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Re: Mississippi Mud Caps: Was, Barium Titanate Caps.

Original poster: "albert hassick by way of Terry Fritz <twftesla-at-uswest-dot-net>" <uncadoc-at-juno-dot-com>

Hi Doctor Cadd, All.   Yes, the reason for trying to find a weld type
joint to the copper plate is so that the joint will withstand the higher
kiln fired temperatures(1,800plus degrees Fahrenheit), that we will use
with our next home brew cap.  The first one was only baked at 1,200
degrees F.  We would like to stretch the limit somewhat, but we do not
think our silver soldered 'Z' clip arrangement will withstand the higher
fire. This higher fire will entail an enameled coating to the clay slug
so that we can eliminate the tedious epoxy coating affair.  We were very
fortunate to have our first cap maintain its terminal conductivity with a
regular silver/tin compound.  The 'Z' clip form, embedded partially in
the clay substrate in the vicinity of the diamond cut terminal hole
before firing was a true stroke of luck.  Then again, maybe it is
duplicative, since the silver /tin compound , once soldered and
mechanically held in place with the imbedded 'Z' clip seems to have
worked rather well with the lower fired first capacitor. Al. 
 On Mon, 07 May 2001 16:50:30 -0600 "Tesla list" <tesla-at-pupman-dot-com>
> Original poster: "Dr. Duncan Cadd by way of Terry Fritz 
> <twftesla-at-uswest-dot-net>" <dunckx-at-freeuk-dot-com>
> Hi Al, All!
> <snip>
> Thanks for the details!
> >Now, our next
> >objective is to weld/sil-fos the leads somehow to the thin copper
> plates
> Commercially, I'm pretty certain these are simply soft soldered in 
> the
> usual manner.  Any particular reason you want to go for welding?  I
> can well believe that doing this on very thin plates is difficult.
> <snip>
> >But a lot of
> >these glazes contain some lead, not sure of the content or how
> >detrimentally conductive it would be, we will have to fire these
> >compounds and see what the conductibility is of the coating.
> Lead-based glass is a pretty good insulator, but as you say, try it
> and see is the only way to be sure . . .
> >Also, we
> >will try a mostly 'white clay' base for the next capacitor, hoping
> that
> >it will produce a higher plate 'Q' than the first mostly red mud
> >capacitor did.
> That'll be interesting.
> >We are also
> >wondering about introducing a teflon 'micro sphere' compound into 
> the
> >clay as a binder/insulator, does anyone think that may help?  
> Wonder
> what
> >the melting point of teflon is?
> Eek!  No!  Teflon gives off very nasty fumes when it gets hot.  
> Toxic
> and very highly corrosive - avoid like the plague.
> >The auto body compound we used on the
> >first cap was really not a good binder/additive, since it seemed 
> to
> coke
> >up a lot on the finished fired clay capacitor(I should have known
> >better!).
> I imagine that if the kiln gets hot enough, the carbon will burn 
> away,
> especially in an oxidising kiln.  Unfortunately my limited 
> knowledge
> of ceramics technology does not extend to binders so I can't 
> suggest
> any improvements.
> >The puzzle now is proper support from the wire leads only so
> >that we can get a good glazed cover all around the capacitor body.
> Copper
> >wire leads will probably tend to sag upon high temperature heating 
> in
> the
> >kiln and may pull apart from the copper plates. We are thinking of
> >brazing, or silver brazing a brass bolt to the copper plates, 
> problem
> is,
> Ah, is this why you're thinking of welding rather than soft 
> soldering,
> to give support to the cap in firing?  You know those three legged
> ceramic thingies like the centre of a Mercedes emblem you use to 
> prop
> things up in a kiln?  (Probably called "props" ;-)  Could you rest 
> the
> cap on one of those, as it would only contact the prop at three 
> small
> points?
> >the copper plates are not really plates, they are very thin shim
> stock
> >and we have not had any luck brazing a terminal stud to the thin
> sheet.
> >Perhaps a thicker copper plate would be in order?  But it may 
> change
> the
> >whole balance of the capacitor internals as we now have them and 
> may
> not
> >be at all beneficial.
> I'm wondering since the copper is thin if you could simply fold the
> plate to give an external flange for later attachment?  Like 
> ____|____
> >Anyhoo, these caps take a lot of effort to make,
> >and I would not wish the process upon anyone! The best thing that 
> I
> can
> >say at this point is:  It was a expensive, tedious, time consuming
> >project, but we did it just to see if it could be done, even on a
> small
> >scale. If we did not already have the clay tools and kiln, arc
> welder,
> >stainless steel sieves, hydraulic jacks, etc. there is no way we
> would
> >have done this.  The clay is 'dirt' cheap!  The apparatus is not.
> >However, the final product made it all worthwhile when it actually
> worked
> >for a short time in the OBIT fired small Tesla coil.   Al.
> I'll bet!  Well done again!
> Dunckx
> Geek#1113 (G-1)
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