HorsePower Curiousity

Jack O'Neill

Jack O'Neill

Gold Member
Joined
Nov 15, 2007
Messages
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I keep reading here how everyone is telling everyone that you need at least a 2 H.P. motor to run a grinder . This baffles me . I know in life that at times if some is good then more is better and I know it can relate here to our craft with motors and grinders . BUT - what baffles me is why spend $350.00 when $150.00 will work , especially when everyone is looking to save a buck .

I ask and present this question because I have been running a 2x72 grinder since 1992 with a 3/4 h.p motor with step pulleys and , and have never yet stalled or bogged this machine down and have a couple 100 knives behind it .

I guess I will be answering my own question here because when I order a new grinder I will go with a 1 or 1 1/2 H.P. motor to be on the safe side . But I have been curious .
 
interesting. i have wondered why the need for so much power. i havent built my NWG yet tho so i dont have a clue and i am looking forward to this thread!

thanks for posting!

jake
 
it is a good question...

I have 1 hp, bogs down even running a 3.25" dia drive wheel @ 3450 rpm

thinking of switching to 5 hp diesel on lineshaft

but i grind a lot of swords
 
Aspects of your grinding style come into play. Light grinding pressure or lower SFM are less likely to bog a motor down. I bog down a 1HP easily. A 2 HP is fine for me, though I don't press that hard. A high speed grinder (5000 SFM or more) is geared in a way that the motor is at quite a mechanical disadvantage, and they require quite a bit of HP. 3HP is not unreasonable for some folks who really lean into a high speed belt.

My first production mill had a 7 HP spindle. I thought that was plenty (sounds like a lot doesn't it?). I eventually got to a 30 HP mill, and going back to the little mill makes me wonder how I ever got anything done. You unconsciously adapt to the abilities of your tools. If you used a 2 HP grinder much and went back to your 3/4, I think you'd be surprised.
 
I have a KMG with a 1.5hp and I can stall it out. It will take the steel off nicely but If I am doing a full flat grind and lean into it it will stall out. Grinding in the distal taper will do it also.
 
I've stalled out my 2x72 1 hp grizzly many times. My 2 hp KMG just laughs at me for the most part.

There's not many here that will say you HAVE to have a 2 hp motor for a grinder. Most agree that 1 hp is the bottom power limit for the vast majority of people. 1.5 hp works better, and 2 hp is the cat's meow. Above 2 hp and you're just showing off ;) :D.

I think the other Nathan nailed it on the head. It's all about how you grind. If you grind heavy, a 2 hp or above motor is called for. If you're a finesse grinder, you can get by with a 3/4 hp motor. Most people need at least a 1 hp.
 
I guess I should give a little more info . Based on the tachometer and the 2 speeds I feel comfortable with . When I do the profile hog grinding the machine is running at around 3500 sfpm and for the blade grind I am at about 1150 sfpm . I do push hard on the hog grinding . I was wondering how much the belt drive step pulleys come into play . On my disc grinder I will stall out a 1/2 h.p 1725 rpm but my little 1/3 h.p 1140 rpm will run all day .
 
silver_pilate said:
I've stalled out my 2x72 1 hp grizzly many times. My 2 hp KMG just laughs at me for the most part.

There's not many here that will say you HAVE to have a 2 hp motor for a grinder. Most agree that 1 hp is the bottom power limit for the vast majority of people. 1.5 hp works better, and 2 hp is the cat's meow. Above 2 hp and you're just showing off ;) :D.

I think the other Nathan nailed it on the head. It's all about how you grind. If you grind heavy, a 2 hp or above motor is called for. If you're a finesse grinder, you can get by with a 3/4 hp motor. Most people need at least a 1 hp.
Click to expand...

So I guess I'm a finesse grinder:) I like that and you are correct , I do go slow. I'm in no hurry and feel more comfortable that way and heck , the wounds are not as bad . Good Lord I would hate to see what my knuckes and fingers would look like at a 5200 sfpm :jerkit:
 
sorry to sidetrack this thread a little, but how much does voltage and Hrz come into play in this equation? eg. is a 2hp 220 - 240 volt motor harder to stall than the equivalent motor in 115v? i'm running a 1.5 hp 3phase (415volt in Australia) of a VFD and cant even come close to stalling my KMG clone.:thumbup:
 
One thing I thought I should bring up is that stalling out a motor in a grinder has a lot to do with what you're pressing it against. If you're pressing against a wheel, it won't stall as easily as if you were against a flat platen.
 
Boilermaker , you are right on the voltage , I am wired 220 and a big difference over 110 .
I'm liking this thread .

And Go Mike , baby child :D No insulate intended , I am old :rolleyes: Very good point .
 
Oneill, remember when you first got a 2x72? Remember the difference between that and whatever little grinder you might have used before? Well when you get a bigger HP motor with maybe a faster belt speed it is like that all over again :D.
 
Jack, I'm running a 1 1/2hp Baldor farm duty motor on my KMG ansd I can stall it out on the flat platen. When this motor finally goes democrat I believe I'll go with a 3 hp. BTW, I have step pulleys and can stall it on hi.
 
Flat grinding big, wide blades needs lots of HP. Grinding on a contact wheel takes less HP.
I have smoked a 1.5 HP variable Lesson and can easily stop my 2 HP variable KMG with it running wide open.

I want 5 HP for hoggin :D
 
Don Hanson III said:
Flat grinding big, wide blades needs lots of HP. Grinding on a contact wheel takes less HP.
I have smoked a 1.5 HP variable Lesson and can easily stop my 2 HP variable KMG with it running wide open.

I want 5 HP for hoggin :D
Click to expand...

Don, you should look into a Bader Space Saver, 3PH 5HP motor with a 6 inch drive wheel, you can stand on the thing and you won't even hear it wind down :D.
 
boilermaker said:
sorry to sidetrack this thread a little, but how much does voltage and Hrz come into play in this equation? eg. is a 2hp 220 - 240 volt motor harder to stall than the equivalent motor in 115v? i'm running a 1.5 hp 3phase (415volt in Australia) of a VFD and cant even come close to stalling my KMG clone.:thumbup:
Click to expand...

As long as a motor is true to its horsepower rating, voltage (if it remains stable under load), line frequency, or phase should not mater to the work at the end of the motor shaft. So a 1.5 HP, 120 V, 60 HZ, 1phase motor here in the States should do the same work as a 1.5 HP, 415 V, 50 HZ 3 phase motor in Australia. Service factor (SF) is a consideration when you are asking a motor to do work beyond its rated horsepower. So if you are using an 1800 rpm motor and gearing it up through your pulleys to run a higher grinder shaft speed, then a 1.5HP motor with say a 1.65 SF will run longer under the same load without over heating than a 1.5 HP motor with a 1.15 SF.

I am sure that there are people here that understand electric motors and the way they work far better than I do. My knowledge of them comes from working with pumps for the last 24 years and is accurate as far as it relates to the work they do in that application. I do however think that the understanding gained there translates well to this discussion.
 
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from what I'm reading here, from everyone's kind reply , when I can afford to replace this dinosaur I better kick up my H.P. choice . I wonder , since my 8" contact wheel is my drive wheel , how much this may factor in to the lack of stalling or I'm just wimpy and don't press hard enough .

Thanks everyone for your input .
 
techna said:
As long as a motor is true to its horsepower rating, voltage (if it remains stable under load)
Click to expand...

This is a good point. If you feel you don't have enough power make sure to use no extension cords, or only a suitably large one. Also make sure the building's wiring and service are up to par. Checking voltage drop under load may be a good idea. Going to a larger motor may not be as necessary as providing the existing motor suitable power.

Alden
 
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