Re: [CAD_CAM_EDM_DRO] Added a VFD to my CNC mill

Dan,
According to a pdf file that I have (from NEMA I believe), the max safe
speed of a 3600 rpm motor will be 7200 rpm (up to and including 5HP) If
you would like, I would be more than happy to mail the file to you.

I also have another file from a motor manufacturer that includes this
information:

"Maximum Safe Mechanical
Speed Limits
(does not imply constant
horsepower capability)
Motor @ 1800 rpm
Frame Direct Belted*
56-184 5400 2250
213-256 4200 2250
284-286 3600 2250
324-326 3600 2250
364-365 2700 2250
404-449 2700 2250
*Belted per NEMA MG1-14.41 (dated
1993)"

However, I cannot find reference to this information in the NEMA file
listed above:{( Also, nobody that I have talked with can tell me WHY the
belted rate is lower than the direct drive rate??? However, I will also be
glad to forward the contents of this pdf to you also if desired.

Based on what I gleaned from these two files, on my 60Hz motor, I limited
the speed on my RF31 to a max of 100 Hz. With the belting arrangement I
have (replaced the 17mm bore original pulley with a single 7/8") on the
new 3ph motor, I can achieve speeds of 111 to 2220 rpm with no additional
belt changes. Now having said this, there isn't much torque at 111 rpm and
I have stalled it a time or two at that speed. As a matter of fact, I also
had it kick out on overload due to the extremely low rpm of the motor and
lack of cooling:{(

Still, I think it was the next best investment to my machine shop since
adding the mill/drill. And as you say, no more belt changes. Another
feature of my VFD is that I was able to set it up to give direct RPM
reading on the panel and I never have gotten round-to building that tach I
bought from you:})




At 11:32 AM 10/27/02 -0800, you wrote:

> About a year ago I bought am Mitsubishi VFD for $238 on ebay. It
>came with a 190 page installation, setup and operation manual. I took a
>look at it and indeed it was a really nice inverter that would take
>single or three phase supply and would run the three phase motor on my
>enco mill. Most important was that it allowed for external manual
>control with a speed pot, Parameter Unit, (a fancy keypad and LCD
>display for programming the unit) and for setting various parameters)
>and last and most importantly it took a +5 analog signal from an
>external source for PC control. Well. I finally got around to connecting
>it to my machine. Wow! I am impressed. So far I am just using the
>parameter unit for changing speeds. It works like a dream and runs the 3
>phase motor much better than the Phase-o-matic inverter that I use to
>use.
>Most impressive is that you can program the acceleration and
>deceleration rates of the motor. Before my spindle would take for ever
>to coast to a stop. I would have to use the brake. Now I have it
>programmed to stop in 4 seconds.
>I am going to figure out how to use the analog signal from DeskwinNC to
>turn on and off my VFD and set the speed from computer via the G code. I
>think that would really be a nice to automatically turn on the spindle
>motor and set the speed via the program. So far I can heartily recommend
>the Mitsubishi FR200E series inverters. BTW I have been told these
>normally sell for around $800 but got mine New off ebay for a fraction
>of that. It sure is nice not to have to change pulleys all the time.
>Last I would like to know how to calculate the maximum safe speed that I
>can run the spindle at. I would think that the 3500 RPM 50 Hz motor
>would cause the spindle pulley to explode if run at 400 Hz.
>Dan

Bubba

OLDER THAN DIRT
Country Bubba
(Actually the inventor of Country and Bubba)

axtein@...
LaGrange, GA

http://ns1.dicomm.net/~axtein/dro


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