On 12/6/2011 1:10 PM, Randall wrote:
>> I can't speak to the motors burning out,
> I have several HF electric tools that have performed well for quite a few
> years. I really didn't expect the angle grinder to last, as it sounds
> hideous, kind of like a buzz saw cutting through a bee hive, but it is still
> going strong over 20 years later.
>
> But the first die grinder I got from HF died within seconds. A quick
> inspection showed that one of the field wires had gotten tangled in the
> rotor. This was not a matter of incorrect break-in or operator abuse;
> obviously a manufacturing defect, and clearly the motor had never been
> tested.
>
> So IMO it's just the luck of the draw. The designs are OK, materials
> marginal; but quality control is totally non-existent. The replacement die
> grinder worked just fine.
>
> Oh, and IMO the break-in instructions that were quoted are of questionable
> benefit at best. They might possibly contribute to longer brush and/or
> commutator life; but brushes are a consumable anyway and I don't recall ever
> having an electric motor disabled because the commutator was worn beyond
> use. Even worn out brushes are pretty rare in my experience (mostly in 50+
> year old equipment, like the original generator on my 56 TR3).
This appears to be a knock off of the "As Seen On TV" tool. Don't know
the specs of the original or actually how well it works, but the link
says this model has a 7.5 amp motor which seems light for a saw. It's
has a 5" double blade so I'd expect it to need the same power as a 7.5"
single blade circular saw. My circular saw is 10 amp and still whimpy.
My old corded drill is 9 amp. The 7.5 amp is more than my 4.5" angle
grinder, 5 amps. Since it's a knock off I would not be surprised if the
actually power delivered by the double blade saw (efficiency of the
motor, added gearing to run two blades, general quality, etc) was
comparable to my angle grinder, not enough IMHO for a saw.
Can't speak for the validity of the break in advise. As Randal pointed
out I don't think the brushes are an issue since they are spring loaded
and bear no load. Randal obviously proved his motor was never run so
the bearings were never broken in. Breaking in for the bearing makes
sense. Initially the machined bearing surfaces are a little rough.
First time the motor is run those surfaces will heat up. If you put it
immediately under load I could see that surfaces might anneal and dig in
instead of wearing evenly.
Then again everyone pulls the trigger a few times on a new toy, I mean
tool, anyway. At least I don't think breaking in the motor would hurt.
Food for thought.
Peter T.
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