# circular saw rpm-is that the motor or blade rpm?



## [email protected] (Jan 22, 2006)

Circular saws have rpm rated on them, but I need to know if that is the blade or the motor? The project I am doing involves attaching a pulley to the motor and rpm's is absolutely important.


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## Teetorbilt (Feb 7, 2004)

What are you attempting to do? It sounds rather dangerous. Most circular saws are direct drive so that the two are the same. In the case of a worm drive, the motor RPM will be listed on the motor and the shaft RPM listed seperately on the motor plate or saw body.

Please, PLEASE don't tell me that you are attempting a DIY table saw.


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## robertcdf (Nov 12, 2005)

I would think that a circ saw motor RPM would be way to high to use for much other than a saw. Or maybe a fan. I would like to know what you are planing on making


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## [email protected] (Jan 22, 2006)

with the blade taken off and saw housing mounted to bench, i am mounting a pulley to turn a alternator....alternator mid range rpm is 4500


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## Teetorbilt (Feb 7, 2004)

Have you checked the alt. horsepower rating under load? It sounds as if you are assembling some Rube Goldberg contraption to accomplish........what?


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## [email protected] (Jan 22, 2006)

I know the HP needed....I am testing alt's


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## slickshift (Aug 25, 2005)

Unless it's a worm drive, the motor and the shaft and the blade rotate at the same RPMs


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## Teetorbilt (Feb 7, 2004)

I'm still wondering why? What are you trying to accomplish?


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## DangerMouse (Jul 17, 2008)

i guess we'll never know......


DM


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## nap (Dec 4, 2007)

DangerMouse said:


> i guess we'll never know......
> 
> 
> DM


has boredom set in DM? Not like you to respond to 3 year old threads.


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## DangerMouse (Jul 17, 2008)

naah, i just found this thread when i was looking to build my own table saw from a circular saw and a few drywall screws to hold it to the table... just down the one side so it hangs there, you know.
kinda funny this never got resolved though.

DM


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## skymaster (Jun 6, 2007)

Tho a really old post based on his screen name: IE Airpower, he should know that the rpm is the same as shaft speed, but increases dramatically as hou expand out to the "disc" that is rotating IE tip speeds on either props or saw blades.


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## ponch37300 (Nov 27, 2007)

I did this when I was younger and into car stereos, but not with a circular saw. I used a 110 motor and a high output alternator to make a power convertor to power my amps out of the car for testing. I used different sized pulleys till I got the rpms right for the alternator. 

As far as the table saw from a circular saw I also built one of those before I could afford the real thing. I used my router to make a spot for the base plate to recess in the table and used some screws counter sunk in the plate to attach it. I just used a homemade fence so it was kinda a pain to adjust but worked.


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## Thurman (Feb 9, 2009)

I noticed the old post also, but wanted to share this. When you are asking about the "speed" of a circular saw blade versus the "speed" of the circular saw motor, I am thinking a hand held circular saw. The speed, or RPM, of the motor and the blade are the same. NOW, if you are talking about a table saw, with direct drive, where the blade is directly attached to the motor of the table saw, it's still the same, RPM for RPM. A blade driven by a motor/pulley attachment is different and we'll get to that. Here is your problem, to me: No one mentioned Surface Speed in Minutes vs. RPM. A whole new ball game here. IF, note the IF, your motor is turning say 1000 RPM, and you have a 10" blade, the area where the mandrel of the motor attaches to the blade is going to turn 1000RPM's as the motor all day long, and yes the outside of the blade will be turning 1000 RPM's also. BUT, if you measure the circumference of the blade, a 10" blade will be app. 31.7" in circumference, which means that the outside of this blade will travel 31.7" with each revolution. Therefore with 1000 RPM's you will have 31,700" or app. 2641.6 Surface Feet per Minute (SPM). So, I hope you see that if you get into belt drives with different pulley diameters you will get different SPM's as you change pulley diameters. Having worked with manufacturing alternators I would highly recommend that if you are going to build a "test stand" you stick to that 4500 RPM range FOR THE ALTERNATOR. IF you are using a circular saw to do this, I highly do not recommend this approach, get you a motor that can be bench mounted. I won't tell you that we tested our units at two different speeds, low and high and what those RPM's were, it will scare the hell out of you. Thanks, David


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