Re: Rotary GAP

Hi Travis,

A picture is worth a thousand words...  See the files at:



The first is a bunch of pics of my gap and the second is on motor
conversion to a sync motor.  These will get you started...

A few more comments below...

At 08:43 AM 08/25/1999 -0600, you wrote:
>Tesla List wrote:
>>         Synchronous gaps can always fire at exactly the same time on the 
>AC cycle.
>>  Thus, you can fire the gap at just the peak of the AC voltage
>> continuously.  This will prevent energy being wasted by firing the primary
>> at less them max voltage.   A non-sync rotary my only deliver half the
>> power of a true synchronous gap...
>> A synchronous motor turns at a rate EXACTLY proportional to the AC line
>> voltage where other motors turn about 50 RPM less.  With a normal motor you
>> have no control over gap timing where with a synchronous motor you can get
>> excellent timing control.
>I need to look into making one. I have the basic idea but I need some 
>details. ;)
>What can I use for a motor? I noticed that the local hardware store has some 
>for swamp coolers. I think the box said they are induction motors. I'm 
>planning to use

I would get a ~1725 RPM 1/4 or 1/2 HP induction motor.  The faster ~3500RPM
motors are really fast and balance and things flying off can get really
critical.  These motors are common to run belted fans, tools...

>a pig as a power supply, but I wouldn't mind being able to use it on NST 
>coils as
>well. Do I want Sync or Non-Sync? And do you know if those motors can be 
>modified for
>Sync if needed?

If you want to run something really big then get a 1/2HP (or maybe bigger
motor) I am not an expert on all this so others will know more than me...
I think sync is best for a NST.  Many people run non-sync motors with pole
pig systems...

>I read your post about making the disc with a belt sander, it seems that 
>would work.
>How do you keep the assembly from wobbling? How did you balance it? I guess 
>I could

At 1800 RPM balance is not too hard.  Just be as careful as you can and
leave extra space on the rim incase you have to have it balanced with a
lathe.  I just let the disk turn freely and the heaviest spot rotated to
the bottom.  I then added a few small washers until it seemed not to have
any heavy spots anymore.

>get a machinest to make the disc for me. How are the electrodes secured in 
>the disc?

I used bolts that held themselves.

>I'd like to go with the tungsten electrodes, seems that they are best suited 
>for this.

I used bolts to give better cooling.  Thin tungsten is sort of hard to keep
cool.  I added a few fins made from washers to help the cooling too.  See
the pictures in the above file.

>Oh, how did you secure the disc to the motor?

I got a replacement 1/2 inch drill chuck from the hardware store.  They run
about $15 and have a 3/8 - 20 (?) threaded bolt hole in the end.  I simply
bolt the rotor to the chuck and clamp it on the motor shaft.  This has
worked perfectly for me. 

>Seems pretty simple to make them as long as I'm carefull and put it in a box 
>just in
>case it blows up. Is there anything else I should be aware of?

Look at the files and that should answer most of your questions.  Also,
many gaps are pictured around the web ring so look around and get all the
ideas you can.  I would suggest making it big, heavy, and rock solid.  My
"little and cheap" rotary gaps have not done well at all.  I have heavy 3/4
inch oak all around the rotor to catch any parts that may want to fly off.
I have a lot of hardware on the rotor but it is all very secure.  However,
if i forget to tighten something or it crashes the wood will stop it bits
from getting away.