Thread: Waldown 6” bench grinder rewind schematic help

I have another thread in the Metalwork projects section around restoring a Waldown 6" bench grinder: https://metalworkforums.com/f303/t20...storation-lots

I have decided to start a new thread here since this is more suited to members with an interest in electricals and some knowledge on the subject.

Does anyone have a schematic of a single phase 2 pole centrifugal start motor configuration? I have tried searching the internet but everything seems to be focused around 3 phase and DC motors these days and a few common schematics around single phase 4 pole motors.

Here is a photo of the centrifugal switch side of the motor and the start windings are on their way out:

Stator image.jpg

Another quick visual inspection reveals that the stator is tacked in place and cannot be separated from the motor housing. I could grind off the welds and press the stator out but that makes it no easier to rewind the motor. There is also welding spatter between the stator and the motor housing which indicates it was probably just welded in place prior to the factory winding was put in place else there are chances to damage the enameled copper windings.

Basically the motor data that I have collected so far and based on my visually studying the motor, the winding schematic can be summarized in the following diagram that I quickly put together in powerpoint:

Motor winding template.jpg
There is a key way and markings on the AC side of the motor that indicates where slot 1 is referenced from.

I am yet to determine the number of turns for the start and run windings and the wire gauge after I pull out the old windings. Visual inspection also seems to suggest that the start windings have different turns when comparing the inner slots to the outer slots.

This is where I request members to provide me feedback? Did I miss something in the connections or did I trace/map a wrong connection?

I wish to finalize this information before I start to remove the old damaged windings and clean the stator in preparation for a rewind before I hand it over to a sparky mate that I have known my entire life for the actual rewind

Any feedback? Or documentation will be highly appreciated.

Does your sparky mate know you are doing the strip down? If he does, he's a new kind of motor winder. I personally would not allow anyone to strip down a motor that I was going to rewind & certainly not rely on another to take the data. I've done some decades ago, used to enjoy it, but no, not interested. By the way, it's not usual to remove the stator.

So if someone brings a motor re-winder a new stator and gives them the specs of the motor (desired RPM, voltage, amp draw, hp or kw, application needs….) they will not be able to guesstimate a winding for it?

I think there are formulas out there for stator volume, wire gauges, number of turns, amp draw etc that can be used to parametrically design a motor for a specific task?

These are some fairly common motors we are talking about here.

Originally Posted by kafie1980

So if someone brings a motor re-winder a new stator and gives them the specs of the motor (desired RPM, voltage, amp draw, hp or kw, application needs….) they will not be able to guesstimate a winding for it?

A professional motor winder/electrician doesn't 'guesstimate' anything. In my opinion your 'help' is only overcomplicating a simple job. If you really want to help just give the man the motor as it is. If, in my day, I was given a gutted carcase to rewind I'd have charged at least double.

Here's a link to my experiences at a first attempt at motor winding

https://metalworkforums.com/f65/t200...ghlight=arboga

In my case I had the original 3ph motor rewound to operate on single phase and then some years down the track I rewound it back to 3 ph so I could operate it with a VFD, the original 3ph winding layout was unknown to me so I had to do a lot of research to determine the coil layout, it was complicated by the fact that the original 3ph winding was 2 speed, I did get a lot of help from the eng-tips.com forum, while none of the forum members gave me the winding layout solution they did guide me and steered me in the right direction until I had it right.
If you are going to hand over the rewind to a mate perhaps you might want to be there when the old windings are stripped out, and documented - take lots of photos, I found a paint stripping heat gun was useful to soften the varnish, make sure you document the size of the coils I believe the start and run coils are different sizes - good luck.

I did read your thread on the Arboga mill 3 phase motor rewind a couple of weeks ago with great interest

I found that business at Beverly SA that you mentioned in the thread and you did mention 5kg spools of winding. I wondered if that is the minimum quantity they sell? I might drive there at some stage myself and ask them.

I do have a 1kg spool of 0.5mm enameled wire that I bought years ago when I lived in Malaysia to rewind some 3 phase brushless DC motors used on quadcopters and have about 400+gms left. We would just walk over to the supplier with an empty spool and they would sell us per kg which made it fairly cost effective

Capture.jpg

Yes the start and run coils are different gauges and I have just updated the winding schematic. After carefully scrapping some of the enamel I measured both use a micrometer and a digital caliper and they are different. The run windings are 0.7mm which is double of the diameter of the start windings that's are 0.35mm. There are also fewer turns in the start windings compared to the run windings which kinda makes sense.

I will take notes on the rough size of the coils as well. And importantly the number of turns if I get that far.

I do have a 2000w paint striping gun in my arsenal to deal with the varnish

Advance Thermal Supplies Pope St Beverly, I still buy my transformer wire from them - they like a min order of 2Kg - at $27@Kg plus GST it isn't a huge cost so you may as well get enough for the wind plus a bit to spare to cater for stuff ups, they also have insulation in sheets - you'll need some to insulate the motor slots, I used what I had on hand for transformer winding - 0.15mm thick, you also need some sort of insulation to go over the top of the coil once it is place in the slot, both to insulate and also hold the coil in place, you want to be sure the coils always have insulation between them and the motor frame - I've seen thin strips of timber used and I did try to make some but gave up and used the same insulation folded double thickness and then formed into a long strip with a 'U' cross section pushed into the slot to cover the top of the coil, watch as many youtube videos as you need to, to see how this is done. I used ordinary polyurethane floor varnish to anchor the coils once they were all in place - with the motor sitting vertical I just kept flooding it in with a brush over 3 or 4 days, to try to get it all through the coils to keep them anchored, the varnish has stood up to prolonged use for over 5 yrs now.
If you're not sure of the minimum amount of wire you'll need it's easy enough to work out from the number of coils, turns per coil and average length of one coil - wire tables will then give the weight per meter - once again good luck.

Thanks for the useful information.

You are helping me build courage to do it myself

Price for the enameled wire is not much. The MOQ 2kg they sell, do we need to bring an empty spool? Or does it come pre-packaged?

I used to have sheets of mylar for insulation but can’t find them, so go to know I can buy them at the same place.

Yes, wood, they have used wood, flat pieces to separate the start winding from the run winding, and round pieces to hold the windings in the slots.



The flat sticks look similar to and closer in size to the cheap coffee stirrers that I use for mixing paint and stirring chemicals:



The round wooden pieces can be made from wooden dowels stock sold by the meter lengths at the big green stores.

I will need varnish, hoping the shop has some?

I have a really old can of German urethane spray but it’s lost all its gas. I used this back when I was into electronic circuits.



MgChemicals sells a brush on red varnish that I can order online. It’s an air dry formula but a bit pricey.


I bought a mould for making the coils from AliExpress for $17 shipped. I could have printed them but the time and money to design and print and make the mounting brackets and fasteners is not worth it to me.


I can make the rest of the manual winding setup out of some wood scrap I have laying around. Just a simple spindle with a crank handle mounted in a vice (I am not even going to bother with bearings and gearing). Bcause that was like $50+ and infact about $100 if I wanted the model with the counter.

Advance Thermal will supply the spool, they don't have despooling equipement and give that over to a third party so if you supply a spool you'll need to drop it off and then return to pick it up once your wire has been run onto your spool.
Looks like you are well on the way - one last thing don't trust yourself counting the turns, you only need to be distracted for a few seconds to lose count, fit a turns counter of some sort, over the years I've seen turns counters made from cheap handheld calculators and also tally counters, youtube is good here to see how others have done it.

Now you have sparked another side project in my mind regarding the counter:

I am imagining setting up a hall effect sensor coupled with an Arduino board and a simple display to work as a counter.

Not something I wanted to do and I will need to look through my pile of electronics junk to see if I can cobble something up.

Might be easier to just do something like this for a counter.

EEVblog #962 - Hacking A Calculator Into A Counter - YouTube

Originally Posted by swarfless

Originally Posted by kafie1980

So if someone brings a motor re-winder a new stator and gives them the specs of the motor (desired RPM, voltage, amp draw, hp or kw, application needs….) they will not be able to guesstimate a winding for it?

A professional motor winder/electrician doesn't 'guesstimate' anything. In my opinion your 'help' is only overcomplicating a simple job. If you really want to help just give the man the motor as it is. If, in my day, I was given a gutted carcase to rewind I'd have charged at least double.

Agree 110% with your thoughts regarding help actually being a hinderance in many cases and I can think of many instances withing my own trade where this has played out.
The question posed by kafie1980 does however spark my interest, purely for the theoretical information side of it. I guess there must be tables or equations used by motor designers that they use as a starting point when designing or constructing a motor to perform a specific task. I realise that motor winders meticulously count and copy the existing windings when rewinding motors, but is there scope for a motor winder to customise/improve/modify a given motor and if so, do they base any changes around knowledge gained through experience, or are there mathematical resources that they utilise?

Nice option. But I need to find the calculator and I don’t have a hall sensor or a proximity sensor in my junk box.

I have an Arduino nano board but have no display.

I did find some bits and pieces from an old broken 3d printer that has given me a simple idea to make a stepper motor based direct drive winding jig supported by bearing blocks I could belt drive it too and have pulleys but have a fairly long closed loop GT2 belt which I don’t like.

If I go with the 3d printer components the I can just use simple Marlin g-codes to give me the number of revolutions I need via the extruder driver. Not as fast as hand winding but even if it take double the time I will not have to focus on counting turns

Too many ideas, and it all started with a counter

Originally Posted by Karl Robbers

Agree 110% with your thoughts regarding help actually being a hinderance in many cases and I can think of many instances withing my own trade where this has played out.
The question posed by kafie1980 does however spark my interest, purely for the theoretical information side of it. I guess there must be tables or equations used by motor designers that they use as a starting point when designing or constructing a motor to perform a specific task. I realise that motor winders meticulously count and copy the existing windings when rewinding motors, but is there scope for a motor winder to customise/improve/modify a given motor and if so, do they base any changes around knowledge gained through experience, or are there mathematical resources that they utilise?

You are spot-on, Karl, regarding copying existing windings, & there's generally not much scope for improvement except in insulating materials, but changing a motor winding for a different voltage is pretty common & just as straight-forward, & generally covered during apprenticeship, was in mine. A good practical reference is 'Rosenberg' if you Google that. I think it's still in print, at least I did see it come up about a year ago when searching for something else .. maybe in a 2nd-hand bookshop? Rosenberg saves you having to do much more than looking up the appropriate table to come up with a new winding .. I mean, it's only simple arithmetic but why bother?

Thanks for that Swarfless. I worked next door to a motor rewinding business for 10 or so years and saw quite a few little snippets of what they did and how they went about it. There used to be at least three motor rewinders in town, but now we are down to one and they aren't exactly run off their feet. I guess the cost of rewinding the average motor being so labour intensive, has overtaken the cost of a new motor in many cases.