Re: CNC Milling PCB's

Hi everyone,
I guess I've actually have machined PCB's, so I'll share what I know.

Software wise, I've drawn my circuit in AutoCAD, and then converted it to
g-code. Probably not the prettiest circuit boards, lots of square boxes,
etc, but much more efficient in terms of the max number of lines that you
have to cut on the CNC. Just a real pain to draw out.

I first tried milling with regular endmills, carbide, 2 flutes, 1/16" dia.
with my main spindle. Unfortunately, my spindle has a top speed of about
3000 rpm, which is pretty slow for such a small bit. The 1/16" endmill
worked, but after a few inches of cutting, it started to leave a ragged
edge. (it was brand new) The fiberglass substrate is pretty abrasive.

Next, I machined up a holder to clamp my Dremel on to the side of the head
on my mill. Cranked the Dremel up to full speed, and started milling. The
1/16" end mill worked great, leaving a clean edge. But unfortunately,
being 0.0625" wide, didn't leave much metal on the board, especially with a
0.1" spacing between IC pins. I next tried an 1/32" carbide endmill, but
again, the surface finish wasn't the greatest. (need more speed than my
Dremel could put out)

A friend of mine mentioned used PCB bits at the local surplus store. Small
1/8" shank bits, with little plastic disks around them. Picked up a few.
These bits seem to come in 4 different varieties:

End mills - flutes look like regular end mills,

Fish Tail end mills - looks like a regular end mill but the bottom instead
of being flat, ends in a fish tail, the flutes criss-cross to form a
diamond shape.

Drills - looks like drill bits, usually have a drill number printed on the
pastic disk. Good for drilling thru holes.

Rasp - looks like a miniture round hand rasp, with a little triangular
spade on the bottom. This is the ones I use to mill the traces with, 1.5mm
size seems to work well.


Of all the bits that I tried, the rasp gives the best surface finish. I
only go about 5 thou deep to cut the trace, so only the triangular portion
is cutting the copper. Of course, with such a shallow cut, you have to
make sure that the board is absolutely flat. They usually are, but to make
sure, I double side tape them to a piece of MDF, which is then clamped to
the mill table. (also allows me to drill the holes without reclamping) If
I have any clamping pressure on the PCB, it bows up in the middle.

Anyways, I finally get everything working, (gone thru a pile of PCB's and
many many fustrating hours, days, weeks....) and the motor on my Dremel
burns out. What do you mean you can't run a Dremel 2 hours straight! My
final configuration, I use a cheap Makita laminate trimmer (a couple of
holes drilled into the casing to keep it cool) that I picked up for $39,
running at 12,000 rpm, made a small adapter to get the 1/4" collet down to
1/8" bits that I'm using.

Hope this helps,
Vincent.

PS. the bits are also available in Canada at:

Princess Auto: http://www.princessauto.com/
Lee Vally tools: http://www.leevalley.com/home/main.asp
In Toronto: Active surplus on Queen St. East, 3 or 4 bits for a buck

>Ian England wrote:
>--- In CAD_CAM_EDM_DRO@y..., captnorm3@j... wrote:
>> i am very interested in what you are doing , i to want to make some
>> circuit boards for my own use in electronic projects using the
>> routing method, i would like to get away from chemical etching
>> i do have a question on routing PCB how narrow can the cuts be
>> made also how narrow can the runs be made ?
>>
>
>Hi
>
>I have not actually machined a board yet, still got to fix up a high
>speed spindle of some kind. When I get there I will experiment and
>post the information. I think it might well depend on the machine and
>spindle you use.
>