Homebrew PCBs

It's nice to hear someone air the dirty laundry. People usually don't talk
much about what didn't work. I've been pretty leary about the isolation
milling route (pun intended) so I tried the toner transfer method yesterday.
I was not impressed with that either. Granted, I used regular laser paper
but the results were so bad I didn't have much confidence in better paper
either. The toner appeared to cover well but came off way too easy. If I
have to iron for 15 minutes and maybe make multiple attempts it's just not
worth the trouble. I'm not that broke. So I bought a bottle of spray-on
negative resist and a can of developer, about $15 together. I've used it
before and it's a piece of cake, works perfect every time. If I use the mill
for drilling only I can avoid most of those Z axis problems as well, and
maybe keep the time consumed down to a level where it is worth the trouble.
There is some point at which it is actually more cost-effective to pay for
prototypes.
--
Phil Mattison
http://www.ohmikron.com/
Motors::Drivers::Controllers::Software

----- Original Message -----
From: lcdpublishing <lcdpublishing@...>
To: <Homebrew_PCBs@yahoogroups.com>
Sent: Sunday, December 31, 2006 1:51 PM
Subject: [Homebrew_PCBs] First efforts with isolation milling and the new
machine....


> Well, I can't say as I am thrilled or dissappointed.  I tried running
> a small PCB with fairly large traces.  There are a number of problems
> that I will need to resolve before expecting a good PCB from the
> machine.
>
> 1) I have to fix the problem with the Z axis saddle - this is
> something one of the newer list members has been helping me with
> (Ron), but I screwed up my end of the fix so I was running the test on
> the old hardware.  This is a mechanical problem that creates some
> inaccuracy in positioning in the Z axis.  With a samll 'V' cutter, you
> don't have much room for variations before your trace gets milled away.
>
> 2) A glitch somewhere caused the machine to lose position in X axis by
> about .200". This didn't happen on the first attempt, but did on the
> second attempt.  Not sure at all what the cause was or could be so
> this one will be a long term bug hunt I think.
>
> As one would expect from cutting copper with a V shaped tool, the cuts
> are not the greatest.  Copper itself is not the best machining metal.
> Couple that with the reality that the cutting SFM is so low because of
> the small cutter diameter.  The most RPM I can currently get out of
> the machine is only 7500 RPM, ideally it should be running at 100K or
> even faster but that can't happen till I can figure out a new spindle
> and afford some new hardware to do it.
>
> The traces that were not mucked up, were a tad smaller than they
> should have been.  They should have been .020" width but as best as I
> can measure it, they appear to be .012" wide.  I am using a small
> adapter chuck that is normally used as a quick change chuck for Dremel
> type tools. Having a few thousandths run-out on that is expected so I
> am not too concerned yet.
>
> The cutter I have is a V cutter, 60 degrees "D" shaped or in other
> words a 1/2 round tool bit (or another way of putting it is a single
> flute cutter).  It is solid carbide and seems to have held up good
> during these cuts so far.
>
> Had the X axis not lost position on the second attempt, I would
> probably have a good PCB to continue onto the second side machining.
>
> Also not overly thrilled with the Gerber tranlation software I have.
> It's a trial version so I can't really complain till I learn a bit
> more about it.  The isolation milling seems to work well, but I can't
> figure out what it needs/wants for the drilling operations. Luckily,
> that is pretty easy to program manually so if I can't get that to
> work, it still may be okay.
>
> I can see I will have to get going on the closed loop concept of the
> software and hardware.  Even though I am running stepper motors, I do
> plan to have a "near closed loop" operation at some point along the
> way.
>
> As for the speed of the process, I can see where it will be slow.
> However, I cannot yet determine how much longer it will take to do a
> PCB using isolation milling versus etching.  A higher speed spindle
> would certainly reduce the machining time so that is a primary
> drawback with my machine at present.
>
> But, looking at what is involved, it may not be much slower overall if
> you have a good spindle.  By comparison, the layout software I use can
> be used to print the layout for toner transfer then etching, or it can
> output the gerber files.  The translation software I am playing with
> takes about 1~2 minutes to translate the gerber into G-Code.  Once I
> have that, I load the G-code into the machine, set the origin on the
> workpiece and can (once I fix a few problems) hit start and let it
> run.  Once the first side is done, flip it over, re-set the origin,
> and let it run the second side.  Using stops on the table will reduce
> the amount of time there.  The machine has a 38 tool, automatic tool
> changer so once it get's going, there isn't much to do except watch it
> do the work.  It will do the isolation milling, drill the holes, and
> then mill the second side (although that requires manual intervention
> to flip the part).
>
> Compared to etching, I would eliminate the toner transfer which is
> mostly "Hit" for me rather than "Miss" so that doesn't take too long.
> Still have to print the layout, cut away the excess, align the two
> sides, transfer it, soak off the paper, scrub off the residue, touch
> up any spots that are not good.  Then it's into the etchant for about
> 20 ~ 30 minutes (it's cold in the shop so it etches pretty slow this
> time of year).  Once done there, it's manual drilling.  That goes
> pretty fast for me, but it is SOOOOOOOOOOO boring to me that the CNC
> machine is a welcome sight just for that alone.
>
> So, that's my first attempts at isolation milling.  I have to fix some
> software and hardware bugs before I can really do much else with the
> machine.
>
> Chris
>
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