Re: [CAD_CAM_EDM_DRO] VFD? - Bridgeport retrofit questions

Hi Jeff,

I'll have a go at all your questions...

ja_erickson wrote:

>greetings all,
>
>can anyone help me with a few questions about vfd's for use with a
>bridgeport retrofit?
>
>1.) when considering a vfd for use with a 220 single phase supply
> and a 2hp std. bridgeport motor, what rating should be selected
> a 2hp or somewhat larger, say a 3hp vfd?
>

If your motor is 2HP just go with a 2HP drive if you are buying new. If
you are buying off of ebay, and a 3HP unit comes up at a good price, go
for it. You won't gain anything other than a lighter wallet if you
over-specify the VFD for a spindle application.

>
>2.) from what i have discovered, these vfd's will also handle
> the reversing of the motors direction. by using one of these
> will i completely eliminate the original bridgeport switchs?
>

I have 2 VFD's both have configurable I/O lines that can control
direction and speed. Both also have an analog input that will accept a
pot connection, so you can rotate the pot to select a speed or a 0-10V
DC signal to control speed. (10 V = top speed, 0V= very slow or
stopped). Both also have a pot on the front panel that allows you top
control speed. I have only ever used the high speed range on my mill so
direction has not been required but the VFD's have an input where a
1=fwd and a 0=rev. (1=5v or 24v and 0=0v red the manual!) As others
have mentioned, touching the switch while the VFD is on or the motor is
running is a sure way to harm the VFD permanently...

>3.) by using a vfd, how will the bridgeports "hi-low" range be
> switch selector be affected as this machine is a variable speed
> spindle?
>

I leave my spindle in high range and vary the VFD frequency to vary
spindle speed. I have chosen 75Hz as my highest freq. and this
translates to a spindle speed of about 4500 RPM. I have the vari-speed
dial set to about 3500. I still run the dial down to its lowest speed
when the machine is warming up and then return it to the 3500 posn for
use. If I turn it higher, the spindle noise increases and I find I
don't have enough torque - on a heavy cut, the speed drops significantly.

>
>4.) other than by a computer, how else is the speed of the spindle
> regulated after installing a vfd?
>

See above - speed can be controlled via I/O lines, a pot, or a 0-10V dc
signal. On some VFD's you can also control speed via a serial or
ethernet connection - with the right comms software.

>
>5.) when using a vfd, what spindle speeds can be achieved typically?
>

I have run my spindle up to about 5500 rpm but it was toooooooo noisy.
I don't think it is the spindle bearings, but all the mechanical bits
hanging off the drive train. There are two belts, a spline and many
gears etc., all making a racket.

>6.) do these units affect the motors torque? if they do how
> is that problem corrected?
>

The VFD can give the motor a bit more low speed torque (I think) by the
way it excite the fields, but it cannot replace the torque you can
achieve on low range at low speed. I find that for most of my work with
1/2 " or smaller mills (except roughing), my feed rates are totally
limited by my spindle speed, not the available torque.

>
>7.) when using a vfd, how would you position the belt.
>

See above.

>
>8.) generally, does most of the original bridgeport spindle control
> circuitry become extinct?
>

My mill is a BP clone. It didn't come with any serious "circuitry"
other than a contactor - which I removed when I fitted the VFD.

>
>thanks again
>jeff
>
>
>
>

You're welcome. You will already know (or will soon find out) that
VFD's come with fat operating manuals. Don't buy one unless you also
get the manual, or can download it from the vendors website. They are
almost impossible to configure without a manual... You must invest some
time to learn how to configure it correctly. Mostly, the defaults will
be fine but in some areas you need to change the parameters. I also
found that I needed a braking resistor to be able to stop the spindle in
4 seconds rather than the almost 10 seconds it takes normally. Not all
VFD's make it easy to add a braking resistor. FYI, I've had very good
results with the Automation Direct house brand and their tech support is
great!

Cheers, Peter