Re: Adequate torque from VFD driven motors?

Steve,

Your concern about the older machine not being able to handle the
torque of the larger motor needed to replace your current drive may
not be warranted. Your current drive probably is capable of far more
torque at low speeds than you will ever get out of a 5 to 10 hp motor
directly belt driven using a VFD.

Maybe your concern should be with the '50's era spindle? Is it
capable of handling the rpms needed to do efficient turning using CSS?

But, even without high rpms and CSS, just having a programmable
spindle is worth the effort IMO.

Doug

--- In CAD_CAM_EDM_DRO@y..., "scyvt" <scy@v...> wrote:
> Thanks to those who replied. The theory is now clearer, but the
> practice still poses questions.
>
> The lathe I am working on is a 50's vintage Rockwell 11" with what
they
> call a "perfected" VS 1 1/2 hp drive. (Yes, it has functioning back
> gears.) The amalgam of sliding sheaves, bearings, shafts, cams,
gears,
> etc seems awfully complex to restore and maintain compared to an
> electronic VS drive, provided that performance would be equivalent
or
> better.
>
> A VFD controlling a 3 ph motor came first to mind, since I have on
hand
> many 3 ph motors to choose from and the VFD could be run from a 1
ph
> supply with suitable derating. The suggestion that a larger than
> original motor may be required gives me some concern - doesn't that
> create a possibility of greater-than-design torque at higher speeds
> that could cause harm to the machine, or even operator if a
> catastrophic failure occured?
>
> Perhaps a dc motor and controller would be also worth considering,
> especially if that would address my concerns about low-end torque
while
> keeping the 1 1/2 hp factory spec.
>
> So, how do ac & dc spindle drives compare in terms of cost,
> performance, availability, and ease of CSS implementation. And how
do
> the several dc control approaches compare?
>
> TIA
>
> Steve Clay-Young