Homebrew PCBs

--- ghidera2000 <ghidera2000@...> wrote:

> Could you expand on that? What kind of troubles did you have?

Sure. The bits bust, usually in the first 10 seconds of routing.
Milling copper, PCB or otherwise is tricky business.  It's very 
soft and bits tend to 'mush' through it rather than cut.  Even 
spinning the bit as fast as it will go, and slowing the feed rate 
to almost nothing doesn't help.  I'm guessing the ratio of
the thickness of copper to the size of the cutting face of the 
smaller sized bits just doesn't work.  A possible solution is to 
go to thinner copper like 1/2 or 1/4 oz, but I don't have any 
stock of that on hand.


> A tiny bit of a warp in the board can cause over or undercutting 
> with a V-bit. 

Another problem with V-bits is if you set them deep enough to 
remove a lot of material, it removes a lot of underlying substrate.
I gave up on 'em pretty early on in the process, and use endmills
for everything.  One of the techniques in the quickcircuit user
guide is to do all your routing with the V-bit initially (fast),
which removes most of the copper, then following it up with an 
endmill.  I'm not sure if this really saves any time, what I 
usually do is get it running and let it go, checking on it 
periodically.  A complex board can take several hours per bit 
to run, but since it's unattended it kinda doesn't matter.


> The endmill is appealing in that trace width doesn't vary with 
> depth.

Yes.  I usually route with 2, sometimes three sizes.  A large-ish
bit like 20 mils to do the brunt of the isolation, 12 mils for 
whatever features the 20 can't cut, and 50 mil if I have a lot
of copper to remove.  In my application I do a lot of microwave 
striplines and the quickcircuit has pretty good repeatability
and accuracy.  The downside is you don't want to bust too many
bits in the process, or your costs go up quickly.  Once I got
used to using it, then creating the right drill and route layers
in my layout software to accomodate it, I can make some pretty
nice double side boards with only one flip of the material and
a couple bit changes, and even create routed snap-off panel edges 
for our productions' automated assembly.  The quickcircuit is a 
nice tool but it's expensive to buy and finicky to operate, so 
I've ruled one out for my home business PCB jobs.  Toner transfer
is a bit more practical for most stuff I do.

Mark B.
Albuquerque, NM