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RE: AMRAD Spark Gaps
Original poster: "Oxandale, Terry by way of Terry Fritz <twftesla-at-uswest-dot-net>" <Toxandale-at-SPP-dot-org>
My sections (plates) had an arcing diameter of about 1.25" diameter. It
was perfectly flat in this part and the arcing pattern (rough, stippled
surface) was extremely even throughout this entire area. The thickness
of the brass plates are unknown (I guess it's time to pull it out of
packing and look at it) but I would guess they were about 1mm. I just
happened to have about 2 dozen of them (innerds from a 500kv lightning
arrester) and used washers as arbors (a grade 8 washer with a large ID
on top of disc would press disc down over a smaller OD washer under the
disc) to press the shapes.
Un-Terry
> ----------
> From: Tesla list[SMTP:tesla-at-pupman-dot-com]
> Sent: Saturday, December 30, 2000 6:09 PM
> To: tesla-at-pupman-dot-com
> Subject: Re: AMRAD Spark Gaps
>
> Original poster: "bob golding by way of Terry Fritz
> <twftesla-at-uswest-dot-net>" <yubba-at-clara-dot-net>
>
> Hi Terry, All,
> How thick where the sections on your gap? I thought a slight
> concave
> depression in the sections
> might work. It would be easy to incorporate at the design stage, but
> how
> much and how thick each
> section should be is beyond me at the moment. I am sure someone on
> the
> list knows how to work it
> out. The potential problem might be that it will start to arc at the
> edges
> and stay there.
>
> cheers
> bob golding
>
> Tesla list wrote:
>
> > Original poster: "Oxandale, Terry by way of Terry Fritz
> <twftesla-at-uswest-dot-net>" <Toxandale-at-SPP-dot-org>
> >
> > I'm not an industrial engineer, but I can hold my own in a
> mechanical
> > environment. When I built this (and I may have stated this earlier)
> > device, other than gasket problems (which were a concern even before
> I
> > built it but I was just using what I had on hand to see if it would
> > work), the only other problem was the uneven expansion of the discs
> > during the warm-up (initial arc time). the arcing side of each disc
> > would get hotter than the opposite (non-arcing) side, and thus this
> > uneven expansion closed the gap somewhat. Now multiply this times
> the
> > number of gaps, and you could have a significant problem with many
> gaps
> > (which is why I think mine worked best at about 5 to 6 gaps).
> Intuition
> > tells me that if we make the center arcing surface too large in
> area,
> > that this expansion problem will be exacerbated. I don't know if a
> > thinner disc would curve less than a thick disc would (due to the
> > temperature evening out quickly). Ideally you would want to use a
> single
> > disc that is symmetrically convex (like a lens) or like two hats put
> > together at the brim. This way, arcing would occur on both sides of
> the
> > disc, but in my case, this entailed machining that I did not have
> > available to me at the time. This is a most resourceful bunch of
> folks
> > on this list so I know somebody is going to come up with even better
> > ideas (other than a lot of elbow grease and grit like we used to do
> to
> > make telescope lenses)
> >
> > Terry Oxandale
> > > ----------
> > > From: Tesla list[SMTP:tesla-at-pupman-dot-com]
> > > Sent: Friday, December 29, 2000 9:14 PM
> > > To: tesla-at-pupman-dot-com
> > > Subject: Re: AMRAD Spark Gaps
> > >
> > > Original poster: "bob golding by way of Terry Fritz
> > > <twftesla-at-uswest-dot-net>" <yubba-at-clara-dot-net>
> > >
> > > > Hi All,
> > >
> > > > I have been putting some thought into how to make an accurate
> > > amrad
> > > type gap and have come to the
> > > > conclusion that the best way would be to stamp out the pieces on
> a
> > > fly
> > > press. This would involve
> > > > making a die. I have been talking to a friend with a lathe
> milling
> > > machine and a fly press. He looked
> > > > at my drawings and said if I go round and instruct him on what
> we
> > > want
> > > ,and provide the materials he
> > > > is quite happy to turn up a die for us. The materials are no
> > > problem, the
> > > time is my own and I can
> > > > always get copper from the scrap yard. So if we are going to do
> this
> > > I
> > > need to know what dimensions
> > > > we should go for. I thought 2" copper pipe spit down one side
> would
> > > be a
> > > good start. There is always
> > > > lots of this ,and it is new so no cleaning to worry about. It is
> > > also
> > > easy to cut into short lengths
> > > > with a pipe cutter. This will give us a 5" x 5" square and
> about 1
> > > mm
> > > thick. Of course I will grab
> > > > any sheet I find. as my friend has a small guillotine. What
> > > diameter
> > > indent should we go for?. If
> > > > anyone has any ideas let me know. Still have to work out the
> gaskets
> > > but
> > > if we start with something
> > > > pretty flat is should help. I like terry's design, as this makes
> it
> > > simple to make the blanks, and
> > > > if it is enclosed in a sealed box one could put a fan on the end
> for
> > > cooling. If anyone else wants to
> > > > experiment let me know and I will send them some blanks at
> copper
> > > scrap
> > > prices plus postage.
> > > > (Currently around £1.25 (about one dollar) a kilo) to experiment
> > > with. If
> > > it all ends in tears you
> > > > could always use them for coasters.
> > >
> > > cheers
> > > bob golding
> > >
> > > >
> > >
> > > >
> > > > > > So they did. And so did I when I built mine. A real pain.
> > > > > > A right royal major pain. Mine started out as two inch
> > > > > > diameter disks 1/16 inch thick. With an 80 tooth-per-inch
> > > > > > piercing saw I converted them to washers. With a sheet of
> > > > > > sandpaper stapled to a piece of wood I sanded them down to
> > > > > > around 1 - 1,1mm thin. Lost some fingerprints and blood in
> > > > > > the process. With my Unimat 3 and a grindstone I got them
> > > > > > very nearly flat and parallel. I started with 40 disks. I
> > > > > > got 15 or so washers. I smeared silicone high vacuum grease
> > > > > > (stable to over 200C) on them to seal them against the gaps.
> > > > > >
> > > > > > They *still* leak ;-)
> > > > > >
> > > > > > Webpage coming "real soon now" but probably not this year
> > > > > > :-)
> > > > > >
> > > > > > Dunckx
> > > > >
> > > > >
> > > > >
> > > > >
> > >
> > >
> > >
>
>
>