On Sun, 11 Mar 2012 05:00:55 +0000 (UTC), David Lesher
wrote:

So the place wih big toys has 120V 12-14" cutoff saw. Rather like this one:
http://www.drillspot.com/products/62747/Milwaukee_6180-20_Abrasive_Cut_Off_Saw?s=1a

It's a PITA, it regularly trips the 20A breaker under heavy
loads. {Why would anyone make a power-pig like that NOT
120/240???}

Sorry to dredge up the dead, but it has to be said - and wasn't...

IF that abrasive chop saw has a motor that is rated at 15A full load
and is installed on a dedicated 20A circuit, and is tripping out a 20A
breaker on a regular basis, that saw is trying to tell you something -
BACK OFF THE FEED PRESSURE when the spindle RPM drops off - you
are probably close to stalling the motor to get the breaker to trip.

You're going to release the "Magic Smoke" from the motor, then you
have to throw it out and get another chop saw.

If this is being run by an employee who doesn't care if he burns up
company property... Build an ammeter into a box mounted above the
machine, and tell them to stop pressing down so hard when the needle
hits the red line drawn at 15A. If it gets extreme, you might have to
lock the breaker panels and make tripping the breaker an infraction
for abuse of company equipment...

And if it isn't on a dedicated circuit, you need to get it on one -
chopping the power off at full load and instantly stalling the spindle
isn't good for the motor. It cuts the cooling air when it doesn't get
a chance to coast down unloaded, and you'll burn up the motor.

Got to wondering... how popular/available are air powered bench
cutoff saws? That shop has a good air supply given our duty
cycle.

Air power is very inefficient for a large stationary tool like that -
conversion losses would override the burst power advantages.

IMHO the only way it would make sense is in an explosive atmosphere
like a refinery where you don't want to make any more sparks than
necessary. Or on handheld tools where a 2HP electric drill gets
rather warm, and air tools tend to self-cool.

Or when the tool is mounted on a machine with an arm that rotates
around the work, and a rotating air coupling is a lot easier to rig
than electrical slip rings.

If you have a duty load like that, you need to switch to an electric
drive Cold Saw. Go look on the right column of that drillspot page,
they list one for a little under a grand.