Homebrew PCBs

Joe,
Reading in the pcb-gcode group, I learned that 
you needed to "calibrate" your bit to find out 
exactly what size it was actually cutting based 
on depth of cut as not all bits are made 
equal.  I have a project coming up that will use 
Tssop14 footprint chips and the pin spacing is 
.65 mm with a pin width of .35 mm which leaves an 
isolation width of .3mm (~.012"). So I bought a 
pack of various sizes and started to play with 
width of cut vs depth of cut. I am trying to 
perfect my equipment to be able to RELIABLY cut a 
good isolation at a depth of .002". Still playing 
with that one. Just finished my vacuum chuck but 
have not tried it yet.  Was getting decent cuts 
using the double sided tape routine, but got 
tired of the sticky mess on the back of the board.

I have not noticed any particular smell to the 
cutting process, but there is always some risk 
with ANYTHING. I still think it is better than 
the risks with chemicals! (My personal opinion)

Art
Country Bubba


   At 10:37 AM 12/13/2012, you wrote:
>Hello Art,
>
>Thanks for your advice.
>
>How did you end up using the 30 degree V-bit? Have you tried the other
>v-bits such as 45, 60 and 90? I am trying to understand how you went about
>the process. Whether you bought all the v-bits and just tried them all to
>figure out which one was best or if you were recommended that particular
>v-bit by someone.
>
>About the CEM board, I read that it is easier on the drill and mill bits.
>But, I also read that it emits a weird smell when being cut. Did you notice
>something like that? BTW, do you know if the fumes from cutting the CEM
>boards are carcinogenic? I have been told this "there are a zillion
>carcinogenic phenolic compounds...pentachlorophenol for example." Just
>curious, if you gave this any thought.
>
>Thanks again,
>Joe
>
>
>
>On Thu, Dec 13, 2012 at 9:25 AM, Art Eckstein <
>art.eckstein@...> wrote:
>
> > **
> >
> >
> > Joe,
> > Yep, you have run into a couple of problems with
> > boards being level. It has been found the boards
> > will "bow" up in the middle when clamped on the
> > edges and FR$ has (I think) a 10% tolerance for
> > board thickness. The best way to hold down the board is by vacuum.
> >
> > As for the "paper" board, you want CEM type as
> > opposed to the FR4. I get mine from a seller on
> > Ebay
> > 
> (<http://stores.ebay.com/PCB-Laminates-Copper-Clad?_trksid=p2047675.l2563> >).
> > There are a few "autoleveling" packages that
> > probe the board height before doing the isolation
> > milling and these seem to work quite well. I use
> > Eagle and a ULP called pcb-gcode.ulp with autoleveling to make my boards.
> > For fine work, I use a 30° V bit, and for general
> > non critical stuff, a 60° one from <http://www.drewtronics.net/>.
> >
> > HTH
> > Art
> > Country Bubba
> >