Q: Bridgeport Mill - Replacement motor like this?
 

Ok, so it's a 2J varispeed head...

I'm thinking... out loud... screw the varispeed with the expensive belt
and the incredibly expensive replacement motor - the mill has no motor
or varispeed pulley for the motor.

Why not a standard motor of requisite HP mounted on a plate where the US
Motor motor would usually go OR a random US Motor mill motor of 1.5 to 2
HP, standard pulley (I can always make one on the lathe...) AND a VFD??

Best of all worlds? Or nightmare?

Comments?


VFDs - what freq range is *necessary*? to 200Hz, to 400Hz??
If the motor is a 3450 RPM going from 50Hz to 200Hz makes that sucker
run damn fast!! ;_) What am I missing here...? I think the mill has a
high/low lever that is in the lower part of the head... so I'd still
have two ranges... yes?

_-_-bear

Q: Bridgeport Mill - Replacement motor like this?
 

BEAR wrote:


Ok, so it's a 2J varispeed head...

I'm thinking... out loud... screw the varispeed with the expensive belt
and the incredibly expensive replacement motor - the mill has no motor
or varispeed pulley for the motor.

Why not a standard motor of requisite HP mounted on a plate where the US
Motor motor would usually go OR a random US Motor mill motor of 1.5 to 2
HP, standard pulley (I can always make one on the lathe...) AND a VFD??

Best of all worlds? Or nightmare?
OK, there are a few problems. The vari-speed driven pulley is still
there. I suppose you could use it as a belt tensioner. But, I don't
know if the flanges have the right angle for standard Vee belts.

2nd, the vari-speed drive, OR the 4-step pulleys, give a substantial
torque increase at the low end of the speed range. With one fixed
setting, you won't get that boost. On the other hand, I haven't really
ever come close to using up the torque of a ONE Hp motor on my mill.
A VFD will only give you rated torque below the nameplate speed, and
the motor will overheat at low speeds.

Jon

Q: Bridgeport Mill - Inverter duty motors??
 

Jon Elson wrote:
BEAR wrote:



Ok, so it's a 2J varispeed head...

I'm thinking... out loud... screw the varispeed with the expensive
belt and the incredibly expensive replacement motor - the mill has no
motor or varispeed pulley for the motor.

Why not a standard motor of requisite HP mounted on a plate where the
US Motor motor would usually go OR a random US Motor mill motor of 1.5
to 2 HP, standard pulley (I can always make one on the lathe...) AND a
VFD??

Best of all worlds? Or nightmare?

OK, there are a few problems. The vari-speed driven pulley is still
there. I suppose you could use it as a belt tensioner. But, I don't
know if the flanges have the right angle for standard Vee belts.

2nd, the vari-speed drive, OR the 4-step pulleys, give a substantial
torque increase at the low end of the speed range. With one fixed
setting, you won't get that boost. On the other hand, I haven't really
ever come close to using up the torque of a ONE Hp motor on my mill.
A VFD will only give you rated torque below the nameplate speed, and
the motor will overheat at low speeds.

Jon


I'm running an Index mill now with step pulleys and I have yet to do
anything but switch the electrical hi/lo speed switch... so probably not
a big issue.

As far as I can see the "Inverter Duty" motors do mainly two things;
give even torque over a wide range of speeds (Baldor has some rated up
to 4000rpm and some as high as 6000!), and not breakdown with the pulses
from the controller...

As far as the latter, why not put some MOVs across the lines that shunt
at something less than 1kv?? Thinking that 750-800vac would be about
right to protect ur average motor...

It's not clear to me what makes the "Inverter Duty" motors different as
far as maintaining torque... anyone know?

Setting the ratios on the pulleys right, ought to permit pretty good
torque at low speeds... and yes I guess the variable pulley could be the
"tensioner"... albiet for the fatter style belt.

And, I was wondering, why not set the motor on a spring loaded track or
pivot that permitted a range of motion for the motor as the vari-speed
flanges moved apart and closer? That would keep the belt tension in a
manner similar to the spring loaded clamshell pulley arrangement??

I was looking at a nice 3hp motor C mount to put on top... extra
built-in torque for margin...

ANYONE USING VFDs???

_-_-bear