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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