Re: construction materials

["Bill Lemieux" <gomez-at-netherworld-dot-com> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

On that fateful day 8/14/00 7:49 AM, thus spake Tesla list:

> Original poster: "acmnovak" <acmnovak-at-email.msn-dot-com>

> I'm rounding up parts for my next coil, which will utilize a sync rotary gap.
> As for the rotary, I've seen some really 'different' materials used. I was
> wondering where one might purchase g-10, or bakelite.

Bakelite (a trademark brand of phenolic resin?  I forget) is somewhat
brittle, but has high heat resistance.  It has poor tensile strength
compared to composites.

> I'd like to use G-10
> for my disk, and bakelite for my motor mounts.

Why bother using expensive and exotic materials for the motor mounts?

> Has anyone ever tried using
> hardwood for the stand?

I'm 99.44% certain I saw such a stand on Terry Fritz's synchronous rotary.

> I'm trying to make a stand as rigid and sturdy as
> possible. I was looking for lexan earlier this year, and could only find it
> in the form of cutting boards. as suggested, Ilooked in the yellow ages
> under plastics and such, but the results weren't too promising. I called
> the place that does windows and whatnot, and they wanted about $5/sq ft of
> 1/4" plexi. Is that steep or am I just really cheap?

That sounds a little pricy, but not sky high.  Around the Colorado front
range, you can get 1/4" polycarbonate (Lexan) for that price.  And 1/2"
thick LE grade (linen) phenolic laminate for $18 - $22 a square foot.  You
need to really call around to lots of places in a large metro area, to get
the best price.  If you don't live in a large metro area, call one within
driving distance, plan out all your purchases, and make one all-day shopping
trip.

> Also, what kind of electrodes are best?

Unobtanium.  This is my name for tungsten/copper sintered "alloy", and it
based entirly in subjective opinion and not measured facts.  ;-)

> I've seen some nice tungsten
> electrodes, but aparently they are hard to machine, and quite expensive.

Check out your local dart shop.  If you have access to a machine shop, then
tungsten is no harder to machine than steel.  If you don't have access to a
machine shop, it doesn't matter does it?

> However, I was leaning more towards brass. Does this stand up well to TC
> abuse? 

I have seen lots of spark gaps made of brass.  Brass has good thermal
conductivity and conductivity.  It's melting point is considerably lower
than say, steel, but I think its excellence in the other two areas make up
for that.

> I have some big pieces of brass (3/4" x 6-8") which have a porcelain
> collar. they came from an old a/c unit with a HUGE current draw. I've used
> them as high current contacts and they are showing some signs of decay...
> Is this comparable to how it will perform in a rotary as the stationary
> electrode? 

I have found that rotaries put a bit less strain on the stationary
electrodes than the other gaps I've tried, but there are "exotic"
stationaries such as the "coaxial air blast" design which I suspect would
show as little wear as the rotary.

Incidentally, I once removed all of the steel electrodes from my old high
speed (3000 rpm max, 15 electrodes) rotary and replaced them with brass.  I
saw no difference in performance, but the erosion was much higher.  I'm
still running on the same original set of bolts used for the first set of
electrodes.  Of course, most of the gap losses are in the gap itself, so
it's my opinion that electrode material will have little impact on
performance, only on reliability and maintenance.

> A while back, I heard someone say that a rotozip tool was a "must have" for
> any serious coiler... so I bought one :þ Is it true that they can cut
> through steel? I tried aluminum, and had no problems, but steel may be an
> entirely different story.

For the most part, that depends on what the cutter is made of, not the power
tool itself.

> The main reason I bought it was, I needed
> something to make clean cuts in lexan, and a decent band saw is well above
> my price range. My table saw always sucked the plastic towards the blade
> and made a jagged cut.

Ever tried a fine-tooth plywood blade with the table saw on the slowest
pulley set?

> Also, are these rotozip saw suitable for cutting G-10 or bakelite?

Bakelight is very hard to cut or machine because it's brittle.
G-100 is abrasive as heck because of the glass fibers- it quickly dulls high
speed steel cutters.  I'd recommend using ceramic inserts for machining, or
tungsten carbide tipped saw blades for cutting it.

- Gomez

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this message was made possible by: Bill Lemieux, Gomez A.D.D.ams, Arkoff
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