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  #31 (permalink)  
Old 12-14-2009, 06:55 AM
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its a quick and easy way to get straight thru cuts at varying angles on steel of any shape. with a hand held, its far less accurate to cut around and then grind to flush...and slower. I use it far more for off-topic projects.

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  #32 (permalink)  
Old 12-14-2009, 10:54 AM
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I like the Milwaukee cut off saw the blade is a carbide tip blade. Very nice some sparks now and then but does not have all the problems these abrasive type saws do..

works great after 5 years still cutting with the original blade, if HF is so great tell me about it 5 years from now, and please let me know how many blades you've burned through.

I love ''it looks the same'' statement .... that says it all ...

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  #33 (permalink)  
Old 12-14-2009, 04:26 PM
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Quote:
Originally Posted by Old Rotor Flap
Several decades ago manufactures rated electric motor in HP. It was just too basic for the average consumer and therefore it was necessary to find a way to express features in less useable terms.

Enter amp. ratings.

Look at a real motor data plate, like a Dayton motor. Lots of information including HP and amp. ratings and rpm. The consumer power tool market avoids as much comparative information as possible. Consumers who make critical comparisons in search of quality are confused and shouldn't be exposed to tedious details.

Look at the air compressors at Home Depot and Lowes. They're rated at some virtually useless HP number, one that rates it's HP when it's not actually compressing air. I've seen'em rated at 7.5 peak HP. Yet, when you look at the motor (usually Emerson = Ember-soon?) the HP line on the tag says SPL. SPL sounds like another word for Trust Me, which is the only Yiddish I know and it translates to fy. I've seen the same compressor that had the same size Emerson motor where the tag said 5 HP. They must have let one slip through to the compresser company.

Amperage rating is one measure of bearing inefficeincy. A failing bearing will increase amp. draw. Want a higher amp rating for your product? Put cheap bearings or bushings in it.
A HP line on the tag that says SPL means "special". You guys all have good points, but you need to look at the torque the motor is producing to know how good the motor is. A one horsepower motor produces 3 ft. lbs of torque at 1800 RPMs. At 3600 RPMs it produces 1 1/2 ft lbs of torque. That means that a 2 HP motor would produce 3 ft/lbs of torque at 3600 RPMs, and a 4 HP motor would produce 6 FT/lbs of torque at the same speed. The motor manufacturers do fudge the horsepower ratings based on peak amperage draw which is not how to rate a motor because their ratings are not based on electrical fact.

In Vince's example, a 1 HP motor draws 16 amps at 120 volts. At 240 volts, that same motor would only draw 8 amps. It is still doing the same amount of work only at half the amperage draw. That means at 120 volts it would be close to tripping or tripping a 15 amp breaker in the breaker panel just at full running speed regardless of load. My air compressor is rated at 5 "peak" horsepower and runs with no problem on a 20 amp single pole circuit. If you think about it for a minute, that doesn't make any sense. To get the ratings they claim, they lock up the motor and then measure how much amperage is being drawn with the motor completely stalled. That will give you greater peak amperage ratings, but doesn't really tell you how well the motor performs when actually doing work with the saw.
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Old 12-14-2009, 07:16 PM
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Dan that "peak" hp figure will not trip a 20 amp breaker because the breaker is setup to handle sharp quick loads. It may very well draw over 20 amps very briefly, but if it continues past a few milliseconds the breaker will take it out. In industry in large motors we use what is called a slow blow fuse that rides through the inrush current a motor draws when starting.

FWIW, that "peak" HP figure is absolutely meaningless when trying to figure out a motors capacity.

Vince
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  #35 (permalink)  
Old 12-15-2009, 07:32 AM
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Yes, I know Vince, that was my point. Peak HP is meaningless, especially expressed as amps. My 5HP (peak HP) compressor motor is actually about 2 real HP. In any motor application, the amount of torque needed to push the load is what is important.
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Old 12-15-2009, 06:02 PM
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So, SPL means special. That's good to know. I was afraid it meant Suitable Power Lacking. Or, Something Probably Less, or Some People Lie.

I trust we are all in agreement that torque is very important. So important I suspect, maybe that's why it's not listed on the motor data plate or catalog lists.
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Old 12-16-2009, 07:08 AM
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A true 1 HP motor produces 3 ft/lbs of torque at 1800 RPM, irregardless of how many amps it is drawing or what voltage it is being run at. Torque is proportional to speed, so that same motor running at 3600 RPM produces 1 1/2 ft lbs of torque. That same motor running at 900 RPM produces 6 ft/lbs of torque. That's why your drill press can go through more the slower it is running. If you have a true 3 HP motor running at 3600 rpm it is producing 4 1/2 ft/lbs of torque. You can change the torque your motor produces in two ways. You can either buy a motor control to change the speed of the motor itself, or you can change the ratio to the driven load through mechanical means like gears or pulleys.
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