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Where do I get Tungsten welding electrodes?




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From:  Edward J. Wingate [SMTP:ewing7-at-frontiernet-dot-net]
Sent:  Friday, March 20, 1998 6:14 PM
To:  Tesla List
Subject:  Re: Where do I get Tungsten welding electrodes?

Tesla List wrote:
> 
> ----------
> From:  D.C. Cox [SMTP:DR.RESONANCE-at-next-wave-dot-net]
> Sent:  Thursday, March 19, 1998 1:40 AM
> To:  Tesla List
> Subject:  Re: Where do I get Tungsten welding electrodes?
> 
> to: Cliff
> 
> TIG tungsten welding rod is fairly brittle.  If the RSG is even slightly
> out of balance or wears unevenly dangerous mechanical resonance conditions
> can occur that will cause a slight vibration in the material.  This could
> lead to stress fractures and eventually a rotor explosion.  We prefer to
> use the short screw-in type (1/2 inch dia) and thread them into 1 1/2 inch
> long x 1/2 inch dia brass rod which is press fit into the G-10 rotor
> material.  The TIG rods are ok in smaller 6 inch dia rotors but unless you
> have the experience of an Ed Wingate or other machinists its not a good
> idea to try to make a TIG rotor yourself -- mostly due to its brittle
> nature.  Would suggest a competent machinist do the work on a turntable and
> a gram scale to carefully weigh the components -- also spin balance at up
> to 6000 RPM.
> 
> DR.RESONANCE-at-next-wave-dot-net
> 

> > From:  Mark S. Rzeszotarski, Ph.D. [SMTP:msr7-at-po.cwru.edu]
> > Sent:  Wednesday, March 18, 1998 4:55 AM
> > To:  Tesla List
> > Subject:  Re: Where do I get Tungsten welding electrodes?
> >
> > Hello All:
> > Cliff said in part:
> > >I noticed that you mentioned that .38 in tungsten tip rods would be good
> > >to use on the stationary part of a rotary gap. Is there any reason that
> > >they can't be used on the rotating part of the RSG?
> >         I have not built a rotary yet but have studied their design.
> They
> > are EXTREMELY DANGEROUS devices, especially if you spin them up over 5000
> > RPM which some folks do.  The centrifigal forces make them a lethal
> weapon.
> > Perhaps one of the experienced rotary folks can step in here and discuss
> > design a bit.  A couple of folks on list are experienced machinists who
> have
> > built real masterpieces and understand the need for safety.  (Ed, Dave,
> > Richard, Bill, Greg, D.C., others step forward at this time.)
> > Regards,
> > Mark S. Rzeszotarski, Ph.D.
> >

All,

D.C. is right about tungsten rod being very brittle. With the melting
point of tungsten being somewhat higher than 6000 degrees F. it isn't
practical to melt and cast it to produce tungsten rod. Pure tungsten rod
is produced by heating and pressing tungsten powder into a form under
great pressure ( called sintering) and then cylindrical grinding it to
size. This process makes the finished product brittle and prone to
fracture from shock stresses.

With all of that stated, I have been using solid tungsten rod for years
to build rotary gaps for my own use and for other coil builders and to
my knowledge have not had a stud fail in service. The tungsten is tough
enough to take rather significant amounts of centrifugal force in the
spinning rotor but a collision with a stationary stud will cause it to
shatter like glass. Other factors such as rough handling when machining
or dropping onto a hard floor can cause fractures that could cause lead
to failures in use. Rotor balance is also critical to keeping moving
rotor studs from getting up close and personal with stationary studs at
high speeds. I also highly recommend using ball bearing motors because
they have almost no end play. I have seen common sleeve bearing motors
with as much as .125" of end play. Not a good thing for a high speed
rotary gap!

Safe coiling,

Ed Wingate