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Old May 27th 15, 12:29 PM posted to rec.radio.amateur.homebrew
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Default Milling of PCBs?

I wonder if anyone here has experience of milling PCBs using
CNC rather than etching them, and if so, what pitfalls and pratfalls
were encountered?




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Old May 27th 15, 03:38 PM posted to rec.radio.amateur.homebrew
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Default Milling of PCBs?

On Wed, 27 May 2015, gareth wrote:

I wonder if anyone here has experience of milling PCBs using
CNC rather than etching them, and if so, what pitfalls and pratfalls
were encountered?

No, but I have done boards at times using a Dremel tool and a cutting bit.
It worked better for discrete components than ICs, it being easier to
make larger "pads", and I'm not certain
just building over the circuit board is all that worse. You have to use a
light touch, press too hard and maybe you cut through the board, don't
press hard enough and you may not isolate the "pad" enough.

Obviously if you have a CNC, you can do much finer work. I don't really
see why subtracting via cutting is all that different from subtracting via
etching, though if making multiple boards, you make the layout and can
etch the boards at the same time, while with a CNC, you have to do one at
a time.

Michael
















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Old May 27th 15, 05:17 PM posted to rec.radio.amateur.homebrew
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Default Milling of PCBs?

On 5/27/2015 7:29 AM, gareth wrote:
I wonder if anyone here has experience of milling PCBs using
CNC rather than etching them, and if so, what pitfalls and pratfalls
were encountered?


Years ago a place I worked had one of the machines that cost a few
thousand. It wasn't great as they hadn't provided a good base so the
board could be inserted multiple times with the same registration or
easily flipped for double sided. The bits were conical rather than flat
tipped and tended to break easily. In the end the company went belly up
and we were stuck with proprietary software that was no longer
maintained. The only people who really used it much were the RF guys...


Some in s.e.d use a mounting technique of soldering bits of double sided
PCB onto a board of copper clad as soldering islands. No etching
needed. Not the greatest appearance, but it is very fast and simple to
make and you do have a decent ground plane even if you don't have good
impedance controlled runs... maybe. I expect you could find a wire with
the appropriate thickness insulation for a given impedance and glue it
to the copper clad. Think microstrip.

--

Rick
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Old May 27th 15, 07:20 PM posted to rec.radio.amateur.homebrew
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Default Milling of PCBs?

In article , rickman wrote:
On 5/27/2015 7:29 AM, gareth wrote:


I wonder if anyone here has experience of milling PCBs using
CNC rather than etching them, and if so, what pitfalls and pratfalls
were encountered?


Years ago a place I worked had one of the machines that cost a few
thousand. It wasn't great as they hadn't provided a good base so the
board could be inserted multiple times with the same registration or
easily flipped for double sided. The bits were conical rather than flat
tipped and tended to break easily. In the end the company went belly up
and we were stuck with proprietary software that was no longer
maintained. The only people who really used it much were the RF guys...


There are still fast-prototyping PCB milling machines which do this.
They don't seem to have a really big market - "quick turn" fabrication
houses are plentiful and are usually quick enough. In-house milling
seems to be mostly for "We've gotta have this *today*" applications,
or for the occasional situation where one is too afraid of having the
details of the PCB "leak" to a competitor before the product comes
out.

From what I've heard, one of the problems with this approach is that
milling the copper off of the PCB isn't a trivial problem. Copper is
soft and flexible enough that it can tend to clog the bit, or
stretch-and-tear rather than milling off of the substrate cleanly.

Some hobbyists do it with (e.g.) Zen CNC systems, or Dremel-based
CNCs, etc. I know there's software out there which can read in a
Gerber file, and produce a file of G-code commands which will mill out
an isolation zone around each trace or area plotted by the Gerber. As
with an etched PCB, you'd want to fill as much as possible of the
unused space with ground plane (or unconnected fill zones) so that you
don't end up having to mill away lots of copper.

Using carbide bits would (I think) be essential - high-speed steel
probably won't stand up to FR4 for very long.
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Old May 29th 15, 10:14 AM posted to rec.radio.amateur.homebrew
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Default Milling of PCBs?

On 27.5.2015 14:29, gareth wrote:
I wonder if anyone here has experience of milling PCBs using
CNC rather than etching them, and if so, what pitfalls and pratfalls
were encountered?


I have experimented some pcb milling, using desktop CNC with
working area slighly larger than A4-paper. Smallest SMD
components were 0603 size, using v-shaped engraving bits of
0.1mm tip diameter.

Needs two softwares, first one to design the pcb and second
phase is to convert this to cnc code. This takes some time
as the cutting procedures are adjustable to each line on pcb
desing.
The need to adjust hole sizes, viases, layers, line widths
depend on pcb, more complex designs take more time also
preparing time for cut and transfer to individual cutting
files with different tools used. Some re-design is needed
sometimes between pcb-design and cnc-prepare as cutting
width is constant.

This two-phase is one way to do all, some sw packages do
both phases internally and the pcb design is directly what
is actually cut, this may sometimes be less optimized for
cutting time spend.
So software selections need some evaluation depending
on the actual needs.

Third sw is needed to finally control the cnc-cut described
in the tool path files prepared in two previous phases.

Most difficulties are keeping pcb material exactly flat on
milling base plate, use of vacuum plates might benefit, but
this needs extra accessories like vacuum pump etc. so this
isn't choice for occasional use.

CNC machines are like cars, some of them have automatic tool
changers, some don't, some automation speeds much the
time spent on tool changing between cuts, though by
increased price level of the cnc-mill.

CNC is ok for prototyping or limited small amount of pcb's,
as pcb markings and specific solder layers are not simple to
add to milled plate.
Commercial processing is done using more sophisticated means
and machinery so all these comments don't apply to them.

To sum briefly, most of the time around 50..70% of time is
spent on describing pcb-files and preparing them to cnc code.
Actual cut is 10...20% of time used.


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Old November 16th 17, 05:32 PM posted to rec.radio.amateur.homebrew
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Default Resolving AM and FM if a very narrow Xtal filter

Ian Jackson wrote on 2/2/2014 3:46 PM:
On 5/27/2015 7:29 AM, gareth wrote:
I wonder if anyone here has experience of milling PCBs using
CNC rather than etching them, and if so, what pitfalls and pratfalls
were encountered?


Years ago a place I worked had one of the machines that cost a few
thousand. It wasn't great as they hadn't provided a good base so the board
could be inserted multiple times with the same registration or easily
flipped for double sided. The bits were conical rather than flat tipped and
tended to break easily. In the end the company went belly up and we were
stuck with proprietary software that was no longer maintained. The only
people who really used it much were the RF guys...


Yeah, a place I worked had one of these, likely the same company as theirs
went belly up too. RF guys use double sided often if not always. Digital
stuff often needs more layers.

The island breadboard approach is even more limited being effectively single
sided and entirely unsuitable for any type of high density packages. So
again, mostly used for RF type of designs.

--

Rick C

Viewed the eclipse at Wintercrest Farms,
on the centerline of totality since 1998


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