Re: [CAD_CAM_EDM_DRO] AC Speed Controller for Lathe: Meat or Accident?

On Wed, 17 Sep 2003 10:32:47 -0000, you wrote:

>Swarfer-breatheren,
>
>I seemed to have (accidentally) bought myself a massive big old lathe
>at an auction. When I picked it up however, I found that the motor
>was some horrid 3-phase electical fire with a rats nest in it, so I
>dropped this and decided to just buy a new one of ebay. However: as
>I'm now missing the belt-drive and motor assembly I'll have to make
>this up.

Congratulations... I think... <grin>

>
>I thought this would be the best place to ask this: I'm thinking
>about building my own AC motor speed controller (with some
>thyristors) and just leaving the motor belted on one setting or the
>other. I was wondering what advice people would have on this? I'd
>have asked this on another forum, but as you all are so terribly
>nice, and experienced with this type of thing I thought I'd ask here
>(and hey! I'll probably convert the lathe to CNC in the future
>anyway. :) )

Depending on motor type, a speed control on an ac motor might be less
useful than otherwise. I'm not an expert on motors, though.

>
>So what's the deal? Is this good science, or bad science? Will the
>lower voltage mean the motor will turn really slow, but also have no
>torque what-so-ever? Should I use some other kind of circuit? Or is
>this is all just a terrible idea that's going to wreak havoc on the
>electrical grid for blocks around as I throw rude-pulses at a 2KW
>motor? Should I use a DC motor instead? (I want to do this on the
>cheap, really)

One thing you might be able to do is to find yourself an old treadmill
motor, the bigger the better, which *might* give you enough power.
Those can be run with a commercially available speed controller, or
perhaps an adaptation of what was in the treadmill. Not sure on
ratings, though, and available horsepower.

>
>BTW> This is a BIG old lathe! 5foot long and weighs.. well.. the
>tailstock weighs about a third of my weight. :P
>
>Thanks for your advice!
>
>

Harvey