 0, 0.

0,0.png

Close the lid of the CNC and Press "Cut". Select the existing files and click > "Delete" and click "Add" > and look for your "drill.nc" file (or whatever you've named it).

Now press "Output" and the CNC should start drilling out your holes.


The V-shaped bit is used for milling out the traces and the mill bit for the holes and contours. The V-shaped bit needs the big socket and the mill bit the medium sized one.

You calibrate the bit bit installing it. Going all the way down, as far as you can and undoing the screw inside the socket to loosen up the bit. It will drop down as far as it can. Tighten it again, and press the "Z" button on the right (at Set Origin Point)". You can do the same for X/Y axis if you want the script to start at a specific point.

When the CNC is calibrated, select the "Cut" button on the bottom right and Add your .NC file. Press output to start the Milling. Mill your traces first, then your holes and then the contours for the best stability and do all of these individually so you can switch bits in-between.

Good luck!

Vpanel01.png

5.Trough-hole pcb with Fritzing for Mods

As mentioned, when using Kikad or Eagle it is relatively easy to export each layer as a .svg or .png file, when using Fritzing and having a through-hole component, we will use a slightly more bulky pipeline. In Fritzing it is all very straight forward if you have only surface mount components, but gets complex to export an image file with just holes.

Thus we go through a slightly more complex pipeline of two more pieces of software.

We will export gerber files from Fritzing

Fritzing export gerbers.png

Then we will use a gerber viewing software (Gerbv [1]) or gerberlogix (https://www.easylogix.de/products_detail.php?prog_id=1) to view our

  • bottom copper .gbl file
  • our contour .gml file
  • our drills .txt file


We will then export each layer we need as separate image files (.png or .svg)

Gerbv

And then last, before we can go to Mods we will use Gimp or Photoshop to convert images to black and white and also do some editing if we have a ground pour. Only then, we will move to Mods.

Tutorial: Surfacing the CNC bed


4. Using Mods

Alternatively we can use Mods (web based software from Fab Academy) to generate paths from .SVG or .PNG files
When using Kikad or Eagle it is relatively easy to export each layer as a .svg or .png file, when using Fritzing and having a through-hole component, we will use a slightly more bulky pipeline.

Mods project is a module based software with a web interface that already has a SRM-20 preset
Here is a good in depth tutorial how to use it but bare in mind that the interface has changed a bit and you may find differences
Here is an even longer tutorial including the finishing and soldering of a board

how to prep a file in eagle

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