Spindle speeds for PCB milling

[routerman]

Real PCB drills (gerber, excellon) run 30000-60000 rpm on the drilling heads.

[hobbymat]

Yep,

Real drilling machines can go even faster, about 100k+ rpm, and they can drill a lot of holes in one second with the same spindle. Especially the small drills require an extremely high rpm.

The very good PCB mills made by LPKF use a 20k rpm spindle in their "cheap" entry-level models, and some more expensive ones use a variable-speed spindle for up to 60k rpm. Their most expensive model uses nowadays a 100k rpm spindle with ceramic bearings etc... I have to say from my own experience that the higher the rpm when milling the PCB, the better the result is. Try to use at least 20k rpm or whatever your Dremel-type tool can reach.

Good and cheap tools for PCB milling can be made of old/worn/broken PCB drills (tungsten carbide) that can possibly be had from a PCB manufacturing company quite cheaply or even for free. You'll need a diamond cutter for your Dremel to regrind the broken tip to a sharp V-shape. I dug out my supply of used 0.7 mm drills from the metal recycle bin of a local PCB house that shut its doors (...and also found three ballscrews, some PCB drill spindles and a a couple of small VFDs - now I've got the essential parts for my homebuilt CNC mill...

One more thing: the glass fibers in a normal FR-4 type PCB material wear down the sharp tools quite quickly - even if they are made of tungsten carbide. If you can use FR-3 (paper-reinforced epoxy) or FR-2 (phenolic resin and paper, a.k.a. Pertinax) materials, use them. They won't wear the cutters down so easily as they don't contain glass. And the milling dust in their case is not as heavily dangerous to inhale as the glass dust is. Use a good vacuum cleaner with decent filters in any case.


Happy PCBing,

Hobbie

[anoel]

Now, I milled my first PCB last week with my router. I'm using a Dremel Advantage as the spindle. And I used a 1/8" 60 degree single flute bit. I started out following the advice that I'vebeen reading regarding spindle RPM and was running the spindle at around 20k rpm starting out and milling at 15 ipm. The copper was a bit ragged on the edges of the tracks. So to see which direction that I needed to go in to make the edges smoother I sped the spindle up to max (30k I think) and that did not help. So I slowed the spindle down to the minimum (10k) and the tracks got much better. I sped the feed rate up to 130% (19.5 ipm) and it helped even more. I don't know if the heavier chip load is what smoothed things out or not but that's my suspect.

[sabodash]

Does anybody know typical way to produce G-code or DFX for milling from original layout file? I want use regular layout tool rather than draw milling pattern by hand.