On Thu, 02 Nov 2017 14:29:51 -0400, Ed Huntress
wrote:

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.
Remove the chain and take the thing to an RC hobby shop. They will for
sure have optical tachs for sale. They will probably check the RPM for
free if you ask nicely. Make a constrasting mark on the sprocket
before you bring it in. Maybe color half the sproket with a black
Sharpie.
Eric