Mill motor question

[galland]

Hi guys,   Was wondering if any of you electrical specialists can help me with what ever happened yesterday. I have a Emco FB-2B milling machine which is a Chinese version of the original Austrian machine. Was taking a cut last night and suddenly the motor dropped from its normal speed to a crawl and I shut it down immediately. This motor always has ran hot after several minutes of milling but has always worked fine for many years now. I left it and came back later when it was cold and tried it again. Motor starts immediately but again will only crawl at a very low speed. I always assumed a motor was fine or dead and nothing in between. I know the switch has various electrical parts in it and was wondering if it is the problem and not the motor.    Gary

[Alyn Foundry]

Hi Gary.

From your photo I can see one Capacitor case, are there two?

The symptoms suggest either a faulty start capacitor or possibly the centrifugal switch has given up. This switch is inside the motor case.

It will be a process of elimination to put the problem right. If you have access to a Multimeter, you could remove the capacitor cover, desolder a wire from it and test it using the Ohms ( resistance ) setting. With older analog meters you'd see a flick of the needle ( good ) or a steady reading ( bad ) .

Before testing anything, disconnect the supply and discharge the capacitor

Cheers Graham.

[Jo]

I agree with Graham.

Looks like a single phase capacitor start/run motor. Look at the two capacitors (discharge them first) one will have gone, you need to replace it.

Running hot can be caused by the centrifugal switch not dropping out, which would have caused the cap to blow in the end..

Jo

[Admiral_dk]

I'm not saying that there is no capacitor - but there is none shown in the schematic over the switch and motor connection !!!!
The symbol that looks a bit like a capacitor is a poorly printed Ground symbol ..!.. drawn between the ground wire and the motor house / casing.

Is the mill belt driven ? - If so, remove the belt and try to turn the motor over by hand, so you can get an idea about the state of the bearings or other things preventing it from normal running. If that feels ok, try to start it without the belt and listen .... If this sounds normal, try to turn the driven belt wheel and feel again.

---- EDIT --- Ah - I see the black "box" on the side of the motor now .... and yes it is a common reason for motor problems on this type of motor .....
Best wishes and with a hope for a cheap recovery.

Per

[galland]

Thanks guys for the info. I will take the capacitor out and check it with a meter.    Gary

[Don1966]

A way to see if the centrifugal switch is not dropping out is to amp check it with an amp meter. The amps will be high. The can on the motor suggest it has a capacitor but could be just one which will be a start cap the motor starts so not the problem. If it has a second can capacitor which is oil filled this is the run capacitor this could be the one that’s short circuited and causing the motor to slow down. but if no second capacitor as Jo suggested the centrifugal switch could cause the motor to slow down And heat up fast if it doesn’t trip out.

Don

[petertha]

My mill is different but I had centrifugal switch issues which wreaked havoc on the capacitors. The motor ran fine for many months, then the problem appeared sporadically for a few starts, then capacitor went bang. Then I cleaned my shorts.

During the brief sporadic period when I powered the machine it almost sounded like the gears were grinding (mechanical). But it was actually more of an electrical cogging effect. Much head scratching & cap replacement & start/kickout switch diagnostics and.... Turns out the plastic cooling fan which resides on the motor shaft has a cheesy shaft retention system. So what was happening was the fan slowly drifted down the shaft over time to the extent it started impeding the centrifugal switch from extending, thus the start/run capacitors could not phase in & out. The points were just a teeny bit pitted & sooty but I cleaned them with a fine nail file pad. Set the fan with appropriate headroom, replaced the crappy screw with a real fastener that I could actually tighten, used a dot of blue Loctite & presto, happy milling again.

So as you disassemble, make some felt pen marks & snap a few pics because along the way as there could be some subtleties that are the difference between working & not working. Good luck!

[galland]

I pulled the one capacitor (the only one visible) and checked it with a meter and appeared to be ok. I pulled the end cover and fan off and found a sealed case so the other parts are apparently internal. Now for the fun part (Chinese workmanship). The photo shows that another cover is held on by the 4 screws and so I went to remove the nuts. You can see the left rear came off but as I turn the other 3 they all jammed on the shaft. Looking closer I saw all the ends are deformed and threads are screwed up. After each nuts turned several threads they all locked up and loosened the long studs. They apparently aren't screwed into the other end but pass through something and have nuts because now they will nut retighten either. What fun. So now I am scratching my head again. This mill still worked fine until 2 days ago but is 20 years old so probably no parts available.     Gary

[Jo]

Go to the other end of the motor and undo the bolts that secure the motor to the mill.

The worst that can happen is that you buy a new single phase motor which has the same shaft diameter and mounting arrangement and bolt it on. So it should be less than £100 very worst case.

What does the motor plate say?

Jo

[galland]

Well I pulled the motor and removed the other side and found out the long studs were actually Philips screws. I held the entire motor up to my grinder and ground off the 3 studs down to the nut (made it easy to unscrew them. I then pulled the top side off the motor expecting to see another capacitor and a switch like in the one photo I found on browsing motors. Mine was nothing like it with just a big hole once you pull the armature out. Don't have a clue how it functions.
I mentioned earlier I thought the capacitor was good. I put meter on smallest reading (200) and it jumps up pretty good but then falls rapidly to 6.1 each time. Is that good? I also am still wondering if its the magnetic switch that is causing the problem. I am showing a closer view of wiring diagram.    Gary

[galland]

Woops,  Meant to send one of the armature. Motor is fairly small and I don't think its a standard size so don't know if one can even be purchased. Roughly 8 1/2 inches long and 4 1/2 in Dia. Is rated 1/4th horse and 1.8 amps.    Gary

[Jo]

These are the plates that will tell us more about the motor, The diagram on the Yellow box is the Electrical wiring of the machine (maybe check your manual)

Motors are specified by shaft diameter, mounting arrangement, power, voltage and type.

Jo

[Alyn Foundry]

Good morning Gary.

During my time at Chester UK, a Far Eastern machine tool importers I learned that some of the electric motors fitted to machines were " specials " they had the habit of trying to get " a Quart from a Pint pot " !!

The circuit diagram pertains to the NVR, No Volt Release, an electromagnetic safety relay that ensures if the mains supply fails the motor won't run until you press the Green button.

A Capacitor consists, basically, of two metal plates ( foil ) separated by an insulant. Another way of testing them is to apply a DC voltage ( battery ) to the connections for a second or two. If the Capacitor ( holds ) this charge, by checking with a Voltmeter, then it might be good. The downside is that there still might be damage to the insulant that only appears at higher voltage. Don't directly connect it to the mains. That's another story.

The third, and final possibility, after cap and switch is that the " start " winding has got so hot its developed a short circuit ( shorted turns ) the nose is probably the best piece of test equipment here !!

Cheers Graham.

[galland]

Thanks again guys for all the help and suggestions. I would gladly buy a new motor and magnetic switch if I was able to find one. As I stated it is a somewhat unique motor and it attaches to the top cover of the 6 speed gearbox with 4 bolts. I mentioned mine is a emco knockoff and others were produced. I have included a photo of another one I considered back in the day. I even emailed the company I bought it from way back then (Blue Ridge out of Virginia) but they never even answered me back.     Gary

[Dan Rowe]

Normally the name plate will list the frame size but it is not there. Here is a link to a motor frame size chart.

http://www.esrmotors.com/Literature/References/ESR%20NEMA%20Chart%202011.pdf

Maybe you can find a matching motor.

I remember Blue Ridge I was looking at the Maximat line years ago.

Cheers Dan