On Thu, 02 Nov 2017 21:09:44 -0400, Ed Huntress
wrote:

On Thu, 2 Nov 2017 20:26:14 -0400, "Jim Wilkins"
wrote:

"Ed Huntress" wrote in message
. ..
On Thu, 2 Nov 2017 18:30:47 -0400, "Jim Wilkins"
wrote:


"Ed Huntress" wrote in message
m...
On Thu, 2 Nov 2017 16:18:31 -0400, "Jim Wilkins"
wrote:

"Ed Huntress" wrote in message
news:1unmvc95lkhs0ufmfla2ta6nanaamsk20r@4ax. com...
On Thu, 2 Nov 2017 13:38:23 -0400, Leon Fisk

wrote:

On Thu, 2 Nov 2017 13:24:25 -0400
Tom Gardner wrote:

I have a new 3.5hp (I think) "Works" largest 14" chainsaw that
I
want to
use the motor for a project. I need to know the RPM. I've had
no
luck
researching this and I no longer have an RPM meter. I imagine
all
chainsaws have similar rpm. I need to get the ratios on timing
belt
sprockets close to optimal. If this works, you will all be
dazzled
by
my brilliance!

Affix something to the chain that sticks out a little. Now make
another
attachment or hold something close by that will hit it. Like the
old
clothespin, playing card and bicycle spokes. Turn it on and
record
the
sound. Use something like Audacity to measure the frequency.
Viola!

A big, 16" bar, 15A corded electric Makita chainsaw has a
no-load
chain speed of 2900 ft/min -- 48 fps. I'd use my digital camera
in
timed multi-shot mode (10 frames/sec., I think) and take a
series
of
photos, and then measure the distance between a marker in two
sequential shots. You'd have to do it multiple times to be sure
you
get two visible, sequential photos with the marker.

Then work backward from the sprocket and chain pitches to get
the
motor rpm.

(Yes, there must be a simpler way.)

For reference, I saw specs on a Greenworks corded 14.5A saw that
said
6000 rpm. Another saw said 5500 rpm. A Remington Versa 12A 16"
says
3200 rpm.

If this is a cordless saw, all bets are off. As for 3.5
hp...that
sounds like Sears or Ridgid horsepower to me -- like 22A, if
they're
talking gross horsepower.

--
Ed Huntress

I've seen a rating in "electrical horsepower" calculated from how
much
juice it pulls, probably without considering efficiency or power
factor.

I think that some of them, including Ridgid, don't even go that
far.
They stall it and measure the current; multiply by the voltage;
divide
by 750; and claim that as "horsepower." My Ridgid shop vac draws,
I
think, 10A when it's running. But they claim it has "4.25 [peak]
horsepower."

HA-Ha-ha-ho!

--
Ed Huntress

We should call that "puke" horsepower since the motor is about to
toss
its magic smoke..

Yeah, that would be a better term for it. This is what Popular
Mechanics said about it in a shop-vac comparison. To me, this is
unbelievable:

"In addition to being designated by capacity, most wet/dry vacs
carry
a horsepower rating-our test units range up to 6.5 hp. But if you
think that means a vac motor is as powerful as a garden-tiller
engine,
think again. Like many other consumer-grade tools, the horsepower
rating is modified by the word "peak." This indicates the electrical
draw at the point where the motor is overloaded and stalls. The
upshot? Horsepower ratings aren't the most accurate way to compare
wet/dry vacs. Looking at amperage makes more sense."

--
Ed Huntress

Well, the motor is physically able to do it, just not for long.
Kettering made the automotive electric starter practical by designing
for brief peak power, 5 HP from a motor smaller than a 1/2 HP
continuous-duty motor.

-jsw

OK, but this isn't real horsepower they're talking about -- even for a
minute. They're defining "horsepower" as current times voltage (/747).

But if that's "horsepower, then you could have a really big power
resistor that developed 10 horsepower. g

That electrical value is "power," but it's just *potential*
horsepower. If you measured actual, kinetic horsepower, in terms of
torque times rpm, it would be a minute fraction of that. If the motor
is stalled, there's no real horsepower at all.

I wonder if Sears started that practice? That was the first place I
remember seeing it.
I think chainsaw horsepower is measured by how fast it cuts human
flesh.