Re: Home-built EDM

Hi Rich,

The EDM works as you know by spark erosion.

the shortest path to a hole is to remove only those bits in the way.
ANY side movement of your electrode will cause more side sparking
than needed.

Considder that your electrode will remove any metal within about
0.002" of the path. if your electrode is dead straight and does not
wander, you can calculate ammount of metal to be removed.

a 1/8 square electrode cutting thru a 1/8 thick block will remove
metal in a hole that is about 0.127 inch square.

a 0.005 wobble will make a hole a that is larger and only cause a
slight increase in cutting time. Area is 0.0161 for the 1/8 sq as
compared to 0.0187 for the larger hole, or about 15% greater metal
removal.

a hollow tube electrode will cut faster, and that same wobble will
show up as a much longer cutting time. the error may be as large as
the wall thickness causing much more metal removal than necessary.

Also, your lightbulb resistors are limiting the speed of the spark.
try changing the wattages so both higher and lower ranges to see what
the results would be.

The sparking should be a nice buzz. Think a car with a rough idle as
a not good edm pulse, and then that engine speeding up to a smooth
purr as the proper pulse.

Dave

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Rich" <rmancini@h...> wrote:
> I just completed construction of a home-built EDM from an article
by
> Arnold Gregrich in Home Shop Machinist (October/November 2002).
> The initial test results were disappointing to say the least. Using
> plain tap water, I could hardly get any sparking at all. When it
did
> spark, there didn't seem to be enough power to start a hole, much
> less burn clean through a piece of 1/16" thick steel. I changed
over
> to deionized water with no real improvement. The sparks seem to
> wander and not concentrate in one area.
> These are the specs: Used two 3600 uf caps, a 400V rectifier and
200
> watt light bulbs in both sockets. The electrodes I tried were .062"
> mild steel welding rod, ¼" copper tubing and a piece of a
telescoping
> car antenna (chrome plated brass which didn't work at all).
> If anyone is familiar with this machine, I sure could use some tips
> on increasing performance. I need more aggressive sparking, but how
> to achieve it is the question.
> Rich