Homebrew PCBs

Hi Stephen,

I'll answer your questions from the Electronics 101 thread:

ST wrote:

>Yes, i have read rotating the electrode is good for edm.
>I don't fully understand electrode erosion of different materials
>tho.
>Rigging a pump would not be a problem, i'm quite used to that sort of
>thing with a watercooled PC by now..


I used a combo dielectric duct and return ring around the electrode on
a EDM machine based on an HP plotter.  The idea was to use gravity
feed of distilled water ( the dielectric ) through a copper pipe
around the elctrode which also provided the pulse return path.  The
system had a spring to keep the duct in contact with the PCB and
attached plastic rod to provide capacitive feedback for depth.  My
hope was to speed up cutting the board by leaving a groundplane
however the drag of the duct slowed things down too much.



ST wrote:

>I would like to PC control it like a normal cnc drill.

You could do that with the A3967SLb s on a driver board and control
software on a PC.  Maybe EMC?

>How do you scan one line, at fixed speed or is it variable with
>current?

The gantry moves along the x axis in 0.001" increments.  The holding
torque of the steppers and the "stiction" of the acme threads holds
the gantry in place while the EDM head moves across the PCB and the
pulser removes 1 mil "dots" where there are no traces.  At the end of
the traverse the gantry advances another 0.001" and EDM head then
"etches" another line.  As I develop the system I'll probably follow
your suggestion and match the traverse speed to the pulse rate, but
for now -- Keep It Simple Stupid is the rule.

>You said you regulate height to have the right current? What happens
>if
>the electrode is "done" and is not moved, will it enlarge the cut or
>just stop because the gap is too large?


The gap ( height ) is regulated by measuring the gap breakdown voltage
as outlined in the power supply reference.  The EDM head is moved by a
stepper and the software puts out a pulse if copper is to be removed.
  At the end of the traverse the gantry is moved another 0.001" and
the  EDM head returns while cutting the next line. 


>I understand the going line be line, a fixed width thing. But i don't
>yet understand fully how you move along the line, or depth, and how
>you "lift" the cutting over the traces. Plase clarify again.

You don't lift the EDM head, you turn on the pulser and "burn" ( or
"etch" ) the away the copper you don't want.  The height or z axis
position of the electrode is controlled by the gap voltage.


>Also, i think making ground planes would ensure faster cutting of the
>overall board?

See my comments about the HP plotter.  Since you can raster scan any
image and output lines in the resolution of your choice you can move
in increments of that resolution along the x axis without having to
worry about the pulse return path.  


ST wrote:

>I would really like making boards that way, i think.
>what do you think the resolution would be?

If I could grind a fine enough point on the electrode my stepper and
leadscrew combo could "etch" 0.0001 inch dots ;D

Doing double sided boards with SMT is a pleasure since the number of
holes to be drilled is minimized.  You avoid all the mess and hassle
of TT.  No board scubbing.  No etching ( or mist or titrating ). No
paper residue.  Fine line widths and best of all minimal hole
drilling!!!

Curt

Hi Curt,

So the raster is scanned dot by dot no matter if cutting is needed, and  
with no regard to if the cutting is finished?
That is a good KISS approach, and if you go slow enough there should not  
be problems.
However in the future there would be speedup potential.
Also, i didn't mean to use the groundplanes for return, i thought when you  
have large copper areas you might just move over them fast and not need to  
scan it slowly if there is no cutting to be done.

I think the software should not be too hard to do, esp. if one uses a  
picture with the correct resolution already.

You know, if someone would find a good plotter pen or inkjet head i could  
even do the componet legend on this machine. Wouldn't it be great to do  
_all_ PCB work on the same machine? Now... a solderpaste dispenser and a  
pick and place head... okok i'll stop dreaming, those things are for later.

ST

On Wed, 29 Jun 2005 07:26:33 +0200, curt_rxr <cwrxr@...> wrote:

> Hi Stephen,
>
> I'll answer your questions from the Electronics 101 thread:
>
> ST wrote:
>
>> Yes, i have read rotating the electrode is good for edm.
>> I don't fully understand electrode erosion of different materials
>> tho.
>> Rigging a pump would not be a problem, i'm quite used to that sort of
>> thing with a watercooled PC by now..
>
>
> I used a combo dielectric duct and return ring around the electrode on
> a EDM machine based on an HP plotter.  The idea was to use gravity
> feed of distilled water ( the dielectric ) through a copper pipe
> around the elctrode which also provided the pulse return path.  The
> system had a spring to keep the duct in contact with the PCB and
> attached plastic rod to provide capacitive feedback for depth.  My
> hope was to speed up cutting the board by leaving a groundplane
> however the drag of the duct slowed things down too much.
>
>
>
> ST wrote:
>
>> I would like to PC control it like a normal cnc drill.
>
> You could do that with the A3967SLb s on a driver board and control
> software on a PC.  Maybe EMC?
>
>> How do you scan one line, at fixed speed or is it variable with
>> current?
>
> The gantry moves along the x axis in 0.001" increments.  The holding
> torque of the steppers and the "stiction" of the acme threads holds
> the gantry in place while the EDM head moves across the PCB and the
> pulser removes 1 mil "dots" where there are no traces.  At the end of
> the traverse the gantry advances another 0.001" and EDM head then
> "etches" another line.  As I develop the system I'll probably follow
> your suggestion and match the traverse speed to the pulse rate, but
> for now -- Keep It Simple Stupid is the rule.
>
>> You said you regulate height to have the right current? What happens
>> if
>> the electrode is "done" and is not moved, will it enlarge the cut or
>> just stop because the gap is too large?
>
>
> The gap ( height ) is regulated by measuring the gap breakdown voltage
> as outlined in the power supply reference.  The EDM head is moved by a
> stepper and the software puts out a pulse if copper is to be removed.
>   At the end of the traverse the gantry is moved another 0.001" and
> the  EDM head returns while cutting the next line.
>
>
>> I understand the going line be line, a fixed width thing. But i don't
>> yet understand fully how you move along the line, or depth, and how
>> you "lift" the cutting over the traces. Plase clarify again.
>
> You don't lift the EDM head, you turn on the pulser and "burn" ( or
> "etch" ) the away the copper you don't want.  The height or z axis
> position of the electrode is controlled by the gap voltage.
>
>
>> Also, i think making ground planes would ensure faster cutting of the
>> overall board?
>
> See my comments about the HP plotter.  Since you can raster scan any
> image and output lines in the resolution of your choice you can move
> in increments of that resolution along the x axis without having to
> worry about the pulse return path.
>
>
> ST wrote:
>
>> I would really like making boards that way, i think.
>> what do you think the resolution would be?
>
> If I could grind a fine enough point on the electrode my stepper and
> leadscrew combo could "etch" 0.0001 inch dots ;D
>
> Doing double sided boards with SMT is a pleasure since the number of
> holes to be drilled is minimized.  You avoid all the mess and hassle
> of TT.  No board scubbing.  No etching ( or mist or titrating ). No
> paper residue.  Fine line widths and best of all minimal hole
> drilling!!!
>
> Curt
>
>
>
>
> Be sure to visit the group home and check for new Links, Files, and  
> Photos:
> http://groups.yahoo.com/group/Homebrew_PCBs
>
> If Files or Photos are running short of space, post them here:
> http://groups.yahoo.com/group/Homebrew_PCBs_Archives/
> Yahoo! Groups Links
>
>
>
>
>

--- In Homebrew_PCBs@yahoogroups.com, "Stefan Trethan"
<stefan_trethan@g...> wrote:
> Hi Curt,
> 
> So the raster is scanned dot by dot no matter if cutting is needed,
> and   with no regard to if the cutting is finished?

Using 1 oz. copper board I can burn a 1 mil dot with one pulse and
finish an entire 8 x 11 inch board in under 45 minutes.


> That is a good KISS approach, and if you go slow enough there should
> not be problems.
> However in the future there would be speedup potential.


At this moment I'm just happy to have the basic setup working and
producing boards!  There will be time enough for refinement after I
get it debugged.


> Also, i didn't mean to use the groundplanes for return, i thought
when you  
> have large copper areas you might just move over them fast and not
need to  
> scan it slowly if there is no cutting to be done.
> 
> I think the software should not be too hard to do, esp. if one uses
a  
> picture with the correct resolution already.


I agree but right now I want to "crawl before I walk"  Right now I'm
working storing the results of a 1000 dot per inch black and white
scan in the controller.

News Flash!  Philips has just released the LPC2148 with 512kb memory
AND USB 2.0 compliance.  This should allow direct connection of a
scanner to the controller to download artwork from any source ( ie
magazines or books in addition to CAD files ).
 
> You know, if someone would find a good plotter pen or inkjet head i
could  
> even do the componet legend on this machine. Wouldn't it be great to
do  
> _all_ PCB work on the same machine? Now... a solderpaste dispenser
and a  
> pick and place head... okok i'll stop dreaming, those things are for
later.
> 


I worked on this with an HP 7550 using different sized "pens"
(electrodes).  As I noted elsewhere using vector graphics increases
the theoretical speed by reducing the amount of cutting but increases
the software load needed to insure a pulse return path.  Using raster
graphics just works.  Good enough for a first prototype.

I was thinking of using a tapered tube with needle in it's center to
dispense solder paste ( or One Shot Sign Painters enamel? ) in
controllable amounts.  Maybe later ;D


My next focus will be combining the electrode and a drill on a single
spindle to allow etching and dust free drilling in one setup.


Stephen, I'll try to get pictures and DWGs of the mechanical setup up
on the net after the July the 4th holiday, but I think your machine
should work just fine as a base for EDM.

Curt

> Using 1 oz. copper board I can burn a 1 mil dot with one pulse and
> finish an entire 8 x 11 inch board in under 45 minutes.
>

I see.

Just this minute i did a small experiment. I built the very simple supply  
shown in the link you gave for light edm work.
Connected it up and used a manually moved pointy steel screw as electrode.

i can definitely see that work is all i have to say. With this you could  
draw your PCBs by hand. Of course i got mighty rough edges with moving the  
electrode by hand, but i could mill slots in the copper with no problems.  
I kind of feared it might mill away all copper around tiny residual  
particles, so that they remain there, but it seems it cleans the copper  
clear off in neat circles.
I'm pretty much convinced it will work for me in a cnc setup.
I can even see it useful as a "electric milling wand" to do touchup work  
or cutting sripboard or even manually cutting very simple boards. It is  
much faster and cleaner than scratching, as it doesn't affect the epoxy.  
The water is a drawback though.
Very rewarding experiment, recommended for everyone.

(Here the URL again:  
<http://cscott.net/Projects/FabClass/final/edesign1.html#schematic> "A  
simple circuit", stay under 30V if you want to touch the eletrode.).



>
>
> At this moment I'm just happy to have the basic setup working and
> producing boards!  There will be time enough for refinement after I
> get it debugged.

I really need to see pictures. pleeeaaasssee ;-)


>
>
> I agree but right now I want to "crawl before I walk"  Right now I'm
> working storing the results of a 1000 dot per inch black and white
> scan in the controller.
>

Yea that are only small details, the mechanic/electric setup works, and  
that is great.
How the software is done is a minor point. Of course milling isolation  
paths directly would be faster than raster but time isn't really an issue  
at the moment.
Also, the software is easily tinkered with later on.

> I was thinking of using a tapered tube with needle in it's center to
> dispense solder paste ( or One Shot Sign Painters enamel? ) in
> controllable amounts.  Maybe later ;D
>

I thought about a paste syringe with pneumatic dispenser. But later is the  
right word.

ST

Hi guys,
 
I´m very interested in building one of these Power Supplies too, but I
have problems
in finding the parts listed in the drawings from Scott.
 
http://www.elfa.se/elfa-bin/dyndok.pl?dok=5014.htm
 
These are the ones I can get locally, cant you tell me what part no’s I
can use to
substitute the 16A and 60A IRG4’s.
 
Does anyone have info on the 100uH coils how these are winded?
 
Stefan, any clue on how big transformer we will need for this? You also
use 240V as I do?
Is there any mods that can be done to get it working with 240V / 50Hz
 
 
Cheers
Bengt
 


[Non-text portions of this message have been removed]

--- In Homebrew_PCBs@yahoogroups.com, "Stefan Trethan"
<stefan_trethan@g...> wrote:

Hi Stefan ( sorry about misspelling your name before -- must be brain
fade induced by the summer heat ),


 
> Just this minute i did a small experiment. I built the very simple
supply  
> shown in the link you gave for light edm work.
> Connected it up and used a manually moved pointy steel screw as
electrode.
> 
> i can definitely see that work is all i have to say. With this you
could  
> draw your PCBs by hand. Of course i got mighty rough edges with
moving the  
> electrode by hand, but i could mill slots in the copper with no
problems.

The higher pulse rate and lower current power supply yields a MUCH
smoother cut.

  
> I kind of feared it might mill away all copper around tiny residual
 
> particles, so that they remain there, but it seems it cleans the
copper  
> clear off in neat circles.
> I'm pretty much convinced it will work for me in a cnc setup.
> I can even see it useful as a "electric milling wand" to do touchup
work  
> or cutting sripboard or even manually cutting very simple boards. It
is  
> much faster and cleaner than scratching, as it doesn't affect the
epoxy.  
> The water is a drawback though.


In what way?  It keeps the elctrode from burning and washes out the
particles.  

> Very rewarding experiment, recommended for everyone.
> 
> (Here the URL again:  
> <http://cscott.net/Projects/FabClass/final/edesign1.html#schematic>
"A  
> simple circuit", stay under 30V if you want to touch the eletrode.).
> 
>
> I really need to see pictures. pleeeaaasssee ;-)
> 
>


I'll get right on it after the 4th.  Promise ;D


Curt

--- In Homebrew_PCBs@yahoogroups.com, Bengt Sjölund <bengt@t...> wrote:
> Hi guys,
>  
> I´m very interested in building one of these Power Supplies too, but I
> have problems
> in finding the parts listed in the drawings from Scott.
>  
> http://www.elfa.se/elfa-bin/dyndok.pl?dok=5014.htm
>  
> These are the ones I can get locally, cant you tell me what part no's I
> can use to
> substitute the 16A and 60A IRG4's.
>  
> Does anyone have info on the 100uH coils how these are winded?
>  
> Stefan, any clue on how big transformer we will need for this? You also
> use 240V as I do?
> Is there any mods that can be done to get it working with 240V / 50Hz
>  
>  
> Cheers
> Bengt
>  


Hi Bengt,

I ordered most of the parts from Digikey without problems.

I used a surplus 18 volt 2 amp transformer I had on hand and wound 12
guage magnet wire around surplus 2 inch toroids until I measured 100
microHenrys on my LCR meter.

For a 240 volt line you could probably use a full wave rectifier
instead of a bridge rectifier.

If the IGBT s are hard to find in the EU you could use Mosfets and
reconfigure the drivers.  Probably be cheaper anyway....

HTH

Curt

On Thu, 30 Jun 2005 05:31:22 +0200, curt_rxr <cwrxr@...> wrote:

>> water is a drawback tho.
>
> In what way?  It keeps the elctrode from burning and washes out the
> particles.

That was meant for using it "freehand" to do board touchup or cutting of  
stripboard.
'course it's required, but if it worked in air just as well i would prefer  
;-)
ST