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 Post subject: MacAllister mitre saw
PostPosted: Thu Mar 03, 2011 3:31 pm 
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Hi all new here so be as brash as you like :-) .
I unfortunatly bought a MacAllister 1800W compound mitre saw in 2008,and it is now BROKE :cb nothing
unusual there then.
I the gullable sort that I am want to repair it, it has only had very light use 18mm x 32mm nice clean picture frame in fact its made approximatly 350 cuts,now even i know it should do alot better than this.The brushes are in very good order but on pressing the trigger it gives of a very bright crackely spark from the brush area,on examination it looks like the motor or comutator is burning out,not sure of the exact terminology but i think its close.
I am currently sending emails to B&Q to see if they can tell me if its possible to get hold of parts for it,and GMC the distributers whom say "they get shipped in from china to us and spares are'nt available to us" :scratch: .
I used to fit pvc and occasional hardwood conservatories so thought this saw would be ok for cutting lightweight materials such as pvc,anyway I did'nt get a chance to use it on conservatories as the work dried up so it sat in its box for six months before I used it.
I guess this is a warning about these chinese machines that although they may be ok and last some people a long time, when they do break then its just another chuck away item as you cant get parts for them(except brushes).If I can get the motor I will be a happy bunny :huray:.If I cant I have some good spares for someone with the same machine.I'll keep you updated as to the outcome thanks for reading my tails of woe.


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PostPosted: Thu Mar 03, 2011 3:50 pm 
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google imported tool spares
these people are realy good
http://www.80578057.co.uk/

023 8057 8057

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PostPosted: Thu Mar 03, 2011 4:24 pm 
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Thanks big-all but used them before for parts and were great but this time around they just say its not cost effective to import the motor, so looks like B&Q wont be getting anymore of my business in the powertool department.
As a warning to other buyers of cheap B&Q aldi lidl machinemart and others powertools do your research and see if you can get hold of parts for the tools you are buying, not just brushes but major parts as well.Check out the parts you can see on a powertool like the plastic parts, back plate,levers etc, and think about some of the parts you cant see like the motor, brush assembly, trgger internals,bushes for sliders.
If you cant get some of these parts It is probably worth looking for alternative tools that you can get major parts for.


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PostPosted: Thu Mar 03, 2011 5:33 pm 
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I'm sorry but have i missed something here? Does the saw actualy work?, because all im reading is the saw hasn't been used much. So its been left standing for a while sometimes. That just makes the commutator copper oxidise on its outside edge which the brushes run on and that does make sparks when electricity is put through the brushes because it has moisture in the oxidised copper and what has been rubbed off onto the brushes. So realy theres nothing wrong with the motor or the commutator its just you worrying about nothing.


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PostPosted: Thu Mar 03, 2011 7:27 pm 
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No its not standing around when I purchased it it stayed in the box for six months,the saw was been used when it suddenly started sparking and we are not just talking little electric flashes we are talking full blown ring of sparks that crackle when the trigger is pulled.


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PostPosted: Thu Mar 03, 2011 8:45 pm 
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Well that sounds like the brushes are decaying and have burnt out then, not the commutator or motor. If those last two were broken then the saw would possibly not turn or if they did it would be realy noisey.
Can you get to the motor / commutator and the brushes and post afew pics of them all.


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PostPosted: Thu Mar 03, 2011 9:04 pm 
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The brushes are in good condition as stated in my post, and yes it is noisey the sound is just like brushes on the way out but quite fierce sparking almost a white circle as it spins and a lack of power,I guess the comutator may have a bad gap in its segments as between I can see some burning, I will get photos of the brushes and comutator tommorow, on measuring the brushes it looks like they have only worn about 3mm off.


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PostPosted: Fri Mar 04, 2011 1:15 pm 
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Sorry about the quality a bit dark in my studio.But does show nicely the brushes still 17mm long,the burning and scores are from the comutator.
I remember when armatures could be rewound,I guess its to expensive to do nowadays thats if its possible to find someone to do it.


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PostPosted: Fri Mar 04, 2011 1:17 pm 
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The comutator not looking to good.


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PostPosted: Fri Mar 04, 2011 10:45 pm 
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From looking at the brush it looks like it isn't being held in it's holder properly that causes electric current to burn the carbon that makes the brush work thats why your getting the ring of sparks, check with the brushes in place if they move about. If you look at the pic you've posted it looks like its being worn down at an angle, that shouldn't be happening. Then i looked at the commutator pic and it does look as though the brush holders aren't holding them in place properly as the saw motor spins i say that because the edge of the brush is rough, it should be smooth not rough at all. Another sign that the brushes are burnt out is the carbon left on the commutator, thats not natural wear thats burning of the brushes which means they are decayed from over heating that also happens when more electric current than needed is passed through the brush, thats happened because they aren't touching the commutator at the correct angle.
You may be able to fix the commutator by using a pencil rubber to remove the burnt on carbon residue, when its cleaned off then you can run your finger around and over the copper strips to see if they have any sharp edges and are raised or loose. Unfortunatley if any are loose then its scrap. And if any are raised you may be able to hold a fine metal file against the edge and turn the commutator against it to take the top outside edge off to give a flatter surface to run on.
Can you give a couple more pics of both the brushes and what they are held in place with because you might be able to fix this.


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PostPosted: Sat Mar 05, 2011 1:14 am 
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brushes and commutators can often glaze over during cold damp storage this causes bad contact and arcing
this can damage the commutator brushes springs and connected joints and wiring

do not use the machine unplug from the mains gain access to the brushes and commutator
rub the bearing face off the brushes on a fine needle file or fine emery on the carbon brushes only to give a clean new rubbing face
clean the commutator with braso /silver polish nothing more abrasive and wipe fully clean after use

you need to be sure the brushes are long enough and the springs haven't suffered with overheating
typical overheating damage is lack off spring pressure or travel

brushes may look long enough but check if they have physical connections like braided copper that there is enough movement to allow proper contact

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