Circular Saw Motor for 2x72 grinder?

Splat

Splat

Joined
Nov 19, 2006
Messages
907
Since my father's passing last November I've been slowly cleaning out my folks' garage. It's amazing how much tools and ..... well, junk, a guy can accumulate! :eek::) I'd give it all away to have my father back... but anyway, I found about 4 circular saws. Two have 2hp motors with 5/8" shafts. Aside from possible mounting issues, would it be possible to use one of these motors for my NWGS? IIRC they're 5000rpm so I'd have to use a few pulleys for reducing the speed. Other than that.....? Thanks.
 
Last edited:
I'm really sorry for your father.
2hp is ok for a belt grinder and instead of some pulleys you could use an inverter. but i'm sure someone with more experience will give you better advices.
take care
 
Yes, you could make that work, but I wouldn't. That kind of motor is probably a brushed AC motor and won't last very long when used in an application where it will be running loaded for extended periods. I expect a few hours of grinding to end in smoke...

A surplus 1700 or 3400 RPM induction motor can last for thousands of hours, are quiet, and are inexpensive used.

One upside to using a saw motor is you could control the speed (to some degree) with a large dimmer switch. That won't work with a regular AC motor.
 
The rating on such tools is developed HP, and not the same as the HP rating on plain motors. Ever noticed how a 3HP router or vacuum only draws 7 amps? You can't use that motor to run a grinder. Sorry to disagree with the above folks, but it will not work. What you will get is smoke.
 
bladsmth said:
The rating on such tools is developed HP, and not the same as the HP rating on plain motors. Ever noticed how a 3HP router or vacuum only draws 7 amps? You can't use that motor to run a grinder. Sorry to disagree with the above folks, but it will not work. What you will get is smoke.
Click to expand...

interesting! I always wondered how a dust collector can have 1500W or something like that. Can you explain what's the difference between "real power" and "developed power"?
 
A real horse power was originally defined as the power required to lift some specific weight some distance in a particular time. It worked out to about 700 watts of energy delivered. So a electric motor that is 100% efficient (they aren't) that consumes about 700 watts would be a 1 hp motor.

The reality is, most motors consume closer to 1000 watts for each HP delivered. So what is up with a 6 HP shop vac that only uses 10 amps of 120? There are deceptive ways of "calculating" HP such as looking at maximum torque (at stall speed) and maximum no load RPM and calculating a value. Or, they can look at maximum amp draw at stall and tell you how many HP of electricity are being consumed. Not the same thing as real delivered HP rating. Which is why a real 5 HP motor is 10 inches around and weighs 50 pounds and the shop vac that makes "6 HP" is a tiny little thing.

That "6 HP" shop vac that is rated to draw 10 amps of 120 is 1200 watts, meaning it is about 1 HP delivered.

That said, plenty of old saws and routers etc gave real HP figures. I have a 2 HP router that draws 15 amps at full load. 15 X 120 = 1800/700= 2.5 HP power = it probably delivers 2 real HP.

However, today manufactures play HP games. It isn't just limited to saws and shop vacs. I use a "30 HP" Haas VF2SS mill that is probably only good for 15-20 real HP in use.
 
One horsepower is 33,000 foot pounds of work per minute...or in electrical terms 746 watts.

Most motors are rated at 1800 RPM. Motors that run at higher speeds are calculated in such a way that they show a higher HP rating than is real. Look at your lawn mower engine and then look at your shop vac motor.....do you think that the shop vac would turn that 22" mower blade?

I just googled up a couple of shop vacs, and a 2.5HP vac draws 6.3 amps. That is 2.5 amps/HP. But, at 120 VAC, a 1HP motor draws 6.2 amps. So, you see that the shop vac is not really a 2.5HP motor. What they do is use the Peak developed HP ,which is some sort of measurement that combines no-load RPM and the current draw ( plus a serious amount of fudge factor) and arrives at a much higher number. When you walk down the isles at the super box store, all your brain sees is the great big 2.5HP printed across the box front. If you want to be a smart shopper, turn the box around...hunt all over the small print...and find the current draw. In small type you will find 6.3 amps.
 
Thank you guys for responding. Looks like I'll be biting the bullet and getting a real motor. I'd rather be building other things than constantly rebuilding my grinder due to a crap motor.
 
You must log in or register to reply here.
Back
Top