Yesterday I was sorting my black locust wood into two piles – usable and firewood. And whilst cutting the wood, my little circular saw started to make a weird rattling noise. So I turned it off instantly. Then I disassembled it and I started to poke around in its guts to see if I can find what is the issue. I have thought that I found it – two ball bearings were a bit worn and had a rough feel to them so I have replaced them. Then I have assembled everything again. The weird rattling noise was gone and it was running smoothly.
Hooray! I plugged it in and started it and I rejoiced for a few seconds until a billowing cloud of smoke emerged. The stators isolation has suddenly started to burn, god knows why.
I have already ordered a new, better and bigger circular saw, a proper, stable, table saw (this one was handled saw fixed to a table). I am glad that it died now when I still have some money to spare rather than later when I run out and have to chew tree bark, but I’d be happier if it hadn’t died at all.
Well, it had a good run at least. I have bought it nearly twenty years ago and the first thing I used it to make was a table for my PC. A few years later I have used it to build another, bigger and better PC table, accompanied by a bookcase, a wardrobe, and a small tea table. Then came my own set of back horn speakers and several smaller projects. I have used it to cut material for my belt grinder and to build a lot of my current shop furniture.
I still have all those things and they serve me well, so the saw did pay its purchasing price several times over. When I have disassembled it, there was noticeable wear in the gears, so even though I did not feel like I have been using it that much, I was using it enough and it did not die prematurely.
I hope the replacement arrives soon. I have a lot of work t do.
For many years I used an Electrolux vacuum cleaner that my parents got when they were married in 1950. Before the days of planned obsolescence, they knew how to build things that would last forever. A disaster for the company’s profits, of course.
Alas, I finally had to get rid of it after 55 years of running perfectly. There was nothing wrong with the machine itself, but the cord had to be a certain shape to attach to the machine, and it broke off right at the head where it was unspliceable. Needless to say, the Electrolux store just laughed when I asked if they still made cords that would fit.
I don’t know if this is actually true or not, but I read somewhere (I think a bicycle repair website?) that if any ball bearings are bad, the whole set should be replaced, and replaced with ones from the same lot(?), as there may be small imperfections or size differences that would cause uneven wear and early replacement.
Maybe that’s just bicycles, or maybe it’s not true at all, I dunno.
About twenty years ago, I bought a set of Bosch (24 volt?) cordless tools (drill, circular saw, and reciprocating saw) that served me pretty well. I built my bed, a couple shelves, a weird ‘bench’ thingy, a couple aquarium stands, and a bunch of other stuff I don’t even remember. Gradually the various batteries started to perform worse and eventually fail. A few years back, the last battery failed, and I looked into getting new batteries, but the only things I could find were really sketchy and off of ebay. Also looked into cordless battery “adaptors” to try and use other brands/models batteries, but again, super sketchy and only off of ebay… then I looked into trying to rebuild them, none of the places near me who offered such services would be willing to do so, and rebuild “kits” were at least a couple hundred, and I didn’t trust my soldering skills enough to think it was worth the risk.
Ended up buying some Milwaukee M18 cordless tools, got some decent deals with Black Friday or something, and i’ve been quite happy with them. There’s been significant advances in technology and such, so my tools are smaller, lighter, more compact, more powerful, have nicer features, and the batteries are also lighter, more compact, and more powerful (my old Bosch Ni-Metal-Hydride ~3AH battery was about the same size, maybe bigger then my current Milwaukee 9AH battery). And most of the tools have built-in LED lights, which is pretty minor, but a nice touch. I’ve been really happy with them so far, and am glad I upgraded to more recent tools.
Electric motor insulation degrades with time, especially if the motor is running hot. The higher the (electromagnetic*) torque and thus the current through the motor is, the more heat is generated. The degraded insulation may leak more easily, partially shorting the windings and thus the current may get even higher even when the torque is lower.
Voltage also degrades the insulation. If the motor is a permanent magnet motor (brushless motor**), switching the motor off*** while it’s rotating freely at a high speed may cause a high voltage and possibly arcing in the stator winding unless the current is directed to a braking resistor. I don’t know how power tools and their motor circuits are designed in this matter.
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* = Electromagnetic torque is the torque that is generated by the magnetic fields, felt by the rotor, the mechanic torque of the motor is the electromagnetic torque minus the internal friction and drag torque in the motor.
** = Or any other motor in which the magnetization remains when the power is switched off.
*** = When you cut the external voltage, the motor becomes a generator unless the magnetization is also lost.
One further thing: If the rotor was able to impact the stator because of the loose bearings, that may have damaged the stator insulation, which may have caused a leak.
@Ice Swimmer, this is a brushed motor, so it cannot generate electricity when the power is cut off.
I suspect some sawdust got there, maybe even caught fire from friction or the sparks from the brush, and damaged the shellack insulating the wires. And once that was damaged, there was a runaway reaction that has made the short-circuiting escalate really fast.
The stator could be bought, but it costs about 30% of a new saw, so I have disassembled the saw today, thrown away everything that is of no use, and stored all the screws, ball bearings, and aluminium for future projects. And I will buy the handheld saw new when (if) I need it.