# Micro mill desperate help for a novice please



## pmdevlin (Dec 17, 2014)

Hi all, I will set the scene! I'm pretty new at model engineering, and need some desperate help. I don't even know if I am posting the correct place, mods please move if applicable.

I was today using my micro mill, low rpm, milling some plastic sheet, so no problems here. I bought this off a friend, a very talented engineer, and a regular on this forum, he passed away last year, so my predicament is that I cannot go back to him to talk about the mill he knew inside out. It had been modified to suit his disabilities, it is belt drive, and the control panel was moved away from the machine so he could reach it. I believe its a seig machine, they are the instructions he gave me with it, although it has no markings on it. All I can say is he only used good stuff!

So after a bit of use, the fuse in the control panel blew, I changed it, it blew again. I have inspected the motor, taken it apart, all is good, no binding, brushes good, no signs of excessive heat,. all windings seem to be ok. The connecting block between the control panel and machine is good. Reassembled, fuse blew again.

So, with control panel disconnected from the motor, I can turn on, and turn up potentiometer, nothing is amiss. When connected to the motor, the motor immediately spins up with the potentiometer in the off position, and the fuse blows. I assume with potentiometer in off position, motor should not spin up?

I have inspected inside the control unit, all appears to be fine, and no smell of electrical death! I am now at a complete loss as I have absolutely no knowledge of how the control panel works, what to test, how to test, and what to do now please help! I am thinking the control panel is faulty, as its been modified the manufacturer will be no help, can anybody suggest a repairer or is the mill now finished!

Many thanks

Paul


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## pmdevlin (Dec 17, 2014)

I really hope I don't need one of these

http://www.axminster.co.uk/axminster-sieg-su1-power-feed


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## TorontoBuilder (Dec 17, 2014)

Hi Paul,

Two things I'd do... the first is test the motor windings with a multi-meter to determine there is no short. The second is to measure the amps while using the mill... use a plug-in wall outlet meter. Everything else inside is all integrated circuitry and I wouldnt know how to test it.

Although you say you're milling plastic at low rpm I'd guess that it could be a case of overloading the motor and taking too big a cut. Especially since the mill has been functional in the past.

I blew the fuse the first time I used my micromill having been used to full sized mill's ability to take big bites. Locating the proper sized replacement fuse was so annoying I decided to replace the fuse holder with a circuit breaker instead. It cost me all of 3 bucks at my local electronics store.


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## canadianhorsepower (Dec 17, 2014)

pmdevlin said:


> I really hope I don't need one of these
> 
> http://www.axminster.co.uk/axminster-sieg-su1-power-feed


 
 Can you post a few pictures of the inside of the controler it
 would help to ID the parts


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## velocette (Dec 17, 2014)

pmdevlin said:


> I really hope I don't need one of these
> 
> http://www.axminster.co.uk/axminster-sieg-su1-power-feed



Hi Your photos are of the main drive motor and the photo of the proposed replacement control is for the table power feed. 

Better deal Ex USA @ http://www.littlemachineshop.com/products/product_view.php?ProductID=4211 
For a table power feed

I Can recommend this site for parts supply to New Zealand. Delivery charges are a bit painful  but still good value for money

Try this site for spares for the main motor.

http://www.arceurotrade.co.uk/Catalogue/Machine-Spares/X1-Mill-Spares

Scroll down to control boards and compare yours.
An E-Mail  to Ketan for more info will help get you running again

I have no connection to this site I only know of the excellent reputation from other forums

Eric


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## pmdevlin (Dec 17, 2014)

Thanks chaps, I have used arceuro before, and they are UK. I have a test for the motor to try later, looks like that pic of the power feed is something entirely different! my bad!

 I will photo control  board as soon as I can

 Thanks


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## tornitore45 (Dec 17, 2014)

> When connected to the motor, the motor immediately spins up with the  potentiometer in the off position, and the fuse blows. I assume with  potentiometer in off position, motor should not spin up?



There is a 97% chance that there is noting wrong with the motor.
The fact that the controller does not "obey" the pot control and still runs the motor with the pot at OFF suggest the problem is in the controller and not the motor.

The controller is usually some sort of switch mode converter.  The fact that everything seems OK with the motor disconnected points to a series element between the rectifier output and the motor.  Most likely the switching transistor is shorted. It can be tested and replaced unless there is some collateral damage.

As a general note, power electronic greatest enemy is heat.  The power transistors are often heat-sinked with smallest heatsink they can get away.
The first thing I did to my X3 mill was to add a muffin fan just after the main switch, makes the heatsink virtually 3 times as big and all other stuff run cooler.


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## pmdevlin (Dec 17, 2014)

Thanks for the time taken responding, its greatly appreciated. I have just tried a couple of basic tests which might help more experienced people think of solutions.

I connected the motor up to 12v dc (don't know if its a dc or ac motor, I am assuming its dc) The motor did not run, but when moving the shaft by hand, I could feel some "resistance" which went if the 12v supply was disconnected. I stripped the motor again, and visually inspected under LED magnifier, I cannot see any evidence of overheating, seizure of bad windings.

I then connected the control unit to a 60w test light in place of the motor. Turned it on, expecting a potential fire risk! The bulb illuminated. I turned on the potentiometer, and turned up through the rpm range, the bulb light was constant. This was pleasing at first, as I thought the control board was working ok, but, should the bulb be illuminated when the rpm potentiometer is off, or am I being stupid. No way can I buy a new control unit, and a motor, so if anyone can think of anything I can try please keep the info coming

Paul


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## rleete (Dec 17, 2014)

I had similar problems with a micro mill.  Replacing the speed control pot solved everything.


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## DJP (Dec 17, 2014)

On my mini mill I need about 60 VDC to make it run. I wired mine with external connections for the day when the controller board dies in the middle of a project. I can feed 60 VDC directly to the motor to finish the job.

If the shaft is not seized the motor should rotate a little at 12 VDC.


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## canadianhorsepower (Dec 17, 2014)

DJP said:


> If the shaft is not seized the motor should rotate a little at 12 VDC.


 
 not realy depending of the magnet strenght of the motor


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## velocette (Dec 17, 2014)

rleete said:


> I had similar problems with a micro mill.  Replacing the speed control pot solved everything.



Sounds right cheap and easy to replace 
Eric


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## /// (Dec 18, 2014)

Hi Paul, I also believe your motor is OK and the fault lies with the controller. 12VDC is not likely enough to turn the motor over.
The fact that the lamp is illuminated with the pot in the off position, and that the brightness does not vary with the movement of the pot, strengthens the case against the controller.
Whether it is a fault with the pot itself or one of the other components on the controller board I'm not able to say.
Do you know anyone nearby with electronics experience and test gear that may be able to look at the controller for you?


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## pmdevlin (Dec 18, 2014)

dear all, 

 By "controller pot" do you mean the complete unit, or a component within the unit, are we talking about the potentiometer that controls the rpm?

 Motor shaft is very nice and smooth, I believe the spec is up to 180v dc, so maybe 12v just isn't enough to make it spin? So maybe have a punt with this
 SX1-124 Potentiometer (scroll down, I will have to establish which board I have) 
http://www.arceurotrade.co.uk/Catalogue/Machine-Spares/Super-X1-Spares

 While I am at it, instead of fiddly glass fuses, that I might keep popping until the unlit is fixed, is it possible to fit something like this

http://www.ebay.co.uk/itm/ABB-S201-...I_CircuitBreakers_RL&var=&hash=item4acf22ff18

 I don't know what the type and poles mean though?

 Don't know anybody with electronics experience, will have to ask about if it comes to that

 Paul


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## /// (Dec 18, 2014)

Hi Paul,
'pot' is just shortform for potentiometer.
I would definitely try a replacement pot first, cheap option.

Forget the circuit breaker, these are not suitable replacement for fast acting fuses.


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## pmdevlin (Dec 18, 2014)

I have found a local electronics engineer, as I am back in work tomorrow right up to Christmas time will be very limited, so I have dropped off the control unit and motor for testing. It might go a bit quiet now, Ill be back when I have some answers, hopefully!

 Paul


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## rleete (Dec 18, 2014)

BTW, I bought parts from Little Machine Shop.  Probably not the cheapest place, but they knew exactly what part and had it in stock.

Be sure to label the wires as you unsolder them so you can wire in the new one the same way.


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## TorontoBuilder (Dec 18, 2014)

pmdevlin said:


> dear all,
> 
> While I am at it, instead of fiddly glass fuses, that I might keep popping until the unlit is fixed, is it possible to fit something like this
> 
> ...



No, use a panel mount push to reset circuit breaker of the correct amperage.. like this:





It should be a direct replacement for the fuse holder in the front panel... you'd use the same two wires attached to the fuse holder. Just attach them to the circuit breaker instead using spade connectors


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## /// (Dec 18, 2014)

A circuit breaker could possibly be used but are more complicated than you might think.
They typically do not trip at their rated current instantly, sometimes they take many minutes to trip at the rated current(a thermal trip). The ABB S201 linked to above was close to half an hour at the rated current. Often they will not trip quickly(electromechanical trip) until the current reaches 5 or 10 times or even more of the rated current.
A typical quick blow fuses by contrast will fuse in around 1/10th second at only double the rated current, or 1/100th of a second at three times. 
Substituting a 2A quick blow fuse with a 2A circuit breaker could provide no protection at all.
Replacing the 10 cent fuses every now and then isn't really that difficult, I've never had to do it in the decade I've had my machines.
I'm not saying don't do it, but don't do it blindly.  Study the product data sheet and trip curves carefully.


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## tornitore45 (Dec 18, 2014)

The fuse main purpose is to avoid a fire when something fail.  The energy that a fuse deliver to the load before it fuses is often capable to create more damage when repeated power up on fault are made.

People that fix power electronic avoid as much as possible multiple fuse intervention, and go to lengths to diagnose the problem.

If you have somebody that is versed in electronic take advantage of him before crating more damage with repeated power up.

In my experience 8 times out of 10 a new fuse does not fix the problem because fuses are sized to stand the worst case with ample margin, and when they go is for a reason.


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## TorontoBuilder (Dec 19, 2014)

/// said:


> A circuit breaker could possibly be used but are more complicated than you might think.
> They typically do not trip at their rated current instantly, sometimes they take many minutes to trip at the rated current(a thermal trip). The ABB S201 linked to above was close to half an hour at the rated current. Often they will not trip quickly(electromechanical trip) until the current reaches 5 or 10 times or even more of the rated current.
> A typical quick blow fuses by contrast will fuse in around 1/10th second at only double the rated current, or 1/100th of a second at three times.
> Substituting a 2A quick blow fuse with a 2A circuit breaker could provide no protection at all.
> ...



Yes Simon, you are correct, however I wasnt specifying a specific circuit breaker merely illustrating the type. As always read product specs, there are plenty of fast trip circuit breakers available, if you have a electronics store close buy versus buying on the net they can help you make the correct selection. 

the fuse for my mill was a special order shorter than normal product... I dont know about you but not being retired, I only have specific times I can machine anything, so equipment needs to work when I get to it.


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## /// (Dec 19, 2014)

Sorry for the misunderstanding TB, I was not having a jab at you per se, just providing a little extra info and a warning for Paul if he does choose to take this route. My main focus was on the ABB product linked to, which is definitely not suitable for this application.


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## TorontoBuilder (Dec 20, 2014)

No problem Simon... I appreciate that you wanted to add more info, since circuit breakers are definitely a different animal than fuses resulting in circuit breaker selection well below that of the fast blow fuse rating.


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## pmdevlin (Dec 30, 2014)

well I'm in  a mess now, don't know what to do. The motor has been tested and reported to be burnt out. I took the motor apart before giving in to be tested, and could not see any evidence of this. The guy has connected up to 110v ac to test it, on the basis that the motor has a big spec sticker on it, and it does actually say 240v ac, however, on the arc euro site, the replacement motor says its a dc??????
 He says the motor ran for a very short period, then gave up, and a possible short was causing the fuses to blow and the motor to spin up without potentiometer input. I'm confused? I thought it was a DC motor, so why on the big sticker on the can it does clearly say its AC?
 So no further on really, except now I need a motor, and might still need a control board, anybody got any recommendations for a direct fit motor other than a massively expensive £88 from arc euro, and that might not even be the fix!


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## Wizard69 (Dec 30, 2014)

pmdevlin said:


> well I'm in  a mess now, don't know what to do. The motor has been tested and reported to be burnt out. I took the motor apart before giving in to be tested, and could not see any evidence of this. The guy has connected up to 110v ac to test it, on the basis that the motor has a big spec sticker on it, and it does actually say 240v ac, however, on the arc euro site, the replacement motor says its a dc??????


Don't [/quote] me on this but I believe that the motors on these machines are actually universal motors.   That is they can be run on either AC or DC.   The controller feeds the motor DC voltage.  


> He says the motor ran for a very short period, then gave up, and a possible short was causing the fuses to blow and the motor to spin up without potentiometer input. I'm confused? I thought it was a DC motor, so why on the big sticker on the can it does clearly say its AC?


Motors will some times do that if the fuse doesn't trip fast enough.  


> So no further on really, except now I need a motor, and might still need a control board, anybody got any recommendations for a direct fit motor other than a massively expensive £88 from arc euro, and that might not even be the fix!




This is up to you really, the Chinese motors aren't all that reliable so it might pay to look into a real DC motor.    Personally I'd out a better quality motor on the machine.   The problem is they won't be cheap if you go industrial quality.  You could also look into an AC 3 phase motor and VFD but I'm not sure about space on this machine.   Either approach may require some fabrication effort.  

The other gotcha here is that sometimes a bad motor, one that is shorted, can blow out the drive.   Something to consider because you could find yourself replacing both the motor and the drive anyways.


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## zebra7493 (Dec 30, 2014)

Right....the motor is ac or dc. 110v applied directly should make it run. 
Try that first.
If its labelled 240v you should be safe up to that voltage AC. I think up to 180 ish DC.
Try the controller with a 60w (or similar) light bulb connected instead of the motor.

If the motor runs at top speed when connected to the controller then there is a problem with the speed control pcb or possibly the pot.

I have repaired these pcbs before and the fault could be the speed control pot  or any of the semiconductors. There are some little transistors which are involved in speed control and some large thyristors(?) on heatsink. 
Any electronics person should be able to test the thyristors (if they are short circuit they are dead.)

I have a circuit somewhere of one of the versions of PCB which I may be able to find. A photo of the component side of your PCB would be useful.

Do you have a multimeter?


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## pmdevlin (Dec 31, 2014)

I'll be collecting the motor and controller shortly. I am told the motor has emitted the magic smoke, and made all sorts of horrible crackling noises, so, if it was ok before it went to be tested, it certainly isn't now. I don't have a way to determine if it was faulty beforehand, the fuse in the controller could have been blowing prior to the smoke, I bet he tested without any circuit breaker, or he has fed ac when its  a dc motor, I keep going back to the fact there is a large spec sheet on the motor, and it does say 240v ac on it, is that referring to the control panel? I will have difficulty laying the blame for the motor expiring on him with that sticker on it, and I'm no further on with knowing if the controller board or pot are actually faulty. Replacing bot motor and controller is out of budget, second hand, I doubt the machine is worth it.

 I'll post up a pic later with motor spec, 

 Zebra, before I gave it in, I connected a 60w bulb to the output of the controller, with pot in off position, the bulb was very bright, turning the pot up made no difference to the brightness, and the glass fuse didn't blow. I have a multimeter, but it fills me with dread!! No idea what it does, its just a little cheapo one, very confusing, looks like this is going to be a dead machine for some time:fan:


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## pmdevlin (Dec 31, 2014)

motor has been collected, controller later, as he has not yet checked the output from controller, I want him to do this to satisfy me its ac or dc, and the pot is doing something!. Big sticker says AC240, a small sticker on rear says dc240v


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## pmdevlin (Dec 31, 2014)

quick google of the motor serial numbers, and I have found exactly same for sale at arc euro trade, and its a dc motor so he has fried it by lumping ac into it. The big sticker js the mill spec, not motor, I feel so stupid now!

 So its a trip back later, and to argue the point that he should have known, and read the sticker on the reverse, lets face it, he is the expert, not me, that's why I took it in the first place


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## zebra7493 (Dec 31, 2014)

If the bulb came on at full brightness then I either the Devices (thyristors or in this case FETs I think) which control the motor are short circuit so basically on all the time OR possibly the pot which controls the speed could be open circuit. 


I have posted a controller circuit at
http://sx-innovates.co.uk/SiegX2circuitboard.pdf
Its for the X2 mill but should be similar.

Your controller looks to me like its a lathe controller as it has reverse. I think they use the same boards for both.
The motors are probably AC/DC. As are things like mains powered drills. So AC mains shouldn't kill it. 
Motors can behave oddly if the windings have shorted turns of insulation breaking down to earth. Sometimes the will run a bit until warm or just draw too much current whilst still seeming to work.


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## DJP (Dec 31, 2014)

I would look at this failure as an opportunity. I was never happy with the speed control circuit on my mini mill and the internal plastic gears looked like a liability as well. With my set of end mill cutters the speed that I use does not change very much so I could do without the variable speed feature. Perhaps just a hi/med/lo option would be enough and a simple switch will do that very reliably.

Consider any new motor that will fit and make a simple controller for the voltage that the motor requires. I like the implementations where gears are removed and the mini mill is belt driven. That would be a robust and lasting machine in my opinion.

A fried controller board and burnt out motor are an opportunity to make the mill better. That's how I would approach this and for sure I wouldn't buy replacement parts to end up with the same weaknesses and liabilities.

My thoughts for your consideration.


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## pmdevlin (Jan 4, 2015)

I don't really use the variable speed either, just rely on med, and low, so it is a consideration if the controller is finished.

 I am picking it up from the "expert" in a few days, he has agreed, if I can prove its a dc motor he will take responsibility, not hard to do as it has a sticker on the can. Although I have twice provided the link for direct replacement and spec on the arc euro site, he seems reluctant to actually do any investigation. Strange, if he had spent 10 minutes doing this in the first place !:wall:


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## zebra7493 (Jan 4, 2015)

If you have all your parts back, a simple test of your controller.....
Connect up with the bulb instead of the motor. Get your multimeter out and set to DC 20v range and check the voltages at the pot.
One end should be 0v,  the other end 12v and the middle terminal should vary as you turn the knob. You can check at the terminals on the PCB or at the actual pot. 
If your pot also has a switch don't confuse the switch terminals with the variable resistor terminals. The variable resistor terminals are usually the 3 in a row on the side and the switch terminals normally are on the back of the pot.

If the voltage on the middle terminal varies as you turn the knob the pot is ok. If the voltage does not vary then the pot is bad. Replacement from a electronic component supplier is normally less than a pound (dollar if you are in the US)


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## pmdevlin (Jan 5, 2015)

picking up controller tomorrow, thanks for advise!


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## xpylonracer (Jan 5, 2015)

Hi, don't forget there were 2 stickers on the motor body and one of them stated 50-60 Hz, that means it will run with AC.
Hope the replacement controller and motor work for you.
Emgee


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## velocette (Jan 5, 2015)

xpylonracer said:


> Hi, don't forget there were 2 stickers on the motor body and one of them stated 50-60 Hz, that means it will run with AC.
> Hope the replacement controller and motor work for you.
> Emgee


 A bit late with this errant info it has already been established that the motor is DC and the the control is an AC to DC speed control unit.
Read the post Immediately after the one with the attached photos of the motor.

Eric


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## zebra7493 (Jan 6, 2015)

I think you are all on a bit of a wild goose chase with the AC or DC motor.
Most motors with brushes are AC or DC (things like power drills and vacuum cleaners) They have a stationary field winding and brushes which connect via the segmented commutator to the moving rotor windings. 
I could explain the theory If anyone is really interested.

It seems to me that the most likely fault progression was the motor suffered an insulation breakdown resulting in a few shorted turns making it draw more current which blew fuses.
When put on the bench for a test run without the same size fuse protecting it the shorted turns became a 'hot spot' causing more shorted turns etc until it failed completely. 

If you could identify which field winding had failed it is quite possible to rewind it by hand. 
I have done it quite a few times by simply cutting the winding off, weighing it and winding on the same weight of the same thickness of wire. One needs to take care with the direction of the winding and the connections of the start and end but its not that difficult.


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## BaronJ (Jan 6, 2015)

zebra7493 said:


> I think you are all on a bit of a wild goose chase with the AC or DC motor.
> Most motors with brushes are AC or DC (things like power drills and vacuum cleaners) They have a stationary field winding and brushes which connect via the segmented commutator to the moving rotor windings.
> I could explain the theory If anyone is really interested.



If it was a universal motor, I would agree with you.  In this case the motor is a "Permag" type.  This motor has a permanent magnet field consisting of two magnets where the field winding would usually be.  It will only work with DC.



> It seems to me that the most likely fault progression was the motor suffered an insulation breakdown resulting in a few shorted turns making it draw more current which blew fuses.
> When put on the bench for a test run without the same size fuse protecting it the shorted turns became a 'hot spot' causing more shorted turns etc until it failed completely.
> 
> If you could identify which field winding had failed it is quite possible to rewind it by hand.
> I have done it quite a few times by simply cutting the winding off, weighing it and winding on the same weight of the same thickness of wire. One needs to take care with the direction of the winding and the connections of the start and end but its not that difficult.



Yes this technique works well to replace a damaged winding as long as it is one that is on top and not buried beneath others, in which case the whole armature has to be rewound, along with re-lacquering and crimping to the commutator bars.  On small motors it's hardly worth doing.  Field windings are relatively easy.


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## xpylonracer (Jan 6, 2015)

Hi Eric
Yes I should have read the message you referred to but see it is now a PM motor.

Did you read about the primary belt drive for that Velo ?
Emgee


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## zebra7493 (Jan 7, 2015)

Hi Baron
Permag? I'll take your word for it. Mine looks the same and has a field winding.

Armature windings are difficult because they are normally buried on one side. That's why I only suggested it for the field winding.


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## /// (Jan 7, 2015)

zebra7493 said:


> Mine looks the same and has a field winding.


Interesting. I've just inspected my two Sieg branded machines and they're both definitely permanent magnet motors.


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## BaronJ (Jan 7, 2015)

zebra7493 said:


> Hi Baron
> Permag? I'll take your word for it. Mine looks the same and has a field winding.
> 
> Armature windings are difficult because they are normally buried on one side. That's why I only suggested it for the field winding.



Some of these motors do have field windings and I agree it is not always obvious without taking the end plate off.  I remember years ago coming across a permag motor for the first time.  It was fitted to a Philips washing machine.  At that time they were so new that in order to get a new one you had to return the old one, and you couldn't take them apart either.  There were four long pins running the full length of the casing, dome heads on one end and a funny squeezed crimp on the other.

The excuse or reason given for this construction was that if the armature was removed it would damage the magnets by reducing their strength.

As far as armatures go I've rewound a few !  It's not a job that I relish even with preformed coils and pre-made replacement commutators.


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## Wizard69 (Jan 8, 2015)

zebra7493 said:


> Hi Baron
> Permag? I'll take your word for it. Mine looks the same and has a field winding.
> 
> Armature windings are difficult because they are normally buried on one side. That's why I only suggested it for the field winding.




I can't say for sure but I was under the impression that the motors on these machines are in fact universal motors.    The motor is run off a DC controller.    Of course it is possible that the motor wound stator DC motor.  However with the motors stamped for both AC and DC that is unlikely.


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## /// (Jan 8, 2015)

Wizard69 said:


> However with the motors stamped for both AC and DC that is unlikely.


It isn't though, one sticker is for the individual motor and only mentions DC-230V on it, the other label is for the mill as a unit.


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## BaronJ (Jan 8, 2015)

Wizard69 said:


> I can't say for sure but I was under the impression that the motors on these machines are in fact universal motors.    The motor is run off a DC controller.



"Of course it is possible that the motor wound stator DC motor."

I'm not sure what you mean here ?




> However with the motors stamped for both AC and DC that is unlikely.


One of the major problems with universal motors is that without some form of loading they will theoretically run away with themselves at very high speeds.  Indeed I've seen a number of motors that have destroyed themselves because the unloaded speed has caused the commutator to loose segments.

A permag motor will only run on DC because of the permanent magnet field, and the speed is controlled by the voltage that is applied to the armature and ultimately by the amount of current that can be passed through the windings before they burn out.

Because of the inductance of the armature windings you can apply a fixed DC voltage, but if you rapidly switch this voltage on and off, you can control the average voltage seen by the motor and thus it's speed.  This is basically what the controller is doing when you turn the speed control knob.


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## zebra7493 (Jan 10, 2015)

I came across this page which may be useful for anyone having controller troubles with the mills of lathes
http://www.littlemachineshop.com/Reference/DriveTroubleshooting.pdf


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## pmdevlin (Jan 10, 2015)

progress so far, I have the motor back in my possession. Whilst the guy who was the so called expert agreed he had misread the label and tested on 110v ac, when there was another sticker saying 230dc on it, he wanted to test again (why he didn't do this 3 weeks ago baffles me, it would have saved all these problems!) saying if he was replacing the motor he wanted to be sure it was infact burnt out. He had run it for seconds, it had smoked. So, after testing on 60v dc for a period of time, the motor showed no signs of failure, it was on a variable supply, it ran on tick over, and then up to 60v dc continuously, so I think it seems ok. I have taken it apart, no signs of damage, no smell of death, so hopefully its ok when it runs again on the machine.

The control board has been sent to someone who graciously offered to repair (on another forum, uk based) He has the test equipment, and the knowledge. All things are pointing to the pot as the motor was trying to run once the control was turned on, even with the pot off, or a reparable component on the board, it has been explained, but I was totally lost with the explanation.

Thanks to all who have so far contributed, I will report back when I have the info about the controller.


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## pmdevlin (Jan 21, 2015)

controller came back, I was so grateful for the help, a mosfet was tested to be faulty and repaired. The controller was wired to a 60w bulb, and the pot altered the brightness, which was not happening before that repair, so all looked good. Connected all up last night, after a min or two, all was well, with variable speed, then a flash from the motor, and the original symptoms are back, blowing fuses, and the pot having no input, as soon as the controller is turned on, motor wants to run with pot turned off, so its back to square 1!
I did the bulb test again, its on real bright and pot does not alter brightness. I've ordered a couple of new mosfets, as I have been instructed how to change them, I'm thinking of getting a  new pot incase  that is faulty, just trying to take the cheapest way here!


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## Wizard69 (Jan 22, 2015)

pmdevlin said:


> controller came back, I was so grateful for the help, a mosfet was tested to be faulty and repaired. The controller was wired to a 60w bulb, and the pot altered the brightness, which was not happening before that repair, so all looked good. Connected all up last night, after a min or two, all was well, with variable speed, then a flash from the motor, and the original symptoms are back, blowing fuses, and the pot having no input, as soon as the controller is turned on, motor wants to run with pot turned off, so its back to square 1!
> I did the bulb test again, its on real bright and pot does not alter brightness. I've ordered a couple of new mosfets, as I have been instructed how to change them, I'm thinking of getting a  new pot incase  that is faulty, just trying to take the cheapest way here!




I really think you need a new motor.    These Chinese motors, at least a good portion of them, are known to be unreliable.   The fact that you saw a flash from the motor just seals the deal here, the motor is shorting.  If it was me I'd invest in a good American made motor.


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## pmdevlin (Jan 22, 2015)

looks like I will have to bite the bullet ion the very expensive motor then

boohoo!


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## DJP (Jan 22, 2015)

It does look like a short in the motor is causing the FET failure. Before you buy a new motor get yourself a really big diode at an electronic surplus store and rectify the line voltage to make DC for the motor. See if it will run well enough for your needs. The diodes that I am thinking of come with thick braided wire leads and threaded studs for mounting in a heat sink. They are probably rated at 300 amps and placing a few of them in series will reduce the voltage and speed of the motor. You won't have variable speed control but you may be able to use the machine.

Once the motor short becomes a serious recurring issue then buy a new motor.

My motor control board is acting strangely and I'm thinking of a simple and more robust solution as well. You might as well go first.


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## pmdevlin (Jan 23, 2015)

I fitted the new fet tonight, but, didn't realise that the screw holding the heatsink had to line up, so then had to remove the new fet and fit the spare. Whilst getting it off, I "could" have damaged the board, really don't know, because when I powered it up with a test light, all was well for a few minutes, then one leg of the fet sparked, and that was the end of that .
I possibley (likely) need a motor, and now need a board, its really not worth it, too expensive, and the board is out of stock anyway at the only place with one, arc euro trade.(uk)
I have to call it a day, and will consider selling the machine for parts/spares. Buying both parts is the only way I will be sure that its fixed, luckily the board was not fitted back inside the case when I did the test, otherwise I would not have seen the fet sparking.
I need to pack it up, and think long and hard, almost £200 to get it working again, I bet the machine isn't worth much mort than that.
Many thanks to all that contributed 
Paul


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## DJP (Jan 24, 2015)

It looks to me as if you have proven that the motor is OK if the controller failed while powering a lamp. The basics of the machine are still there and all that you need is a 60VDC source of power. Check out surplus electronics stores or perhaps a router speed control will work.

In my opinion the controller for the mini mill only has value as a quick stop circuit to save the plastic gears. Once you give that up there are options to making it a usable machine. My controller board has strange symptoms and I'm waiting for a total failure to change it to a simpler design.

You shouldn't give up just yet.


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## pmdevlin (Jan 24, 2015)

Thanks DJP for the time taken for previous post, although I can tell you wrote it in simple terms, unfortunately it was way beyond my understanding. With electronics, its turn it on, and expect it to work, although I have learnt a lot in this thread, and just found out you can damage a fet just by handling it wrong.

So, after sleeping on it, I decided to ring arc euro trade in UK, they are the only people who are showing original spares, and the machine originated from them a few years back, but not by me, it was my pals, and its a nice machine with some great accessories, long table, and spare short table, digital readout, rotary table, two vices, belt drive, so if broken for parts should fetch a few quid.

After discussing why I was chasing returned machines and second hand stuff, they suggested returning motor and controller, they would test in situ on machines, and report back. Its a fair charge for services, and at least I will confidently know if I need one, or both components, before I go spending money. The motor will now be tested at the correct voltage and speed

DJP maybe you are right, I don't need reverse as I don't use it, and its already belt driven, so there must be a cheaper motor alternative somewhere


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