Archive of the former Yahoo!Groups mailing list: Homebrew PCBs

For what it's worth...

I have plenty of CNC experience - both industrial and hobbiest, been
working with industrial CNC machines since the 70s and worked as an
Engineer for a machine tool company for 6 years and wrote plenty of
software to help people with their CNC machines.

My hobbiest CNC machine is a CNC router that is going through a lot
of changes and tests. The purpose of the machine is too make parts,
but it is also doing double duty as a test bed for a whole host of
ideas and concepts.

The machine has 38" x 22" x 6" (X Y Z) travels
Driven by 160 Oz-in stepper motors & .2" pitch ball screws
Stepper driver is a HobbyCNC chopper driver
Software is MACH3 from www.ArtofCNC.CA


I have used four different spindles on the machine so far.
1) Porter cable trim router
2) DeWalt, 1 1/2 HP variable speed router
3) Bosch, 1 1/2 HP Variable speed router with quick change adapter
4) At present, Shop made spindle, driven by a DC treadmill motor
which is driven by a www.beel.ca motor control and is controlled
completely through software. This spindle also incorporates a quick
change collet system.


While I certainly don't have electronics experience, I can offer
advice based on practical experiences with CNC should the group like
to have my advice.

I do plan on getting into circuit board milling and drilling so that
I can learn that process, so there is an active interest on my part
as well.

Prior to starting the build or even mechanical design of the machine
there are a couple of things you should consider first as they will
control a lot of the designs deeper into the machine.

1) Controlling software - I highly recommend MACH2 software from
www.artofcnc.ca - great product, very large amount of features and
overall, just a very capable CNC control software package - I have
yet to find anything close to being as good. Price $150.00
registered, free to try and use (with very minimal restrictions).


2) Spindle. I believe that drilling the circuit board material is
pretty abrasive on tooling (fiber glass usually is). From the
little electonics experience I have so far, it also appears as
though there are some pretty small diamter holes that need
drilling. Small drills will require high-spindle speeds AND a
spindle with minimal run-out - cheap rotary grinders may not be the
best solution, but probably would work.

For milling, I am not sure of what people do in this regard on
circuit boards. There are two approaches that I have seen...

A) - flat bottom endmill cutter, and mill away all (or most of) the
copper from the circuit board, similar to what a chemical etch would
do.

B) - 'V' bottom endmill cutter which is used to mill a "V-Groove"
around each of the traces, thus only cutting away enough material to
isolate each trace.

Method A might a require a slightly more rigid spindle than method
B, but I don't think it will matter much either way.

3) Overall cost of the machine. If making it cheap is the primary
concern, then everyone must accept the pitfalls of a "Cheap"
machine. My personal preference is to go with a more robust design
that may cost a tad more, but atleast the machine can do what we
want it to do.

4) Travels of the 3 axis of motion, X Y & Z. Z is the up and down
(drilling motion) axis. X is left to right, and Y is in and out.
What size circuit boards would you all expect to mill and/or drill
with the machine?



Chris