Genmitsu Milling¶
I want to have a place to corral all my learnings about my Genmitsu. Lots os AI assisted Learning here.
Feeds and Speeds – Amalia and Angel Edited for Genmitsu
Speeds & Feeds for Milling Machine Tools
| Tool Size | Spindle Speed (RPM) | Feed Rate (mm/min) | Plunge Rate (mm/min) | Cut Depth per Pass (mm) |
|---|---|---|---|---|
| 1/64" (0.0156") End Mill | 10,000 - 12,000 | 100 - 200 | 50 - 100 | 0.1 |
| 1/32" (0.0313") End Mill | 10,000 - 12,000 | 200 - 300 | 75 - 150 | 0.2 |
| 1/16" (0.0625") End Mill | 10,000 - 12,000 | 300 - 400 | 100 - 200 | 0.3 |
| Engraving Bit (V-bit, 30° or 60°) | 10,000 - 12,000 | 80 - 150 | 40 - 80 | 0.05 - 0.1 |
1/64”: Best for fine trace isolation and small detailed cuts. Requires a shallow cut depth to avoid breaking.
1/32”: Common for trace isolation and small routing features. Deeper cuts possible.
1/16”: Best for board cutouts and large clearances.
Engraving Bit: Ideal for fine detail work. cut depth varies depending on the desired isolation width.
Runout¶
Runout is how much a spinning tool wobbles off-center as it rotates. Instead of spinning perfectly true, the tip traces a small circle rather than a single point. Even 0.1mm of runout on a PCB engraving bit makes a big difference in trace width and cut quality.
How to test for it:
Sharpie method:
- Chuck up a bit
- Hold a sharpie or pen steady against the shank while slowly spinning by hand
- If it marks all the way around evenly — good
- If it only marks one side — you have runout
Visual method:
- Turn the spindle on at low speed
- Look at the bit from the side
- A bit with bad runout will look blurry or like it's wobbling
- A true bit looks like a single sharp line
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Try uploading a video of the bit spinning to Gemini and see if it can analyze it
Line Depth¶
Line Depth Your copper layer is only about 0.035mm (~0.0014") thick. You only need to cut through that. Every extra thou of depth just widens the cut and removes more material than needed.
The Test starting at 0.001" and stepping up to 0.020". Each step is labeled so you can see the result.
What running it tells you:
Too shallow (0.001"–0.003") — the bit barely scratches the copper, traces may be incomplete or connected where they shouldn't be Sweet spot (around 0.004"–0.008") — clean isolation, copper fully removed between traces, edges look sharp Too deep (0.010"+) — traces get wider than designed, you start cutting into the FR1 substrate, and fine traces may disappear entirely
The practical takeaway: Look at the test results and find the shallowest depth that gives you clean, fully isolated traces — that's your ideal depth of cut setting for that bit on that machine.
HOW THIS WORKS: When Mods converts the image to a toolpath, it reads the pixel width of each line. A thicker white line in the image = more material to remove = the bit has to cut wider. A thinner line = less material = narrower cut.
That's how one image creates different effective cut depths — the varying line widths in the image force the V-bit to different depths automatically.
Key insight — with a V-bit or engraving bit, width and depth are the same thing. The tip is a point. The deeper it goes, the wider the cut it makes because of the angle of the V shape.
bit needs to cut wide → bit must go deeper to achieve that width A narrow line in the image → bit only needs to cut narrow → bit stays shallower