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Hi,
First off this looks like a great place to be once I wrap my head around all of this. I must say it is all a bit overwhelming to begin with.
I have a real simple task and I am trying to figure out the cheapest way ot solve it.
I recently purchased a 3 phase vertical mill and I was planning on boot-strapping 3 phase from 220 fed into a 3 phase motor. Long story but it does work. While I was looking for a 3 phase motor the guy at the shop showed me how bad it was for the motor. Even though the guy who sold me the mill had powered a shop for 20 years this way I saw his point. I can explain the rest of it but I should get on with my question.
I am replacing the existing 3 phase motor with a 180 VDC motor and controller that will allow me speed control for the actual milling head. Now my issue is the power feed on the mill. It is also powered by three phase. It is a reversible 1700 rpm motor that basically drives a gear reduction system for the power feed. It is a flat plate mount that looks to be a standard size much like the servo or stepper motors. It is listed as a 1/4 hp motor. the switch on the front dictates forward or reverse and a set of switches stop the motor from feeding the table.
What is my best solution for driving this gear reduction system? servo or stepper? It needs to run at a constant speed and be able to be shut off with some type of limit switch. I looked at replacing the motor with a rev. AC motor but the mounting of the motor looked to be the issue, along with cost and rpm.
After typing this all out I am seriously reconsidering just going my original route and hope I don't trash my motors too bad with my poor mans three phase.
Any ideas?
Thanks in advance, Chris.
There are many instances here and elsewhere of RPC use, either home built or purchased already tuned, if building yourself, the tuning with capacitors is the key.
If you have already replaced the spindle motor with a DC motor then it may be better to look at stepper or other options for that small a motor.
By flat plate mount I assume you mean C face?
You can look for an equivalent stepper etc with the same NEMA size mount.
Al.
CNC, Mechatronics Integration and Custom Machine Design (Skype Avail).
“Logic will get you from A to B. Imagination will take you everywhere.”
Albert E.
Let me see if I can get a photo of it. The original motor is from Taiwan and it shows the type to be "TEE". flat face with 4 bolts.
SOMETIMES the 3ph input DC servo controlers can be run single phase. There is some derating of the power output, but that may be worth investigating.
This is what the cross feed motor looks like.
Before any decision I would drop the motor back and measure the flange, shaft and bolt pattern and also see how the shaft is attached.
Al.
CNC, Mechatronics Integration and Custom Machine Design (Skype Avail).
“Logic will get you from A to B. Imagination will take you everywhere.”
Albert E.
The motor is a 3 ph reversible constant speed motor. It has a fwd and rev switch on the front of the mill to control feed direction. The big gear box the motor is mounted too actually does the gear reduction for the speed. It has a handle to engage the gear drive once everything is turned on.
I figure there has to be a cheap effective way to input power to it and to provide direction control. And of course turn the motor off when it hits the limit switch.
Good point, maybe I can get that done this evening. That sight glass on the front of the motor tells me it might be some sort of wet spline.Originally Posted by Al_The_Man
This is looking more like a very detailed swap. Maybe I should just find a motor to make my poor mans 3 phase.
If it is 220v a small 1ph in, 3 phase out, VFD to control the existing motor is going to be the best way, you can either run it at 60hz if you want the original constant rpm, otherwise you also have the option of variable control.
Al.
CNC, Mechatronics Integration and Custom Machine Design (Skype Avail).
“Logic will get you from A to B. Imagination will take you everywhere.”
Albert E.
Ok, I will try to explain this without screwing it up. I saw this work and he said he had used this method for 20+ years. He also set up a guys shop this same way and it has run for 12 years. It does require a small motor to get the 3 phase motor running but then you turn on the 220 to the three phase and turn off the power to the small motor. I think it works on inducing a voltage in the windings of the third phase. He said the voltage on the non-powered leg runs from 106 to 130.
I found a diagram and erased the part he doesn't use. The diagram uses a series of capacitors to support the last phase. It is from Rotomasters | Rotary Phase Converters - 3 Phase Converter Specialsts
Last edited by cjsamples; 06-22-2011 at 08:04 PM.
Ideally you need to tune it to bring the 3rd phase up to ~220v.
Also you have to have some way to start the 3ph motor and get it up to speed ASAP.
Otherwise you blow the fuse or trip the breaker.
I prefer a start cap, rather than a 'pony' motor to bring the main motor up to speed.
This is one I made several years ago from the FRW- files in this directory.
metalworking.com - /dropbox/_1998_retired_files/
Al.
CNC, Mechatronics Integration and Custom Machine Design (Skype Avail).
“Logic will get you from A to B. Imagination will take you everywhere.”
Albert E.
He had this all wired into a panel. Flip on the 110 motor that was belt driving the 3 ph. Flip the switch(single throw/double pole) to power up the 3 phase, then shut the 110 motor off. The 110 motor was being back driven by the big motor but at that point it was not doing much.
This might be the cheapest and most time effective way to get my mill running. I haven't done the motor swap yet, just chased down the parts. He told me to look for a 5 hp motor for the mill, but I bet if I do the DC motor swap I can go much smaller on the motor for just the cross feed motor. It is only a 1/4 hp. Then I can work on getting the table to single phase later.
Thanks for all of your replies.
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