[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
RE: [TCML] G-10 blistering
My collars are 7/8" long (threaded portion only), which means I have
1/4" of threaded bolt (these collars are threaded into the G10) exposed.
I then machined the aluminum nuts to resemble jam-nuts (about 3/16"
thick) that screw onto the exposed threads to further ensure everything
stays tight. The heads of the bolts were also machined down to about
3/16" thickness to reduce the air drag as well. The electrodes
themselves extend at least 1/2" out either side of the bolt (they are 2"
long).
Yeah, when this baby gets up to speed, it's a bit scary, but it all
stayed balanced. As much air as this thing is whipping up, I can't
imagine the contacts getting too hot, but I'm not yet running the power
you are - not yet :)
-----Original Message-----
From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
Behalf Of David Rieben
Sent: Saturday, June 21, 2008 7:40 AM
To: Tesla Coil Mailing List
Subject: Re: [TCML] G-10 blistering
Hi Terry,
Wow, where did you locate 1/2" threaded aluminum bolts?
I suppose 1/2" aluminum round stock would also work.
How thin did you "slice" the aluminum bolt to make your
collars and how much of the flying electrode is left pro-
truding beyond your "collar"? My collars were for a 3/8"
shank (since my flying tungsten electrodes are 3/8" in dia-
meter) and are each 3/8" thick. Since they are also made
of aluminum, they don't add a tremendous amount of mass
to the flying electrodes but they only leave about 1/4" of
the 1 1/2" long electrodes protruding beyond the surface
of each collar, since my G-10 disc is 1/2" thick. If sparking
to the aluminum collars becomes a problem, I may have to
upgrade to longer tungsten flying electrodes. Of course this
would add considerable mass to the whirling disc, since tung-
sten has the same density as gold (19.3 gm/cc)! I beleieve
as long as I could keep it reasonably balanced, my 2.5 HP
variable speed DC treadmill motor could handle the addi-
tional load, though.
David
----- Original Message -----
From: <toxandale@xxxxxxxxxxxxx>
To: "'Tesla Coil Mailing List'" <tesla@xxxxxxxxxx>
Sent: Saturday, June 21, 2008 4:21 AM
Subject: RE: [TCML] G-10 blistering
>I made aluminum collars for my electrodes with 1/2" aluminum bolts
(then
> drilled a 1/4" hole down the axis of the bolt. Then I tapped an 8-32
> thread
> for a set screw to hold the electrode in place)
>
> One thing I did notice was that the extra material poking out from the
12"
> disc (the collars) did create enough air drag that my SRSG (with two
flats
> machined into the rotor for 3600 RPM) would jump out of phase
regularly. I
> finally machined the collars so no extra material was exposed, and
then
> removed two of the contacts that would be passing through zero volts
(it
> now
> has 6 electrodes instead of 8). This reduced the drag to a point that
the
> SRSG maintained synchronization.
>
> Un-Terry
>
>
>
> -----Original Message-----
> From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
Behalf
> Of David Rieben
> Sent: Monday, June 16, 2008 8:47 PM
> To: Tesla Coil Mailing List
> Subject: Re: [TCML] G-10 blistering
>
> Hi Phil,
>
> I like the clamp-on shaft collar idea and went ahead and ordered 16
> of those aluminum ones from McM-C today. As long as I place one on
> each end of each of the 8 flying electrodes, I don't see why the
rotary
> disc would need to be (re)balanced, so long as it was decently ba-
> lanced in the first place and the motor is suffciently strong enough
to
> spin the additional mass of the added collars. This should definitely
in-
> crease the thermal mass and the aluminum would also conduct heat
> away from the tungsten "core" electrodes better.
>
> David Rieben
>
>
>
>
> ----- Original Message -----
> From: <FIFTYGUY@xxxxxxx>
> To: <tesla@xxxxxxxxxx>
> Sent: Sunday, June 15, 2008 7:27 AM
> Subject: Re: [TCML] G-10 blistering
>
>
>>
>>
>> In a message dated 6/14/08 2:00:43 P.M. Eastern Daylight Time,
>> bartb@xxxxxxxxxxxxxxxx writes:
>>
>>> I have 8 flying electrodes on my disc. Each of these flying
>>> electrodes is a 3/8" x 1.5" long solid tungsten rod.
>>
>> Some notes with bare tungsten press-fit to G-10:
>>
>> When I assembled the 3/8" tungsten rods into my 12" G10 disk
(sound
>> familiar?) I did some testing in a scrap piece of G10 (the corners
of
>> the
>
>> squares
>> I cut off to make a circle from the square piece of 3/4" thick G10).
I
>> drilled a hole with the same distance-to-edge as the actual rotor
holes
>> and reamed
>> it out to .373" to begin with. The rods were .375" dead-nuts, to the
>> best
>
>> of
>> my measuring ability. I had a .374" reamer in case they ended up too
>> tight.
>> It took about two tons of force to get the rods into the holes, or
to
>> adjust
>> them once they were in. So I reamed all 8 rotor holes to .373".
>> Another thing I wanted to check was the retaining ability of G10
at
>> elevated temperatures. So with a torch and a non-contact thermometer
I
>> carefully
>> warmed a rod up to 300 deg F (past the 284 deg F max service temp of
>> G10!).
>> Guess what? That press-fit rod now freely slid back and forth in its
>> hole!
>> After it had cooled, it was nowhere near a tight fit as it had been.
>> There has been discussion here that adding a retaining setscrew
thru
>> the
>> rotor edge actually weakens the G10. Maybe the best bet is clamping
>> shaft
>> collars:
>>
>> From McMaster-Carr (_www.mcmaster.com_ (http://www.mcmaster.com)
):
>>
>> 6157K13
>> One-Piece Aluminum Clamp-on Shaft Collar 3/8" Bore, 7/8" Outside
>> Diameter,
>> 3/8" Width
>> In stock at $2.25 Each
>>
>> or if you prefer thermal mass over conductivity:
>>
>> 6435K13
>> One-Piece Clamp-on Shaft Collar Black-Oxide Steel, 3/8" Bore, 7/8"
OD,
>> 3/8"
>> Width
>> In stock at $1.99 Each
>>
>> The plain steel would probably suffer in that environment. They
also
>> offer stainless steel for substantially more cost and lower thermal
>> conductivity.
>>
>> I've seen some folks use shaft collars as the sole means of
retention
>> on
>> their RSG's. Of course you'd have to re-balance after adding the
collars
>> to
>> both sides of the rods. Would add about $40 for my 8-electrode RSG,
but
>> certainly seems worth it if it keeps the tungsten slugs from
escaping!
>> Might have
>> to watch out that the collars don't arc to the stationary
electrodes.
>> Some folks use rings on the faces of the disk, but I dunno how
they
>> secure the rods. I also dunno how you would get heatsinking from it
>> unless you
>> tack-welded the collars to the disk after everything was assembled.
>> Maybe the best would be to use a solid aluminum rotor with an
>> insulated
>> hub or belt drive. I've got all the parts for a timing belt drive,
but I
>> figured I'd start simple.
>>
>> -Phil LaBudde
>> Center for the Advanced Study of Ballistic Improbabilities
>>
>>
>>
>>
>>
>>
>> **************Vote for your city's best dining and nightlife. City's
Best
>> 2008. (http://citysbest.aol.com?ncid=aolacg00050000000102)
>> _______________________________________________
>> Tesla mailing list
>> Tesla@xxxxxxxxxxxxxx
>> http://www.pupman.com/mailman/listinfo/tesla
>
> _______________________________________________
> Tesla mailing list
> Tesla@xxxxxxxxxxxxxx
> http://www.pupman.com/mailman/listinfo/tesla
>
>
> _______________________________________________
> Tesla mailing list
> Tesla@xxxxxxxxxxxxxx
> http://www.pupman.com/mailman/listinfo/tesla
_______________________________________________
Tesla mailing list
Tesla@xxxxxxxxxxxxxx
http://www.pupman.com/mailman/listinfo/tesla
_______________________________________________
Tesla mailing list
Tesla@xxxxxxxxxxxxxx
http://www.pupman.com/mailman/listinfo/tesla