RSG opinions?

From:  Peter Electric [SMTP:elekessy-at-macquarie.matra-dot-com.au]
Sent:  Wednesday, April 08, 1998 7:00 AM
To:  Tesla List
Subject:  Re: RSG opinions?

Tesla List wrote:

> ----------
> From:  RMC [SMTP:craven-at-globalnet.co.uk]
> Sent:  Sunday, April 05, 1998 4:37 PM
> To:  Tesla List
> Subject:  RSG opinions?
> I can buy a new 6" bench grinder in England from B & Q for twenty
> quid.
> It is a 3000rpm  half-HP motor (synchronous, I believe i.e. not a low
> slip induction motor) and is intended to run a pair of grinding disks
> (one on each end of the motor shaft).

I have never seen a synchronous grinder motor. In fact, the hunting
effect of such a motor as it starts up would make it less than ideal,
but if it truly is syncronous, buy it!

> If the effective mass of the RSG disk is less than or equal to that of
> the grinding wheels it is replacing (such that torque loading will not
> change), I might be able to modify the bench grinder to take at least
> a 9" or even a 12" disk.

Air friction is the problem, not mass. A larger disk has a much greater
air drag effect. Still, I use a 1/4 HP sync motor to spin a 6" disk so
yours should spin a 10 or an 8 without trouble.

> My intention is to make a couple of disks from Tufnol or similar rigid
> insulator, with 12 contacts. The contacts will either be
> tungsten carbide machine tool inserts    or
> Copomel tungsten/copper (70/30)
> these two materials cost less than elemental tungsten but have similar
> relevant properties i.e. they don't melt and they're very hard. The
> expense
> is still high and it means that it might be better for me to buy a
> ready-made
> RSG from BillWysock, for example.

Why don't you just use replaceable copper elecrodes in larger brass
bushes for thermal conduction. Copper conducts exceptionally well, lasts
OK but is dirt cheap to replace when worn and is very easy to cut.

> I will have four static contacts such that the switching path is onto
> and off both wheels: 4 series breaks. This could be doubled up by
> then going back through the disks on an opposite contact, so to speak.
> This might negate the need for A Richard Quick cylinder quench gap.
> It's for a 10kV primary running at 3-4 kVA upto 10kVA.
> I would welcome :
> 1. Comments on using 2 wheels and upto 4 or 8 breaks in series
> 2. Comments on Copomel vs tungsten carbide vs tungsten vs thoriated
> tungsten at 10kW
> 3. Comments on using 6" diameter rotors

I run a 6" rotor with four rotating electrodes at 1 Kw and I find the
arc noticeably stretches before extinguishing. At 10Kw the arc is
unlikely to extinguish before it hits your next electrode. I reckon you
need at least a 10" rotor .


Peter E.

> Any comments or criticisms would be very welcome. My first RSG was a
> bad job due to poor motor end-float and the fact that I used stainless
> steel. And the fact that I'm not a mechanical engineer.
> Richard Craven, Malvern, England.