Magnet came loose

[klsmurf]

Hi all
I have a PM motor that I use for a hobby mill. It's been up and running for about a year and a half now with no problems. I look out the other morning, and it wasn't spinning when it should have been.

Visually there was no problem, so I bump started it and heard squeaking. Bearing I figured. Dropped the tower, grabbed the rotor and turned it slightly......klunk   humm! Pulled the motor off the mount and took it inside to pull the face off.



As you can see, there's a problem. The top magnet is stuck to the rotor and all kinds of dust.

Assuming there no damage to the rotor, could the magnet be reattached? I haven't pulled it completely out of the can yet to do a complete inspection, just don't know if it would be worth my effort.

[oztules]

No problem here....

Many times I have had to fix up clients drive motors in machinery from the same problem.

Just pull the magnet out, and clean up the steel shell with sand paper or whatever you fancy, and get it back to iron... not rust or old glue.

Clean up the magnet the same way (grinder steel brush works well for this)

When both surfaces are clean and dry, use ( I used Araldite slow.... not the five minute stuff) a good strong glue.... and glue it up... just like when they made it for you in the first place.



.....................oztules

[klsmurf]

Great, thanks Oztules. I'll have to pull it apart now. Never done it before with the intention of putting it back together.

[artv]

Hi Klsmurf,....that's an interesting looking winding, I've never seen anything like that......
Would it be asking too much for photos?......When you get it apart that is....
Or even a description of how it's wound....
Don't go out of your way ........just curious........thanks artv

[klsmurf]

Hey artv,   Don't have any other pics at the moment and as far as what kind of winding......no clue what it is called. I'm not a motor guy and most of the time electrically impaired. I'm sure one of the smart guys will tell us.

[klsmurf]

Update:

   Got the motor pulled apart, inspected and cleaned up. Brushes and bearings were fine. Little rust on the brush springs and oxidation on the aluminum end.

Had some 4 hour JB weld so I used it. Shimmed and clamped and it seemed to work. Put it all back together and it spins freely. It seemed to be stiffer than I remember, but it's been over a year since I've spun it by hand. Did some bench testing on it and it seemed ok, so I'll put it back in the air and hope for the best.

I will state that putting the long screws that hold the can together was a PITA. Never done this before so I was clueless as to a method. It had me more frustrated than a one armed wallpaper hanger. Why aren't these screws stainless or aluminum. It was at least 45 minutes to get these started.

[rossw]

I will state that putting the long screws that hold the can together was a PITA. Never done this before so I was clueless as to a method. It had me more frustrated than a one armed wallpaper hanger. Why aren't these screws stainless or aluminum. It was at least 45 minutes to get these started.

You're likely well practiced now.... but I'd like to offer a tip to all those who don't know it already...

When doing up bolts (and indeed most things "threaded") it can be very easy to get them either cross-threaded, or (particularly if it's in a soft material) just cut a new thread (which can only happen so many times before there's nothing left!)

Over time, I've learned that the best way to make sure a bolt "starts" properly is to apply a gentle pressure and turn it BACKWARDS. You will feel it "drop" as it goes past the end of the existing thread. Now turn forwards and you should have a perfect thread engagement, first time, every time.

As for getting long bolts to line up, I've never found a sure-fire way to do it. If they're not captive, the best I can offer is to hold the device going back together such that the bolt or rod you're inserting is as near as possible to vertical, and lower it in. Once you get close to where the thread SHOULD engage, slowly "wind" it in circles around where you hope the thread is, in increasing and decreasing circles until you "find" the post or surface. Use your fingers as eyes and visualise the surface. (Looking at it first so you know where ribs, lumps and bumps are in relation to the hole you want). Once you've found the hole, the backwards rotation (above) can help confirm you've got the right one.

One final tip.... never do the first bolt up tight. Do it up just enough to keep it in position. You may have to wiggle things to get subsequent bolts in. Once all are in place, do them up gently only, make sure all mating faces have, and only then do things up firmly. (Otherwise, it can be easy to do things up with a bend or twist - which can make bearings and bushes be out of alignment - making things stiff and increasing wear)

[klsmurf]

"You're likely well practiced now.... "


Very well practiced! Your turning backwards to seat advice is the best for not cross-threading. I've messed about with both brass and aluminum screws and it helps.

These screws fit in a recess on the top of the can, with less than a 1/4" to hold on to when they started in the threads. I used a locking needle nose pliers, but the magnets would still pull the ferrous screws sideways.

[tomw]

These screws fit in a recess on the top of the can, with less than a 1/4" to hold on to when they started in the threads. I used a locking needle nose pliers, but the magnets would still pull the ferrous screws sideways.

I wonder if a wrap of tape might help keep them centered against the pull?

Just popped into my head reading that.

I have used the back it up til it drops into the thread trick since I was a kid and one of my uncles showed it to me after I cross threaded a nut.

Tom

[rossw]

I have used the back it up til it drops into the thread trick since I was a kid and one of my uncles showed it to me after I cross threaded a nut.

You're from the generation that was shown and told how to do stuff by those that could and did, and were generally bright enough to listen when the tips were offered. Sadly there are less and less who still know, and seemingly very few young folk who actually get out, get their hands dirty and do stuff.

[tomw]

 Sadly there are less and less who still know, and seemingly very few young folk who actually get out, get their hands dirty and do stuff.

For those scared of dirt my trick is Nitrile Gloves. Disposable, very tactile and keep you from getting grungy.

I actually got them for handling cast lead bullets. Would hate to ruin my prime health status by absorbing a dose of lead to screw up my chromosomes.  I find them handy for other nasty chores like handling greasy parts.

Tom