Converting to 3 ph with a VFD

[reabdet21]

I have a Rong FU RF31 and am interested in getting a 3 phase motor, 2HP and possibly a SJ200 Hitachi VFD. What speed motor would be recommended? I intend to drill and tap aluminum in the same operation by just reducing the speed. What would be the range of speeds if using a 1725 verses a 3450 motor? Leaving it at one belt configuration, what could be the range of speeds and how low can a VFD take the RPM? Also what rating on the VFD would be needed to run a 2 HP motor? I mainly work aluminum so would it be more cost effective to use a 1.5 HP motor if the VFD needs to be overrated? I will be using single phase input to the VFD. I know this is a lot of questions but I need a lot of help. Thanks for any responses.

[Bubba]

On my RF, I used a 2HP package from Dealers Electric. It is comprised of a 2HP VFD (FM100) and 2HP motor. I have found that I can get a speed range of about 300 to 3400 rpm out of the one belt setting (1800 rpm motor) over speeded to about 116 Hz.
I have had it to lower rpm, but there isn't enough torque to do anything. Matter of fact, I have had it down to about 10 rpm and with no load, it will trip out in a matter of minutes!
It has been running this way for a few years and I find it completely satisfactory. I don't ever run it above about 3500 rpm as the spindle gets quite warm after a period of time. Don't know for sure if it is due to the seal on the quill or the bearings. I have seen opinions on both.

Somewhere, I read the average "turn down" ratio is about 10:1 and my figures show that. So it doesn't matter if you use an 1800 and over speed it or if you use a 3600 at normal speed, your are still looking at about a 10:1 turndown! There are torque/HP tradeoffs for either type of installation. Look at the manual and you will have to make your own decision.
As for the rating of the VFD, "most" modern units are fully rated to about 3HP whether run from single or three phase. Again, check the data sheet and it will tell you.

By the way, next to cncing the machine, this was the best investment I made!

[reabdet21]

Thanks for the help. The comment on the low end torque tells me I should go with the 1725 motor. A couple of question on the Hitachi SJ200 Drive if anyone is using it. I see one pair of terminals is for remoting a reversing switch. Is that correct? Also, the panel can be removed from the unit and remoted with a cable connector. It is quite expensive but appears quite handy. Is that a special cable or can it be purchased elsewhere. Any comments on how anyone has set up the VFD would be appreciated. Thanks.

[Bubba]

I cannot respond to the relocation of the panel, but on mine; I use the remote pot. function for the speed control. The pot used is a ten turn one and this gives a much finer control over the speed setting. I can now be programed very easily to a very few rpm (I show rpm on the display) as opposed to several 10's of rpm using the panel pot.
I still use the original panel for controlling start, stop, direction (although, I can't remember the last time I actually used reverse)

[reabdet21]

I know it is not recommended but how well do regular 3 phase motors do with a VFD application verses an inverter duty motor? Have you used them with any degree of success? I see by the specs that inverter duty motors are usually capable of around 4000 RPMs.

[Al_The_Man]

I have installed VFD's on many older non-inverter motors and so far have not had any problems.
I have two mills in the shop which have the older pancake style 3ph motors circa 1980, they both run up to double their base speed of 1745.
Some of the things that classify a VFD rated motor are the wire insulation grade to withstand the high switching pulses, although I believe all motors built in the past 20yrs at least will have high grade enamel.
Balancing and bearings are the other two concerns.
I usually use a rule of thumb that 2 pole I never run above the base speed of 3600 and 4 pole I usually run double base speed up to 3600.
I usually figure than most motor manufacturers who build 2p & 4p motors are pretty much going to be of the same design as each other, apart from the pole issue of course.
The above applies to non-inverter motors, Inverter grade motors usually have a max speed as well as base speed on the label.
Al.

[reabdet21]

One other question. I am going to have to decide between going cnc with the RF31 or another route. What is a reasonable figure dollar wise in converteing my RF31? Are their steppers that are powerful enough to mount direct with no belts for the X and Y? Are the kits sold the best way to go?

I would also appreciate any comments on what would be needed to update the controls and software on a bridgeport with Heidenhain controls. I think it only moves one axis at a time so is another control board necessary? Thanks.