Homebrew PCBs

VERY COOL!  ;-) I am glad to hear that no goats were harmed in the 
production of those EDM cut PCBs :-)

Chris




--- In Homebrew_PCBs@yahoogroups.com, roger lucas <ralucas4277@...> 
wrote:
>
> 
> Well, I finally motivated myself this holiday weekend
> to get my PCB EDM lash-up to cut copper, and, YES, it
> does cut clean lines thru the copper without board
> burning or marking. Shine a torch through the tracks
> from the rear of the board and there is a faithful
> line of light, (no firstborn goats or pentagrams
> neccessary).
> 
> With my highest power lens and head magnifier I could
> see no trace of copper whiskers on the EDM'd track.
> Interestingly, the copper is blasted away entirely
> below the cross section of the wire, there is no
> 'erosion bleeding' into the surrounding copper outside
> of the wire dia.
> 
> Have only cut straight lines so far with 26 swg and
> with a 0.2 mm step increment, (need to modify the
> stepper gear ratio), and with multiple (continuous)
> sparking between increments, (no on/off sparks or
> raster yet).
> 
> One significant problem has emerged which Curt
> Richards did not address, (or if he did, he did not
> mention it). The wire electrode erosion is
> significant, and will require an active Z axis
> correction to maintain as consistent a spark gap
> distance as possible between the electrode and pcb
> surface. To do this I will insert a routine to 'touch
> down' the electrode on the copper to zero the gap,(no
> spark, closure sensed by two PIC output/inputs for
> voltage present), and then retreat the electrode to a
> standard clearance before any track eroding is
> commenced, (Andrew, this is why I need the BMP byte by
> byte transfer). This will also tend to compensate for
> any board distortion. 
> 
> Used tapwater as a dielectric with no problems, (the
> modified Garden of EDM circuit controls the
> electrolysis with no problems).
> 
> Curt controlled his spark discharge voltage by
> dynamically adjusting the electrode gap on the fly. I
> think that for pcb work this is not the correct
> approach because of the wire erosion problem, since
> one needs to KNOW the gap distance AND available
> discharge energy BEFORE discharge, which is why I am
> going for the touch down zeroing method, (slower but
> speed is not significant at the moment). The discharge
> energy will be set by presetting the voltage level
> required and capacitor selection, (simple comparator
> control integrated into the spark control). I think
> this is the secret of successful pcb edm'ing.
> 
> This is really looking as if direct raw copper board
> to finished pcb is going to be possible.
> 
> Roger
> 
> 
> 
> 		
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