Grinder motor horsepower

Sturubu

Sturubu

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Oct 16, 2010
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I'm sure this has been discussed, but my searches came up dry...

How low has anyone gone on motor horsepower - is it reasonable to try a fractional hp motor on a no-weld grinder (or similar) kit?

Thanks.
 
I would say not, of course I'm only speaking from my personal experience.. I have a 1 1/2hp motor and regret going with it, yeah it gets the job done but there are so many times I wished I sprung for a 2hp.. +
 
1 hp with a 6" drive wheel on a motor that is 3450 rpm the extra speed will eat up that metal .belt speed 5000 sfpm but you may want to controll it with a variable speed drive . if you grind lightly 3/4 hp will get you by for a while . and is much better than using a file and sand paper.
 
I've never used anything but diamond files and stones, so I have no grinding experience. So now for what is probably a dumb question, but where does all the horsepower go - is there that much pressure on the belt, and if so, doesn't it really heat the steel? Seems like with a light touch anything that will move the belt across the steel will work, but obviously this isn't the case.
 
I have been really frustrated with low power of my 1.5hp. Maybe I just got a bad one but it is under powered. So much so, I just bought a 3 HP and will use the 1.5hp for a 9" disc grinder. Most people are very happy with 2HP. My 10" wheel worked pretty well for 1.5hp but the flat platen I could stall too easily.
 
I've got a 2hp on my NWG.
Happy so far, though if i was to make the decision again i'd go for 3hp
 
I agree with those that run a 2HP motor. I have one on my KMG clone and would not want anything less. A 3HP would be nice but the price of the VFD for a 3 HP is what kept me with a 2HP motor. If I were only planning to use step pulleys 3HP is what I would go with.
 
Sturubu said:
I've never used anything but diamond files and stones, so I have no grinding experience. So now for what is probably a dumb question, but where does all the horsepower go - is there that much pressure on the belt, and if so, doesn't it really heat the steel? Seems like with a light touch anything that will move the belt across the steel will work, but obviously this isn't the case.
Click to expand...

The horsepower goes to keeping the belt speed consistent so you have more predictable results.
 
I've got a 2HP DC motor on my GIB, and I can hear it strain when I really lean into a grind ont eh flat platen. But then coming from a 1/3 HP Craftsman 2 x 42, it's night and day! I wouldn't recommend anything less than 1.5HP.
 
pheer327 said:
1 hp with a 6" drive wheel on a motor that is 3450 rpm the extra speed will eat up that metal .belt speed 5000 sfpm but you may want to controll it with a variable speed drive . if you grind lightly 3/4 hp will get you by for a while . and is much better than using a file and sand paper.
Click to expand...

I believe you meant to say 1725 rpm instead of 3450. The 3450 with a 6 inch drive wheel will move the belt @ 10,800 sfm. Smokin.

Sturubu said:
I've never used anything but diamond files and stones, so I have no grinding experience. So now for what is probably a dumb question, but where does all the horsepower go - is there that much pressure on the belt, and if so, doesn't it really heat the steel? Seems like with a light touch anything that will move the belt across the steel will work, but obviously this isn't the case.
Click to expand...
The new ceramic belts are manufactured to operate best with a lot of pressure and higher speeds thats when they cut best. To get the most from the new technology belts you need hp.
David Metzger said:
I have been really frustrated with low power of my 1.5hp. Maybe I just got a bad one but it is under powered. So much so, I just bought a 3 HP and will use the 1.5hp for a 9" disc grinder. Most people are very happy with 2HP. My 10" wheel worked pretty well for 1.5hp but the flat platen I could stall too easily.
Click to expand...
I have two KMG grinders, one is set up with a 2 hp motor the other runs a 3 hp with pulleys. The 2hp is used for lighter work while I grind all bevels and the like on the big guy. You will be pleased with your purchase of the 3 hp motor.
FTO_dude said:
I've got a 2hp on my NWG.
Happy so far, though if i was to make the decision again i'd go for 3hp
Click to expand...
Two is good three is luxury.

There is no substitute for hp, none. With quality sharp belts a grinder that is aligned and enough hp to keep the frustration down, there is nothing you can't accomplish.

Fred
 
As a beginner, I have to agree with Fred Rowe. Modern belts are designed for use at higher pressure to cut cleaner. I regularly use a ½ HP motor on my 2x72 grinder and have made several knives with it. A friend has a 3HP Bader grinder. The biggest difference I notice is that my belts(Yes, I always bring belts to use) last MUCH longer on his grinder. The only logical difference is that I can push harder without slowing the machine. I can perform the same work with the ½ HP motor, it just takes longer and I use more belts.
 
Fred.Rowe said:
Originally Posted by pheer327
1 hp with a 6" drive wheel on a motor that is 3450 rpm the extra speed will eat up that metal .belt speed 5000 sfpm but you may want to controll it with a variable speed drive . if you grind lightly 3/4 hp will get you by for a while . and is much better than using a file and sand paper.



I believe you meant to say 1725 rpm instead of 3450. The 3450 with a 6 inch drive wheel will move the belt @ 10,800 sfm. Smokin.
Click to expand...

Pheer327's post is exactly how my Bee grinder came but it's direct drive

A 1 HP 3400 rpm motor on 110v draws 12 amps - just fitting a 15 amp breaker at 80% load
a 1 HP 1740 rpm motor draws more current and will NOT safely fit on a 15 amp breaker (on all the motors I could look at)

I learned to grind with a light touch.
A VFD is a relly nice upgrade.

rpm x (diameter of wheel x pi) / 12" per foot & direct drive with no pulley ratio change, or x the ratio of the pulleys

3450 rpm x ( 6" wheel x 3.14 ) / 12 = 5175 surface feet per minute

That's how I figure out SFM,I'm not sure how you got more than double that- unless you are also including step pulleys.



If using a NWG, with stepped pulleys you will have to take into account the ratio of a step pulley set

234
432

Low speed is 1/2, middle is direct and high speed is 2x



This is how I would setup a lowest cost NWG -

1HP 3400 rpm motor (to get max HP on a normal outlet)
step pulleys 2"3"4"
and then to get the belt speed down again a 3 " drive wheel
 
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Rob at knifemaker.ca uses 2 BEE grinders at 1 HP each and he says he's happy with those. I went for the 2 HP variable model, and I'm pretty happy with his power, you have to really push to slow it down, much harder than I would be pushing while grinding a knife bevel (at least at my level of experience). More is better for sure, but I think with the right motor you can do pretty well with 1 HP.
 
Folks must realize that not all motors are really what they say they are either..Lots of guys end up with take off motors that say 1 1/2-2 hp but only draw 8 amps(WHich means it aint 2hp)..We had a thread a while back where some of us did the math on amps drawn vs rated HP and such..Heres a post I made about it a while back..
--------------------------------------------------

.
I think that some newer motors are rated on "peak" power, not continuous. It takes "x" ammount of amps to get "x" ammount of watts to matter what you do.No motor can do otherwise.Volts*Amps=Watts, Watts/Volts=Amps
Heres a formula I found..
voltage x amps x efficancy
hp=----------------------------
746
Meaning if you have a motor that has a 70% efficancy rating, uses 125v and draws 9 maps its hp would be 1.0 hp..
.
Baldor uses the formula voltage x amps x efficancy x power factor= output watts..baldor does list thier efficancy and power factor on the nameplate, or they did anyway..
heres a link I found about air compressor motor ratings...
http://www.asedeals.com/air_compressor_faq.pdf
.
Most every website I found uses a loose guideline of 10 amps per HP on 115v and 5 amps per hp on 220v..
 
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1thru10

You are, of course correct. I was applying his comment to my own machine, which runs a 2-3-4 pulley system and a 6 inch drive wheel.

Thank you for posting the correction.


Pheer327 I should have read your post a second time before commenting. My apology, Fred
 
I use a 1 1/2 HP Leeson Farm Duty motor. It does fine and doesn't bog as long as the drive belt is tight. If it gets loose, it will bog down.
Scott
 
My new grinder has only a 1 HP 1740 RPM farm duty (enclosed) motor on a 6" drive wheel and hooked to a 20A circuit. I have no idea how it will perform, but I expect it to perform better than my 1/3 HP motor on the HF 1X30 sander.
 
I have used 2x72's with 1, 1.5, 2 and 5hp motors. The 1 and 1.5 would bog easily when grinding with the flat platen, the 2hp would run well but I could still bog it down unless the belt was very tight. We need to keep in mind that while using the flat platen we are essentially creating a brake. The pyroceram glass helps reduce friction thus reducing the braking effect. You can get by with a lower HP motor using the glass backer on your platen. I have to say the 5hp single speed worked much better for hogging bevels and profiling.

I now have a 2 motor set-up. I have a 2hp run off the VFD for fine work. Then I have the 5hp that I run single speed for hogging. I just have to switch out the belt and away I go. With the 5hp I cannot bog the grinder down with even very heavy pressure on the flat platen. Many feel the 5hp is over-kill, I LOVE it.
 
A good point was made above about keeping the belt tight. I think it's common enough for people to either have a drive belt or the grinding belt too loose, which enables slipping on the drive pulleys or the drive wheel. It's not always apparent that this is the case, after I switched to a heavier belt tension spring on my 3hp grinder it runs much more stably.

Something I've seen done but not tried myself is hooking two fractional motors rated at the same speed and with the same size pulleys onto the same drive belt, i.e. two motors on top of each other both driving the same shaft pulley. I've heard this can work for combining say two .5hp motors into a 1hp. motor.

I think with a true rating of 1hp, tight belts, and not absolutely dull grinding belts, a 1hp motor will get you by fine if that's what you have. If you have a choice of motors, I'd say get 2hp+.
 
I run a 1.5 hp 1725 RPM motor I got from Wayne Coe.

It never bogs down and I am a big man and can push hard. The only time it even thought of slowing down was with a 1.5" square bar of 6061-T6 and I was trying to bog it down . It only phased it for a moment of extreme pressure.

I found the key is a motor with good torque and high amps. As mentioned before if you are running a 1 or 1.5 HP motor that is only 8amps it will be a dog.

So always consider the amps when buying a motor
 
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