A neighbor asked me to have a look at this polisher. It was pretty clear that the switch had disintegrated and needed replacing, but just look at the construction and fixing arrangements for the motor:



The bearings sit in plastic moldings in the two halves of the casing. The shell of the field stator assembly relies similarly on two little plastic lugs on the case moldings to keep it from rotating, as you can see from the little notch on the end.

The brush and rectifier assembly is on a plastic carrier which just drops on to two more moldings on the bottom half of the case and relies on a couple more projections on the top half to keep it in place:



Now is it just me being picky, or does this seem like a really cheap and nasty way of constructing a motor for a power tool? The whole thing seems to rely entirely on the two halves of the case being perfectly aligned just to keep the armature correctly centered within the field.

Oh, and when I pulled the armature out of the stator in order to get everything lined up and re-assembled, look what happened. One of the field magnets just came straight out with it! I guess they skimped on the glue.




[This message has been edited by pauluk (edited 04-04-2005).]

Hi Paul,
Yes these tools definitely aren't made with any sort of longevity figured into the design or manufacturing processes.
How much would a tool like this cost to purchase?.
I'm guessing that it's one of the very cheap brands, like the one's here that have popped up at our supermarkets.
I've never thought of buying an Electric Drill with my groceries.
But generally they are priced under NZ$20 and as the old saying goes "You gets whats you pays for".
Paul I take it this is a Double-Insulated Appliance, but in the bottom pic there is a screw holding a wire and terminal to the outer part of the motor "body".
This obviously isn't for any kind of earthing is it?.
Going by the brushes and the commutator, the brushes aren't applying equal and even pressure on the commutator either.
I wouldn't personally use a tool of this particular quality for very long in one spell, it may melt in your hands, given the large amount of plastic in it's construction.

These days, I'm afraid it comes down to one of 2 things
<OL TYPE=1>

[*]Is it going to last 12 months?

[*]If no to first question, is the number of returns and replacements multiplied by the cost going to be smaller than the profit margin?
</OL>
If either of these is yes... YAY, sell garbage, rake in the money.
The PC industry does the same, everything's about price, whereas years ago people would think "if I buy this which is 3x as expensive, it will be better" and they'd be right. Now it's "3x the price? RIP OFF" and they walk away and buy the cheap stuff

I'm afraid you're right Chipmunk. This unit is just out of warranty apparently.

Yes, it's double-insulated with a 2-wire cord. The connection is part of the interference suppression. It just goes to a twin capacitor (you can see it lower left in the first/second pics), one cap to each side of the supply.

It's a Draper -- Sold widely here in the lower end of the power tool market in DIY chains, supermarkets, car accessory shops, etc.
http://www.tooled-up.com/Product.asp?PID=91557

The build quality of some PCs is absolutely terrible. They're just whacked together with the cheapest possible parts. Particularly, the electrical components, e.g. power supplies and fans!

Paul
I have just taken a 10 year-old Makita 750W mains-operated drill apart to assess a problem with the brush gear/armature, prior to getting it repaired. Inside, it's built like a Swiss watch, beautiful machining and gears etc., but all the stator/armature assemblies are located by the plastic case mouldings- it's the double-insulated construction method. You can mould plastics to 0.001" with care. Cost new now about = $180US here. I can get a similar-size Chinese drill in the supermarket for =$12US, but this tool will disintegrate if stressed like a Makita or a Porter-Cable. These cheap tools are strictly for the DIY 'play' market, ( I remember my sons having those 'Junior Carpenters' Tool Kits' 25 years ago- complete crap, but still capable of sawing the legs off their beds! ), - not intended for a proper skilled craftsman to earn a living with. The market for power tools has fragmented into many sectors to cater for all users, and low Chinese labour rates ($25US a WEEK!) have enabled this to happen. To be fair to Draper, they have some excellent high end market tools as well- only sold through Pro tool shops- I have a Pro Draper 16 gauge brad-pinner, 12v NiCd with on board air-compressor & it will fire 2" brads and bury them in oak planking, hour after hour. It has operated faultlessly for 2 years. Even Makita have a DIY-type range now- (orange casings). Still built like a Swiss watch - but by far-east labour. Trumpy is dead on with his comment- you aren't going to get Robert Bosch quality for $12 US - all tools are not built equal. Mind you, the polisher does rather look like a POS inside, doesn't it!
Alan

Draper tools on http://www.drapertools.com
Should have typed 18 gauge.
Current mrp in the UK is = US$680
Ouch!

This is the motor from my Robert Bosch cordless drill/screwdriver
http://www.gideon.e7even.com/bosch1.jpg

I'm still a fan of their stuff.

I bought one of those $20 drills that Trumpy posted about, for use about the home workshop. The reason? It came with a 13mm chuck which none of my other drills had, and a new 13mm chuck would cost about as much.
My opinion of this drill? Well I wouldn't give it to a tradesman to use at work (it would have a depressingly short lifetime, I fear), but is seems quite well constructed and should last OK at home as long as it isn't abused. The speed control is fine enough to let me drive 2 1/2 " woodscrews without destroying screws and bits. It came with a spare set of brushes too, which I thought a nice touch.
All in all not a bad effort for $20.
My switchboard-building workmates here favour Makita or De Walt power tools, and seem to get a good run out of them.

"This unit is just out of warranty apparently."

They pay engineers good money for that kind of timing! After-all its the LAW, or at least in the US it is. Act of congress in the 70's - Planned Obsolecance - Consumables get a varied life expectancey. Cars 3-5 years, down from 5-7 years before major repairs. And the only things really allowed to last are Military, and Farm Equipment, are allowed to last 50 or more years through limited repairability.

The tool you have there is considered consumable.

Paulus,
Welcome to ECN, mate!.
I see that you are in Christchurch, NZ.
Hi from down the road.
Fact of the matter here, is they put vents on power tools here to let the smoke out, not the air in.
Mark (e57), is darn right in his post, pretty much the world over, there is a market for these throw-away tools.
I, as an Electrician, used to attempt to repair tools like this (only on a very slow day), but 90% of the time, you'd open the case up (once you'd got the Security bits) and find components you couldn't even work with.
Solution, close it back up and send it back to the owner.
Problem is these days, there is a ready market for "disposable" power tools, mainly the weekend DIYer.
Also, there are people that give a note on the tool "Do not repair if price over $XX, please advise"
I was taught as an Apprentice Electrician, to Buy Once, Buy Well
Problem is the DIY market is bigger than us Tradesmen buying power tools, it's only a matter of time before the same manufacturing processes are used, for our tools.

Yep, these sort of tools are certainly intended to be consumable. Even though the initial problem was just the switch (standard size, cost 79 pence for a replacement), most people would have just figured they'd got their year's use out of it, toss it in the trash and go buy another one. These things only get repaired (if possible) these days when it's for family and friends.

By the way, I forgot to mentioned the plastic clips holding the brush springs which you can see in the second pic. It seems they have some sort of ingenious automatic release system in them so that you only have to look at them cock-eyed and they fall off sending the spring across the room.

You can never get the dozens of stupid little parts to stay in one place while you fit the two halves back together. Then the wiring, why must it ALWAYS get trapped between the 2 shells? And the blasted screws! One of then is certain to drop 3 feet to the floor, with not the slightest provocation and totally vanish. Then, contrary to all the Laws of Motion of the Universe, it transports itself 45 feet to the other end of the shop, behind a cupboard. But somewhere in the world there's a production line where a smiling deft-fingered operative is assembling one of these things every 10 seconds, with her left hand, while holding jolly conversations with her workmates!
Why me, Lord, why ME?

Good call fellas,
Paul,
Even them brush-holders look cheap, most power tools I've opened up have the wires feeding the brushes entering from the ends of the holder.
Alan,
You are darned right about the small bits from tools.
I find that an old egg carton works wonders so that you can group the thousands of screws that come out of these little buggers.
Also you can use the carton for something to bite when the Damn thing won't won't fit back together!.
All that and Mr Owner want's the thing fixed economically. GRRR

My local Woolworths store is selling drills and angle grinders for $14 bucks NZ. Thats $7 U.S. and 5 pounds U.K. You can't possibly manufacture decent power tools for that money ! !

I bought a Rigid 14.4 volt cordless drill and have been nothing but happy with it. Payed $150US for it, one of the major reasons I bought it was because of the 3 year "no questions asked" warrenty. I have put it through the mill, dropped it off a ladder 6' up onto a cement floor and it still works just as well as the day I bought it. Whats sad is that my friend bought a "China" 18 volt cordless from a import tools store *cough*Harbor*cough*Frieght*cough* for 40 bucks, right now it sounds like the gearbox is on its last leg, battery wont hold a charge, and doesnt even compare to my Rigid in terms of tourqe or power. Whats even sadder? He only bought it 2 months ago for basic home repair stuff.

[This message has been edited by bensonelectric (edited 04-08-2005).]

paul
Just realised: this motor runs on rectified dc with those diodes? Is this connected to that 'universal motor' thread posted some time back?
Alan

Not sure which thread you're refering to, but I didn't have another one in mind specifically when posting this.

And yes, the permanent magnet motor with rectifier struck me as an unusual arrangement too.....


[This message has been edited by pauluk (edited 04-09-2005).]

Paul
Thread was posted by splitzapper in the Electrical T&A Forum 01 21 2005.
So, "I put my thinking-head on.", as Worzel Gummidge used to say, and surmise that the motor would be series wound dc: speed is effectively controlled by the load. For a polisher, you'd get very high speed when lightly running a mop over the work, and vice-versa. Only vaguely connected with the above thread, and spitzapper never did get an answer to a rather vague question.
alan

Still had the 'thinking-head' on; I'll bet splitzapper was considering using a universal motor (from a drill?) and a dc source ( batteries?) for a project. Let me guess- an electric bicycle? a DIY powered lawnmower?
NOT a good idea, safety-wise.

Alan