Re: Building an RSG

Hi Alan, and all,

Alan Sharp wrote:

> ....
> But I think I actually have the answer, my grinder - a machine
> made for spinning sparking discs! 1/2 HP, 3000 rpm motor (UK has
> 50Hz mains). Heavy duty bearings - made to take off axis pressure.
> (snip)
> The only thing I can't do is grind the flats on the motor to make
> it sync.

The grinder sounds ideal if there is little endfloat in the shaft.
It should make mounting the Tufnol disk a bit easier,  and 1/2 hp
is more than enough torque !

If you leave the motor un-modified it will run asynchronously around
2900 rpm.  A higher break rate will be needed to avoid problems with
surging and resonant rise as the firing point is constantly moving
along the supply waveform.  Above 200BPS this problem dissapears
very quickly.  I would still recommend modifying the motor, even if
it meant I had to hire another grinder to do the grinding !

> .... So its a variable speed RSG.

I don't know if you can control the speed of the motor in the grinder
using a Variac.  If it is a universal motor (with brushes,  and a
wound rotor, etc.)  then you will be able to control it OK.  The
3000rpm rating sounds like an induction motor to me,  and this might
not change speed smoothly if you decrease its supply voltage.
Have you tried this with the motor under load ?

> When I come to do it, I'll use the 1/2" thick tufnol from RS
> components.

I used 8mm Tufnol also from RS and have no problems at 1500RPM.

> Now all I need is time!

Tell me about it !

					- Richie,

					- In Sunny Newcastle.