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#120280 04/04/05 06:59 AM
Joined: Aug 2001
Posts: 7,520
pauluk Offline OP
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:

[Linked Image]

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:

[Linked Image]

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. [Linked Image]

[Linked Image]

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

#120281 04/04/05 08:44 AM
Joined: Jul 2002
Posts: 8,432
Likes: 3
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.

#120282 04/04/05 05:56 PM
Joined: Jul 2004
Posts: 145
These days, I'm afraid it comes down to one of 2 things

[*]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?
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 [Linked Image]

#120283 04/05/05 06:31 AM
Joined: Aug 2001
Posts: 7,520
pauluk Offline OP
I'm afraid you're right Chipmunk. This unit is just out of warranty apparently.

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".
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.

I'm guessing that it's one of the very cheap brands,
It's a Draper -- Sold widely here in the lower end of the power tool market in DIY chains, supermarkets, car accessory shops, etc.

#120284 04/05/05 02:18 PM
Joined: Dec 2002
Posts: 1,253
djk Offline
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!

#120285 04/05/05 02:29 PM
Joined: Mar 2005
Posts: 1,803
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!

Wood work but can't!
#120286 04/05/05 03:02 PM
Joined: Mar 2005
Posts: 1,803
Draper tools on
Should have typed 18 gauge.
Current mrp in the UK is = US$680

Wood work but can't!
#120287 04/05/05 05:24 PM
Joined: Dec 2004
Posts: 161
This is the motor from my Robert Bosch cordless drill/screwdriver [Linked Image]

I'm still a fan of their stuff.

#120288 04/05/05 08:18 PM
Joined: Jun 2004
Posts: 56
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.

Mark aka Paulus
#120289 04/05/05 10:41 PM
Joined: May 2003
Posts: 2,876
e57 Offline
"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.

Mark Heller
"Well - I oughta....." -Jackie Gleason
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