rewinding a motor

I have a 5hp capacitor start motor from an older radial arm saw. The part is no longer available from the manufacturer. I had the motor
tested and was told that the starter winding is blown. The company that tested it would want $350. to rewind it. Neither that, nor a new saw is in my budget right now. They told me it cost a lot because it had to be done by hand.
I have two hands, a decent understanding of mechanical things and a lot of time. I know how to solder, but I have never done anything like rewinding a motor before.
Is it a folly to think that I might be able to rewind this motor myself and have it work?
Any suggestion of "How to" books I might look at?
tom
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Price seems about right, we would have charged a bit more (used to work in a re-wind shop). Smaller motors take just as much labor as larger ones, just different size wire. And tiny ones are hard to get your hands into to work. Then there is a big price shift at the large end when motors shift from using 'wire' and start using pre-formed 'bars' of copper.
One problem with doing this is you may have a hard time getting to the start winding without also pulling/replacing the run winding. So you may end up doing both before its all over.
With no data sheets, it's *extremely* important that when you disassemble and remove the old winding, you take very good notes. Make note of the exact wire gauge used. Exactly how many turns in each coil (concentric coils, common on single-phase often are different number of turns in different coil slots). And which way the coils are interconnected (for example, after going counter-clockwise around the innermost coil 150 times, it comes out towards you (when looking from the terminal end with the terminals on the left) on the left side, curves over to the right, away from the terminal connections on the case and enters the slot just to the right of the previous turns and returns in the slot to the left of the last turn).
Aside from that, you'll need to buy some 'magnet' wire of the same gauge. And while buying that, ask the same folks for some 'slot insulation paper'. That's the paper put into the slot first to protect the enamel on the magnet wire. Cut the paper 'long' so it extends out both ends of the slots to protect the wire from the edges. Some motors will use plastic/wood 'wedges' to hold the wire in the slot when your done. Some will put a small layer of paper over the coil before the wedges. Just take good notes when you take out the old winding.
If you take careful note of the details like which way each coil is turned, how many turns, how it goes from one coil to the next, how the coils on one side connect to the other side and to the terminals, you shouldn't have too much trouble. Screw something up, and you'll let out the 'magic smoke' when you turn it on.
OBTW, when rewinding, it may seem *impossible* that there was really the number of turns you counted in the slot. No matter what you try, you just can't seem to get that many turns to fit back into the same slot!!! Don't give up and skimp on the number of turns. One trick is to actually *pound* the copper wires into the slot when its about half full. Use a *wooden* slat or wedge over the wire. Place it in the slot over the wire, then use a blunt chisel or other narrow tool and a hammer. Gently tap on the wooden wedge with the tool/hammer to force the wire to compact into the slot, moving back and forth along the slot. This forces the wire tightly into the corners of the slot and tightly into place. Repeat the process when the slot seems almost full (and you still have what seems like too many turns more to go ;-). And one last time as you work the wedge into the slot.
Good Luck,
daestrom
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daestrom wrote (in part):

The devil is in the details ... that's why I opted to pay a pro. I had many opportunities to watch the winding of AC and DC machines and I came away appreciating the art involved in getting it right.
If you miss something about the way the motor was wound when you strip out the old wire, you're in a whole lot of trouble and it is unlikely that anybody can help you at that point.
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daestrom wrote:

Excellent stuff.
However, I would suggest that a very small number of turns missing on the start winding won't be the end of the World.
But, as you say, the odds are that the whole lot will have to come off and be redone.
LOL, these days (getting old...) I have taken to (digital) videoing what I am doing when I take stuff like this apart, with close ups of screws, bolts and other bits as I take them off. It saves having to remember which bits came out of which holes...
It also means I can send the video file to someone contemplating attempting the same repair and as an aide memoire for me for next time.
--
Sue










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Palindr☻me wrote:

Didn't you know that if you keep laughing you never get old?
The video sounds great. I had thought of using a sequence of still shots. I guess I would be a lot better off to borrow a video camera.
I think I'm going to try it.
I once made a plaster mold from a brass pitcher so my mother could duplicate it in ceramic. Two professional mold makers had told her that the pitcher was so intricate a mold would be impossible. She cast over a hundred of them from the mold.
I enjoy a challenge.
This is the first time I have ever gotten into a group on the internet. I like it.
Tom I'm in Illinois, USA
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Didn't you know that if you keep laughing you never get old?
The video sounds great. I had thought of using a sequence of still shots. I guess I would be a lot better off to borrow a video camera.
I think I'm going to try it.
I once made a plaster mold from a brass pitcher so my mother could duplicate it in ceramic. Two professional mold makers had told her that the pitcher was so intricate a mold would be impossible. She cast over a hundred of them from the mold.
I enjoy a challenge.
This is the first time I have ever gotten into a group on the internet. I like it.
Well, enjoy yourself. Beware of some folks that will pick a fight with anything, even a rock, just for the 'fun' of it.
Good luck with your motor.
daestrom
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daestrom wrote:

I had wondered about that. I'm familiar with the law of physics, or is it Murphy, that whatever comes out of a box will never go back in. So now all I have to do is put all this advice to work and see what happens.
I can't be worse off than I am now with a saw that doesn't work.
Thanks much
tom
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chefwho wrote:

This has previously been recommended:
Audel Small Electric Motors: Use, Selection, Repair, and Maintenance, 2nd Edition Rex Miller, Mark Richard Miller ISBN: 0-02-584975-1 Hardcover 436 pages April 1993
14. Stators-Stripping and Rewinding.
Stripping a Winding · Rewinding a Stator · Mold and Hand Winding · Automatic Coil Winding.
Can your public library get you a copy?
However, when I have repaired stator windings, I simply measured the wire size, counted the turns, and copied what was there. Quality yacht varnish did a reasonable job to keep everything snug. Only to be regarded as a medium term fix, though.
Rotor winding are a lot scarier to replace..
Why not open it up and have a look?
--
Sue











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Palindr☻me wrote:

Thanks, that's what I was thinking about doing. Just wasn't sure if it could be that simple. Roby commented about an experience of a bad relay having caused a burn out. Any thoughts on other things that might have caused it. I guess if I don't fix the cause it could just burn out again.
Will a motor repair place sell me the wire? Or, where do you get that kind of stuff?
How do you measure the wire size on that skinny wire? I'm more accustomed to measuring ingredients for cooking and baking
tom.
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chefwho wrote:

Overheating, damp, old age, etc.

I could only tell you about UK sources - which I don't think will help..

Like cooking and baking, you can often get things pretty close by eye. But a micrometer/vernier gauge is your "kitchen scales" - it can measure the wire diameter accurately.
I haven't clue where you are - but most towns, IME, have a little shop somewhere that repairs alternators, washing machine motors and the like.
Might be worth flicking through the Yellow Pages..
--
Sue


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Palindr?me wrote:
(snip)

You have Yellow Pages in the UK, eh?
Are the pages bound on the right-hand side?
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Roby wrote:

Hang on, I'll have a look....
Yep, you're right...
Anything left of centre has been banned by government edict..
--
Sue





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Taking a look is always a good idea. I had a motor with a "blown winding" and when I got a look at it the bad spot was right there. I just crimped a splice on it and put it back together. It worked for years
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chefwho wrote:

That happened to me about 15 years ago: DeWalt radial arm saw. As I recall, the shop wanted $200 to rewind (back then). What set off the failure was the little relay that disconnects the starting (before it burns out). Be sure to check it. I had the shop rewind my motor. They replaced the realy with a solid-state thingy.
Roby
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Roby wrote:

The shop told me about that relay. It looks like a burned set of points from a distributor. It was full of saw dust when I took it out. Looks like a cause. I think that's one of the parts that is still available. I'll also check with the shop to see if they have any of those solid state thingys.
Thanks for the tip
tom
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