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Re: [TCML] Spark Gap Motor and Control

I want to glom on here.  I built an ARSG around a woodworking router.  It was a very compact 1HP unit by Black & Decker.  I picked it up at a yard sale for next to nothing.  It had only a 1/4" chuck.  I used a 1/4" machine bolt for the shaft.  I cut the head off the bolt.  The smooth shank of the bolt went into the chuck.  The threaded end took the disk.

The disk was unique too.  I rescued some sheets of unclad G-10 circuit board stock from the dumpster at work.  They were only 1/16" thick, so I cut out four 6" disks and sandwiched them together, taking care to orient the grain in different directions.  I'm no machinist, so I drew circles on the G-10 using a compass and cut them out with a jigsaw.  I made reasonably true center and electrode holes with a drill press.  To keep it simple, I used only two flying electrodes.

The electrodes were 1/4" threaded brass rod and hex nuts.  I used a 1" gap in my vice to file the electrodes to exactly the same length, then balanced the electrode & hex nut assemblies using a sensitive ammo reloading scale.  Finally, I chucked the disk into a hand drill and held a file against the edge of the spinning disk to true it up.  This was not as much trouble as it sounds.  I put the thing together in a couple of afternoons after work.

Despite the crudeness of my methods, vibration was negligible.  A few dabs of lok-tite kept everything well--tight.  This was a very effective ARSG for my MOT & pig-based coils at moderate AC input power.  Speed control was effortless using a regular 600W lamp dimmer.  Even at full blast, the disk never showed any signs of stress.  I figured the soft brass electrodes would quickly burn away.  Not true.  I never had to replace them.  Erosion was slow and predictable.  An occasional lick with a fine file was all they needed for maintenance.

A few years back I removed the G-10 disk to experiment with an Aluminum disk.  The Aluminum disk didn't work out, and I misplaced the G-10 disk!  Rats!  Adding insult to injury, Katrina soaked the router in flood water.  Double rats!  Incredibly, the router still works.  I cleaned it up, dried it out for a couple of weeks, and it runs like a champ.  I guess "universal" hand tool motors are really tough.  I still have enough PCB scraps to make a new disk.  Maybe I'll reconstitute this gap someday.



--- On Sat, 10/25/08, bunnykiller <bunnikillr@xxxxxxx> wrote:

> From: bunnykiller <bunnikillr@xxxxxxx>
> Subject: Re: [TCML] Spark Gap Motor and Control
> To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
> Date: Saturday, October 25, 2008, 8:22 PM
> Hey Robert...
> Looks like you have a good match on the controller compared
> to the 
> motor, but the price for the motor seem a bit high.
> Consider something 
> like a router ( wood working type) which will be capable of
> a 1/2" shaft 
> instead of a 3/8 shaft. HP would be comparable for about
> 1/2 the price. 
> ( routers run about 65-85$)
> Next thing to consider, the RPM rating and the material
> needed for the 
> disc to be used. If you run the motor up to speeds above
> 2000 RPM ( more 
> than 25% of the controller ) your disc must be capable of
> handling the G 
> forces that will be present with the chosen electrode
> assembly. 
> Remember, the more weight your electrodes have and the
> higher the RPM's, 
> the more force is applied to the edge of the disc, if the
> electrodes are 
> heavy and the distance from the edge of the disc to the
> electrode is 
> "thin", the higher the chance of the electrode
> has a capacity to tear 
> through the disc material and become " shrapnel
> projectiles".  For 
> example, an electrode on a disc of 9" dia. at 1800 RPM
> breaks loose, it 
> has the velocity of approximately 45 MPH... at 10,000 RPM (
> 5X that of 
> 1800rpm)  450MPH ( if my math is correct) 660 FPS... that
> pretty much 
> comparable to a pellet gun firing a 250 gram load.... ouch!
> Also, since the motor will be controlled to
> "whatever" rpm you desire, 
> it will become a SRSG at 900, 1800, 3600, 7200 RPM with
> associated BBP's 
> at 60 120 240 480 if the timing is phased right ( it could
> happen ;)  )!
> Considerations to ponder...
> G-10 Phenolic disc material 3/8 - 1/2" thick 8 -
> 12" dia
> Tungsten electrodes 3/16 - 5/16 dia.
> 1/2" of material from edge of electrode to edge of
> disc.
> Other than that, it looks like you are on your way to a
> good rotory gap....
> Scot D
> Robert Davies wrote:
> >Hello All,
> >
> > How do you think this would work for my ASRSG
> >
> > 
> >
> > 
> >
> >  
> >
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