CNC Mill

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Revision as of 12:00, 17 February 2024 by Blu (talk | contribs) (→‎Trace Isolation)
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CNC Converted Little Machine Shop Mini-Mill
CNC Mill .jpg

Location: Machining Area
Ownership: Breaks Everything (Loan)
Status: Fully Working
Usage Restrictions: Preapproval Required?

CNC Mill
Brand: Little Machine Shop

Model: UNIT-00
Coordinate System: Cartesian
Quality: Prosumer/Professional
Axis Travel: X: 120mm,
Y: 288mm,
Z: 210mm

The Mini-Mill is a loan from Mr. "Breaks Everything".

Standard Operating Procedure

CNC Instructions

   1. Turn on Computer
   2. Flip power Switch to up Position
   3. Turn Estop Clockwise 
   4. Login User: maglab 
      Password: magcat
   5. Click on “metric” or “merica” for metric or standard interface
   6. Click Home All (important, bad things will happen if you don’t
   7. Click on file on top left and click open navigate to your g-code file
   8. Click on help for help menu
      

Notes:

   • Do not store g-code locally use USB drive
   • If Estop is pressed have to re-home
   • Use LinuxCNC post-processor
   • Power Off Controller Before Computer

Basic Maintenance

Quirks

Conversion was a project.

Workpiece Examples

Supplemental Resources

Brandon's Notes

He does not make good notes.

Use the following settings in the Fusion 360 postprocessor (after selecting the emc2 linuxcnc post):

  • Safe Retracts and Home Positioning
    • Safe Retracts: G28

Try to use G54 instead of G53 because it's less scary.

FlatCAM Parameters

There are three different types of operations that go into CNC milling a PCB: hole drilling, trace isolation, and edge milling. Each of these operations will get its own section under this guide.

Hole Drilling

Hole drilling is accomplished with the variety of 1/8" shank jobber drills provided next to the CNC. The following equation is used to calculate the length that the drill needs to be passed into the PCB in order to clear a hole: . A tabular version is provided below for each 0.1mm increment:

Drill Diameter Depth
0.6 1.77
0.7 1.79
0.8 1.82
0.9 1.84
1.0 1.86
1.1 1.88
1.2 1.90
1.3 1.92
1.4 1.94
1.5 1.96
1.6 1.98
1.7 2.00
1.8 2.02
1.9 2.04
2.0 2.06

The following parameters apply for drilling operations. Note that the following machine settings may need to be changed for larger jobber drills: Feedrate Z, Spindle Speed.

Parameter Value
Diameter {Auto-filled from the DXF file import}
Cut Z {Use the provided look-up table above}
Multi-Depth
Travel Z 2
Feedrate Z 300
Spindle Speed 7200
Dwell
Offset Z 0

Trace Isolation

The tool parameters should be stored in the tool database which is loaded by default when you open FlatCAM. This section exists in case those parameters were somehow erased.

The main parameters for the v-cutter are specified when purchasing the cutter. The main ones at the makerspace are specified at 0.1mm tip, 20 degree v-angle.

The following table contains the milling parameters for the V-cutter.

Parameter Value
Shape V
V-Dia 0.1440
V-Angle 20
Tool Type Finish
Tool Offset Path
Custom Offset 0
Cut Z -0.15
MultiDepth
DPP 0
Travel Z 2
ExtraCut
E-Cut Length 0.1
Feedrate X-Y 240
Feedrate Z 60
FR Rapids 1500
Spindle Speed 12000
Dwell
Dwelltime 1

The tool library settin⬜gs for the cutter's isolation parameters are unchanged because it is assumed that the passes and overlap are going to be decided on the isolation tool panel instead of from the tool library.

There are two parameters for isolation milling:

Parameter Value
Passes {Determined on a case-by-case basis}
Overlap 20% {Determined on a case-by-case basis}

The determination for number of passes should be based on the minimum passes to ensure trace-to-trace clearance. This is largely determined by the maximum trace clearance on the PCB. Careful design and the generous use of copper fills is recommended since flatcam is not the friendliest software for non copper clearing. The following example should determine your minimum passes to be five by counting from the innermost pass to the outermost pass:

Flatcam screenshot.png

The determination for overlap should be based on the clearing of copper from the board. A generated CNC job could leave large uncleared islands like the image below. A smaller overlap percentage could generate a CNC job with fewer missed islands of copper that would make following PCB production steps harder.

Flatcam islands.png

Edge Milling

Edge milling is performed with the 1.5mm burr. These are inexpensive carbide burrs originally intended for use with fiberglass, but they can be used with the PF material preferred by the makerspace.

Manually entering parameters for edge milling is important because the software likes to crash if a tool is deleted from the tool table when performing edge milling. The following parameters should be entered instead of imported from the tool library:

Parameter Value
Dia 1.5
Cut Z -1.65
Multi-Depth
Travel Z 2
Feedrate X-Y 200
Feedrate Z 72
Spindle Speed 7200
Dwell