Re: [CAD_CAM_EDM_DRO] RE: Rong Fu RF 45 vs RF 31 CNC - VDF Spindle

I use a Mitsubishi VDF controller on a 2HP Bench Mill. The machine is
belted for a mediun speed speed and the spindle is controlled using the
VDF Controller. The Controller input is 220VAC Single Phase and the
output is 220VAC Three Phase, the phase conversion is not done with
rotary converters or other smoke and mirror technology that I have
employed in the past.. Since the frequency must be output at rates other
than 60 Hz, the input voltage is rectified to DC and then Inverted to
the required output frequency, the voltage remains constant. From there
it is quite simple to phase shift 60 degrees and output the inverted AC
again adding the second leg. Do this one more time and you have true
Three Phase AC that may be of a better wave form than power from the
pole. Add to that controllable acc/dec frequency ramps and there isn't
much to not like.

The US made motor has a 1750 Base Speed which is obtained at 60 Hz. The
VDF can control the frequency to higher or lower rate by input from a
hand held keypad. We are currently producing 2000 small "widgets:" with
a three minutes cycle time (4 minute part to part). The spindle is
running continuously at 90 Hz (150% base speed) with no preformance
issues at all. Cuts are made on the side of a 1/2" carbide end mill -
1/4" to 1/2" depth of cut, 3/4" length of cut at 15ipm. Spindle Motor is
not noticeably warm after 8 hours compared to the stepper motors which
are HOT (I hate Stepper Motors).

On the low side, the torque at the spindle starts to fall off noticeably
at 10 HZ (175 motor RPMs). Depending upon the belt selection and
mechanical reduction range selected, this can be quite slow at the
cutter but it stills allows the spindle speed to be radically increased
without a belt change..

All in all I like it!! These units may be found quite cheap on eBay. A
1/2 HP unit that I noticed sold for less that $75USD recently .

gary

Alan Marconett wrote:

>Hi Andy,
>
>No, haven't tried that. 2HP is a big motor, I'd probably get a VFD for
>it instead, although maybe that requires a better motor?
>
>Alan KM6VV
>
>
>Rajasingham., A. "Indi" wrote:
>
>
>
>>Maybe I should back off on the 5th axis ! Perhaps the angle plate will
>>do most of what is needed.
>>Have you tried the PWM contrllers for speed control without changing
>>belts on the RF31 ?
>>Torque mus tbe pretty low at low revs.
>>Andy
>>
>>
>>-----Original Message-----
>>From: Alan Marconett [mailto:KM6VV@...]
>>Sent: Monday, November 29, 2004 12:39 PM
>>To: CAD_CAM_EDM_DRO@yahoogroups.com
>>Subject: Re: [CAD_CAM_EDM_DRO] RE: Rong Fu RF 45 vs RF 31 CNC - Help!
>>
>>
>>
>>Hi Andy,
>>
>>It seems the Taiwan machines are slightly better finished then the
>>mainland China machines.
>>
>>The square column (dovetail?) would be better then the RF31's ROUND
>>column.
>>
>>I prefer belts to gears, gears can break, and would be hard
>>(impossible?) to replace. Belts I can get anywhere.
>>
>>Tilt head CNC? That's a little more then the Rong Fu wants to do. A
>>good angle plate can take care of most of that. 5 axis? you're talking
>>
>>about a really expensive machine.
>>
>>I think I saw ENCO offering upgrade motors, but not cheap.
>>
>>I have the RF-31, but haven't CNC'd it yet due to funds.
>>
>>Alan KM6VV
>>
>>
>>
>
>
>
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