Re: Ball bearings

Neon John wrote:
>I would expect that.  Bearing steel just doesn't anneal very much.
>I have drilled it using solid tungsten carbide bits but it's kinda
>like pushing string - neither much fun nor very successful.

I have had good success using drills marked "M-42".  Our shop has a set of 
these bits - and for whatever - they cut just like mad!  I'm told this is a 
grade of cobalt steel.  Can anyone verify?

In my opinion - I am not overly impressed with the life or cutting ability 
of those golden bits "Titanium Nitrided".  Anyone have experience to the 

>>Think the EDM would
>>work well, but didn't think it was a high-voltage proposition.  Details
>>please?  Think Lindsay has a book on EDM, and should probably pick it
>I don't have Lindsay's book but I hear it is very good.  My frame of
>reference is an old Pop Mechanics article back in the 60s on a
>homemade EDM setup.  Used a plate tranny, some caps and ordinary
>copper wire as the effector.  The whole operation was done under
>kerosene.  Works quite well.  Biggest application for me has been to
>machine out broken taps.  Since this is just a fancy, controlled
>version of the same process that pitts the terminals of a cap that's
>shorted, it should machine just about anything that will conduct
>electricity.  BTW, lindsay has another little book on building a tap
>removing machine that uses EDM and a vibrating engraver.  Looks real

It is easy to do home EDM.  Many magazines have covered this topic.  In fact 
- the use of graphite EDM electrodes is about the only decent way to shape 
("machine") tungsten slabs into useable shapes (according to my old books).

EDM will certainly drill right on through any sort of steel.  Takes a bit of 
time.  Here is how I did it:
1) 70 volt 8 amp power supply, DC.
2) 60-300 uf (adjustable via switches) capacitor bank hooked to the above 
supply with a series 8-ohm resistor for current limiting
3) Hook one end of the cap bank to the work, and the other to the electrode. 
  I don't recall if the polarity mattered or not.  I used a mechanical 
pencil lead (0.5 mm, and mostly graphite).  Others have used hollow brass 
tubing with sume good results.
4) Lower the electrode into the work, stopping as long as the arcing 
continues.  You must pump a dielectric fluid through the arc cavity.  I used 
distilled water but other have used wd-40, diesel, kerosene etc.  DON'T burn 
yourself up! :)

In my case I had a stepper motor and a small processor rigged up so that it 
would advance the electrode only while the cap bank was >60 volts, or 
something like that.


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