The PCB mill is a very useful tool for cutting PCBs, but by its nature it also works very well for soft metals and composites. We can leverage this and use this machine to cut fiberglass and other composite fins. This doc covers how to perform this operation on the PCB mill in The Construct.

NOTE: Cutting wood fins on this machine is NOT recommend. if they are under 1/2" thick, you can simply laser cut them. If they are 1/2" thick or above, look into using the CNC router.

NOTE: This process can also be used for composite bulkheads.

IMPORTANT NOTE: This doc is made for using FlatCAM version 8.991. FlatCAM is a living software, and changes are made all the time. If using a newer version, the process may be different. If you want to follow this doc exactly, there is a download link for FlatCAM version 8.991 on the wiki.

Steps

Save fin geometry from OpenRocket as PDF.
1. File → Print/Export PDF → Only check "Fin Templates" → Save as PDF
Import PDF into Inkscape.
Select the fin, and use the keybind CTRL+SHIFT+G to ungroup the fin from the ruler scale part (if it is present).
Delete the ruler scale part, if it imported with it. If not no worries.
Verify that the fin is correctly sized.
1. Inkscape allows you to measure the outer rectangular perimeter of a part by clicking on it, use this to verify.
2. Moving the fin shape nearer to the bottom left of the page will help you later.
3. You can also just resize the page to your fin shape by selecting the fin shape and going to "Edit → Resize Page to Selection".
Save fin as DXF.
1. IMPORTANT NOTE: When saving as DXF, an options box will come up, where you can pick the unit to save your file as. Make sure the unit is set to millimeters (mm).
Open FlatCAM.
Import fin into FlatCAM.
1. File → Import → DXF as Gerber Object
Double click on file in tree navigator on left hand side.
Set tool diameter to the diameter of your end mill (units are mm).
1. NOTE: Default units in FlatCAM are mm.
Click "Generate Isolation Geometry".
You will see an isolation geometry path follow both the outside and inside of the fin. We only need the outside, so we will need to delete the inside line.
Navigate to the project tab, right click on the geometry object, and click "edit".
Select and delete the inner line.
1. Now is also a good time to make sure that the fin is positioned close to the origin, you can use the move tool on the right hand side to do this.
2. The fin should be just above and to the right of the origin (NOT intersecting the x or y axis).
3. If you adjusted the fin location in the Inkscape file earlier this should be fine.
CTRL+S to save the geometry object.
Double click on your geometry object.
Set "Cut Z" to the thickness of your material plus 0.03".
1. Make sure to convert this number to mm before you put it into FlatCAM.
2. The extra thickness is to account for tolerances of the material and any errors in z levelling.
Set feedrate and multi depth passes as necessary.
1. Feedrates of 90 to 120 mm/min with a depth per pass of 1mm works well for fiberglass.
Click "Generate CNCJob object".
Ensure that the path looks good, then click "Save CNC Code".
Connect to PCB Mill via USB and open up UGS (Universal Gcode Sender).
Set port, set baud rate to 115200, set firmware to GRBL, and click "Open".
1. You will need the CH340 driver on your pc if you do not have it already. The driver can be downloaded here.
PCB mill will open in an alarm state, click the "$X" button to release it from this state.
Attach material to bed of PCB mill, install end mill.
1. Various methods to attach material.
2. Best known method is blue tape on bottom of material, blue tape on top of PCB mill bed, superglue between. Strong hold and easy removal/cleanup.
Move end mill to proper X and Y location, Set zeroes by clicking "Reset X Axis" and "Reset Y Axis" respectfully.
Set z zero position.
1. Best known method is to do the "paper trick". Google this if you are unfamiliar.
2. The "Reset Z Axis" button will reset it.
Enter your gcode into UGS using the "Browse" button.
Activate the spindle by turning the knob on the PCB mill.
Run your gcode using "Send".
1. It is useful to set your z zero to a set position above the material and running your gcode first, to ensure everything runs as expected before you start cutting material.
Success!
1. You will need to vacuum up all that dust after the part has run. The PCB mill has a vacuum built in. Toggle the foot pedal attached to the left of the machine to turn it on/off.

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