My mini-mill CNC conversion is just about done (wow, been saying that for a long time). I would like to be able to use it for milling the copper on PCBs. The maximum RPM is 2000. Is that sufficient? If not, then my next project will be a mini-mini mill stand for my dremel.

Thanks

Hi Cactus,

Do ya like coffee? Because you'll have time for plenty of it with a 2000 rpm spindle :D

You will definitely want something much faster, especially for small cutters. You want light feeds and high speeds, to try to minimize burr buildup and tool clogging.

I did some PCB boards using a 1/4HP trim router and If I remember at a feed rate of 4-8 IPM.

Okay, now to Plan B: I'll make a new mount that holds a trim router and bolts to the mill's head. I guess if I'm really lucky, I'll find a low profile model that I can trim down even further. It's not like I'll need much Z movement :)

Thanks for the replies. I had no idea what kind of RPMs I would need.

My machine cutting copper of PCB spindle speed range 10000-30000 RPM.

You can see some PCB examples at my web.

www.geocities.com/cnc_designer/pcb.html

Cutting quality and feedrate proportional by the spindle speed.

bunalmis:

That is impressive work. What tool do you use to cut your pcb's?
What does your PCB3 (with the TI TMS320 chip) do?

robotic regards,

Tom

I made own cutting tool from 3 mm drill bits.
I give approx. 0.2 mm D form.

PCB3 controller board of my cnc.

So this is calculate the Step motor currents (microstep),
doing lineer interpolation and communicate with PC.

I have done some boards on my Taig mill. I have the spindle speed set to the fastest it will go. I cut this board at around 15 IMP. As you can see it came out nice. It matters on what kind of bit you have in it. Also did all the drilling too. It is very neat to watch it go!

bunalmis, woodknack:

how do you lay out your boards: by hand or software?

robotic regards,

Tom
= = = = =
"Because a man thinks with his dick,
a woman dicks with his thinking."

BY software. I have a friend that is right into it. He does them on some software. Ill ask him what he uses.

I draw by hand.

Can you please shed some light on the bits you guys are using for PCB milling. What should the end be like. Like an end mill, like a V or a round shape. If a V, then what should be the angle.

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

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

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.

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.