Re: VFD for a 15HP CNC lathe

Scott,others,

I have "been there" and "done that".
I replaced an 8HP Per. Mag DC spindle motor on my cnc lathe with
a 15HP 3phase Hitachi from Automation Dir.
Had to go with 15HP to get
near same low end torque as DC setup. This machine is a 5C
spindle, comperable to a Hardinge CHNC. It has no gearbox.

Inverters are -not- as economical as they first appear. While a DC
drive is costly, all the periferals needed in addition to a VFD can
add up fast. I had trouble with noise radiation, and the CNC was not
seeing the marker pulse on the spdl encoder. This little detail was
causing all sorts of trouble with threading, and accurate lead pickup.
Finally, after chasing the problem and changing encoders 3 times, I
figured it out. Had to add all the inductors, EMF filters, chokes,
etc,etc. AND shield supply leads and motor leads. It threads fine now,
and I have cut threads from 8 to 24 TPI at 700-2500rpm.

If you go over 15HP with the
hitachi VFD's, you have to buy a seperate braking unit (in addition to
braking resistors). Sometimes the BU can cost as much as the drive!
I used a small electric stove element for the braking resistor, works
great.

I really do like DC drives (for spindle applications) much better,
except for the cost. DC motors still pull harder at near zero RPM, for
a given horsepower, in my opinion. The speed regulation is much
closer, and the drives are electrically "tighter" also, compared with
a VFD's "mushy" torque lag.
Should point out that I went with a flux vector drive, and the
optional encoder feedback board. Supposed to tighten up the
speed/torque response. Adds additional cost too, which was aprox.
$3300 total.

If anyone here knows a source of (lower) cost bare bones DC drives in
the 15-20-30HP range (new), please contact me offlist, I'd love to
hear about them. Need -10/+10 or 0-10VDC signal, and tach feedback
capable. 240V/3 phase input.
I have another bad drive in a Mazak lathe (15HP) and
one (20HP) on a bridge mill that need replacing.

Hope this gives you some insight on the pros/cons Scott.

dan k

--- In CAD_CAM_EDM_DRO@yahoogroups.com, fuddham@a... wrote:
> Doug,
> This lathe is an NC Clausing '79 model. It looks like a conven.
lathe.
> It will swing 22" and has a 15" hydraulic chuck on it. What do you
think
> about going with a 10 hp spindle motor? I do not plan on any heavy
cuts right
> now.
>
> Thanks,
>
> Scott
>
>
> [Non-text portions of this message have been removed]