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- Jog the head to a spare area on the copper clad and gently lower the head with your hand onto the copper clad.
- Make sure both the tip of the end mill and the foot of the head are on the copper clad.
- If the end mill touches the top of the copper clad before the head bottoms out, adjust the limit screw so that the head bottoms out before the end mill touches the top of the copper clad.
- Spin up the drill head from the Jog window interface.
- Toggle the "head down" to engage the endmill. The end mill should not be touching the top of the copper clad after the head goes down!
- Once the foot has struck the top of the copper clad, begin lowering the limit screw until the end mill engages the copper layer. The pressure from the machine should keep the drill head at the lowest position allowed by the limit screw.
- Once the end mill engages the copper you can jog the end mill around in a single direction with the arrow keys on the keyboard. NEVER engage copper clad or jog the end mill across the copper clad without the head being spun up. This will immediately and permanently break the end mill. They are very expensive...don't break them...please!
- With the end mill engaged and a small jog in an arbitrary direction, you want to continue to lower the limit and jog the end mill a little until you can see the black/brown backing underneath the layer of copper.
- Adjust the limit screw 3-4 clicks down (that is to say lower the end mill just a smidge more). This is because the copper clad is not always perfectly flat and the section you chose to test may be just a bit lower than other sections, if that is the case and you do not lower it just a smidge more you may end up with sections where the copper is not completely milled away.
Speed and Feed Rates
In order for the end mill to properly cut through the copper layer of the board the machine needs to know how fast (think inches in a the X direction per second) to move the end mill.
If the end mill is moving too quickly then the copper may appear "torn off" instead of cleanly milled away. This could lead to inadvertent shorts through the isolation layer between traces. It will also require considerably more effort to clean up after you are done milling the board.
The primary factor that effects the mill feed rate is the thickness of the copper that is on the copper clad. A thicker copper layer will provide lower resistance to an electrical resistance, but will take slightly longer to mill through (aka the feed rate needs to be slower).
The following feed rate table is a good starting point for settings, however you may need to adjust the values depending on how deeply you mill into the FR4. Always perform test mills and feel the edges of the cuts that the mill makes in order to judge for yourself if the feed rate is too fast.
| Note |
|---|
No harm can come from setting the feed rate too slowly (it'll just take a little longer), but you can permanently damage the machine, end mill, and PCB board if the feed is to HIGH. |
Completions
De-burring
Cleaning
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Ultrasonic cleaners (such as the one in the machine shop) can be used for this purpose, but care must be taken that the bowl does not have random metal shavings or dust that have collected from cleaning machined items. These particulate may embed themselves in the isolation between traces and cause shorts. Always rinse the board after cleaning with the ultrasonic cleaner, failure to do so will result in a sticky mess and impossible soldering. This is because the cleaner uses a solution of water and industrial detergent, the detergent will leave a thin film behind that is intended to be rinsed away. Do not forget this step!
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Inspecting For Shorts
Due to the imperfect nature of the PCB milling machine, once a board is finished milling and drilling there can often times be little bits of copper
Tools you will need:
- Stereo Microscope
- Digital Multimeter (DMM)
- Xacto Knife
- Dental Picks
- Patience
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