Micro mill desperate help for a novice please

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

I really hope I don't need one of these

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

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.

pmdevlin said:

I really hope I don't need one of these

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

Click to expand...

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

pmdevlin said:

I really hope I don't need one of these

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

Click to expand...

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

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

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?

Click to expand...

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.

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

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

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.

DJP said:

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

Click to expand...

not realy depending of the magnet strenght of the motor

rleete said:

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

Click to expand...

Sounds right cheap and easy to replace
Eric

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?

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

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.

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

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.

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

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?

Click to expand...

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

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.

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.