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