Re: Converter or Inverter for 2hp Bridgeport mill

Jeff, full rated torque at lower than rated motor RPM = less than
rated HP. When using the variable pulley and back gear, you can
deliver full rated motor power (less transmission losses) to the
spindle at low RPM since the motor is running at the rated RPM.

I decided a VFD wasn't worth it on my Bridgeport even though I use
them on other machines. I wanted full power at low RPM. To get this,
I would still need to change the variable pulley and software
wouldn't have any idea where it was set. This still leaves the burden
of setting proper RPM on the operator.

The only reason upside I ca see to using a VFD is to get higher
spindle speeds. However, this means running all the pulleys,
bearings, etc. faster. I'm not sure how well balanced the pulleys are
and what RPM they are rated for. It's not something I wanted to do as
an exploding cast iron pulley is something I don't want to be around.

~petev

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "cnczeus" <lumen@c...> wrote:
> Most VFD's have a parameter for setting the drives profile to
> constant torque. This setting can draw up to 80% of full motor load
> and provides 100% rated torque down to about 10 RPM.The problem now
> is that at 10 RPM the motors fans do not provide the cooling
required
> by an 80% full load condition. Even though this has never caused me
> any problems or even any motor heating for brief operation,
extended
> operation points to a problem. Bridgeport's also have the low range
> back gear to handle severe loads at low RPM so a single belt speed
of
> about 2000 RPM @ 50HZ is what I prefer. This allows for the higher
> top end speeds you will wish you had.
>
> Jeff
>
> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "john_glynn57"
> <john_glynn57@y...> wrote:
> > Thanks Vavaroutsos and Lee,
> > My Understanding, at the moment, is this and I should proceed
as
> > follows:
> > 1. The inverter route is the way to go.
> > 2. I should setup the inverter to control the forward reverse
> > control.
> > 3. I should setup the inverter and the Bridgeport to run at the
low
> > speed of 1400 RPM and the inverter to deliver 1400 RPM at 50Hz.
> > 4. I sholud increase the motor speed by increasing the frequency
of
> > the inverter to >50 to simulate the higher speed of the
Bridgeport
> > and use the pulleys to actually gain the desired spindle speed at
> > the toolcutter end.
> > 5. By Carrying out 3&4 I should maintain the normal speed\torque
> > curce for the Motor.
> >
> > Please tell me if I am wrong.
> >
> > --- In CAD_CAM_EDM_DRO@yahoogroups.com, "vavaroutsos" <pete@v...>
> > wrote:
> > > If you don't use the variable speed pulley, you are going to
> loose
> > > spindle power at low RPM. The pulley provides about a 9:1 ratio
> > > between slowest/fastest settings. The motor is 4 pole 1800RPM
so
> > you
> > > could probably drive it safely to 3600RPM or a bit more. This
> only
> > > gives you a 2:1 ratio in the constant HP area of the curve.
This
> > > means the lower RPM will have to come at lower than 1800RPM
which
> > > will be in the constant torque area of the curve with
diminishing
> > HP.
> > >
> > > ~petev
> > >
> > > --- In CAD_CAM_EDM_DRO@yahoogroups.com, "Lee Studley"
> > > <indigo_red@q...> wrote:
> > > > In parallel to John's question, I'd like to know about
setting
> > the
> > > > spindle/motor ratio on my varispeed BP also, so that I can
> > control
> > > > the speed via the VFD. Does anyone have experience doing
this?
> > Any
> > > > caveats?
> > > > -Lee
> > > >
> > > > --- In CAD_CAM_EDM_DRO@yahoogroups.com, "Lee Studley"
> > > > <indigo_red@q...> wrote:
> > > > > VFD's are great!!
> > > > > I think most VFD's have reversing builtin(?). Having a
switch
> > > > break
> > > > > connections from the VFD to the motor doens't sound good to
> > me. If
> > > > > you want to keep the mechanics of the original Fwd/Rev
> switch,
> > I
> > > > > would suggest wiring it as a switch to control the VFD's
> > external
> > > > > fwd/rev option if it can be done as an external control.
> > > > >
> > > > > -Lee JMO-ICBW:-)
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > > > --- In CAD_CAM_EDM_DRO@yahoogroups.com, "john_glynn57"
> > > > > <john_glynn57@y...> wrote:
> > > > > > I have just taken delivery of my own Bridgeport mill and
> > want
> > > to
> > > > > > know which is the best option for powering the machine :
an
> > > > > inverter
> > > > > > or a converter.
> > > > > > My research to date suggests that a Hitachi L100 inverter
> is
> > > the
> > > > > way
> > > > > > to go however I want to question this as follows:
> > > > > > 1. I can run a dedicated 20A or 30A supply to the machine
> > which
> > > > > > should be able to handle the startup current demand of a
> > > > converter.
> > > > > > 2. If I use a converter I can use all the original
> > Bridgeport
> > > > > > systems without mosification ie Bridgeport speed
> > > control,forward
> > > > > and
> > > > > > reverse,3phase coolant pump and shaping unit which is
> > attached
> > > > to
> > > > > > the machine.
> > > > > >
> > > > > > My plan is to circumvent the original Bridgeport wiring
and
> > > > drive
> > > > > > the Main motor(s) directly from the hitachi unit and
> setting
> > > the
> > > > > > motor speed at the low speed of 1400 and not using the
> > valiable
> > > > > > speed control of the machine at all. The hitachi will
give
> > me
> > > > > speed
> > > > > > control by varying the frequency however I do intend to
use
> > the
> > > > > > original forward reverse switch. In addition I plan to
> > replace
> > > > the
> > > > > > coolant motor with a single phase model.
> > > > > >
> > > > > > Am I doing the right thing.