Homebrew PCBs

Richard Mcfarlane wrote:

>Hi Curt,
>I like to see more about your CNC- EDM experiments.
>I carefully observed THE GARDEN OF EDM - PWM power
>supply is much better than the crude old RC-Generator.
>For efficiency reasons I have to sacrifice about IGBT
>costs.
>I wish to learn from you about the UP/DOWM motor
>control quill movement to maintain the constant gap
>voltage across the tool electrode.
>Presently I am experimenting with an Opto-Electronic
>comparater design to control the arc voltage (Based on
>a Japanese Patent).
>
>Regards.
>Richard
>
>  
>
Hi Richard,

Sorry about the delay in my PCB EDM work but I've been rebuilding a 1954 
Willys Pickup!   The town I live in does not like unlicensed vehicles on 
private property ( might be a REDNECK in town   :-)    gotta' protect 
property values   >:o    ).  I've been hip deep in truck parts for the 
last few months.  I've only been able to do a small amount of work on 
the PCB EDM project, but I've summarized it below.

I'm working on reconfiguring the Garden of EDM to the International 
Rectifiers  IPS5451 "intelligent power switch" instead of IGBTs or 
FETs.  The IPS5451 chips have a 50 volt and 45 amp pulse limit. and 
built in thermal and over current protection.  I'm using a 556 dual 
timer to control the pulse repetition rate and gap breakdown voltage.  
The 555 allows pulse rates up to the 1 mHz  range and the 30 amp rating 
of the IPS is about twice the needed pulse current.  I would like a 
higher voltage rating, but my initial experiments show clean traces with 
.003 inch brass wire as the electrode with pulse rates of 30,000 per 
second.  Since the IPS handles all the proteection circuitry internally 
( the chips are meant for automotive uses ) the Garden of EDM circuit is 
reduced to a complexity level that matches the RC EDM circuitry. 

My breadboarded circuit consists of  a 48 volt DC-DC converter ( too 
close to the IPS limits, but it's what I've got at hand ) feeding a   
~10-20 uf polypropylene cap with a SCR triggering the pulse when the IPS 
has switched off.  One half of the 556 controls the discharge rate and 
the other half blocks the IPS while the gap is conductiong.  I'm using 
the servo circuit from Ben Fleming's _The EDM How-To Book_  ( based on a 
SN754410NE and LM-339 ) to drive an electrode of .003 brass wire held in 
a modified pin vise over a bath of deionized water.  My initial runs 
have burned clean .003 lines in 1 ounce copper glass epoxy board with 
out burning the substrate at 60 inches per second.  Not too bad!

I'm thinking about an electrode  design using .003" ( or finer ) brass 
wire feed through a plastic shield/electrolyte feed tube and the gap 
controlled by a stepper driving a worm on a gear which would drive a 
wire spool.  The gap could then be controlled by a simple step in step 
out  sequence while the electrode chuck could be kept compact and light 
in weight.

Finally a new area of inquiry.  Using microwaves to burn the copper ( 
and possibly the substrate for through holes ).  See the October 18 2002 
edition of Science magazine for an article on a microwave drill!

I'll try to put more time into the EDM project now that I can see the 
light at the end of the tunnel on my Willys restoration.

-- 
Curtis W Richards

--
"Law and liberty cannot rationally become the objects of our love,
unless they first become the objects of our knowledge." 
--James Wilson



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