On Mon, 13 May 2013 21:47:36 -0400, John
wrote:

snip
What other machine could you use to cut an internal keyway in a blind hole?
snip

light bulb edm

rig up insulating tool holder and use mill. Slow but price
is right. You can use hex or spline key as electrode to
burn internal hex or spline to size. Article shows lash-up
using drawer slide and all-thread for vertical movement.

http://pico-systems.com/edm.html



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for fancier dedicated machine see
http://www.homeshopmachinist.net/sto...oredirect=true
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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.
==========

http://bbs.homeshopmachinist.net/thr...iagnostic-help

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Let the group know how you make out.


--
Unka' George

"Gold is the money of kings,
silver is the money of gentlemen,
barter is the money of peasants,
but debt is the money of slaves"

-Norm Franz, "Money and Wealth in the New Millenium"