Mixed opinions - what size motor for 2x72 grinder

H

hammerface

Member
Hey everybody - I've researched this until I'm blue in the face and I'm no further ahead and more confused than when I started. I'm gearing up for a NWG build and have everything except the motor. Here's the age old question - how big of motor do I really need???

Many say 1.5 min or 2HP and up ideally. Yet many say 1HP is plenty and can't understand why others bog down machines running a 1 or even 1.5HP motor.

Is it better to spend more on say a quality brand motor (ie:baldor or leeson) that is slightly smaller (say 1HP) versus buying a cheaper no-name motor that is 1.5HP?

I guess I'm just confused as to why some say 1HP is lots of power and others disagree. I want to keep my costs relatively low and may have a line on a 1 HP Baldor however I don't want to underpower my machine and regret my decision.

I know this has been hashed about many times but any additional insight would be greatly appreciated before I drop the coin on a motor for this thing.

Thanks in advance everybody! :D

And yeah, Tracy recommends a 1.5 so that definitely counts for a lot cause he designed the thing! I'm not doubting him whatsoecer, I'm just over-researching and wondering what my best option is at this point in time :)

Al
 
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Mr Hammerface.:D Nice name2thumbs
I have a 1.5 horse and never really needed more.
I have not used less motor but I can lay into a 8inch contact wheel with a 60 grit belt and remove some metal in a hurry without bogging it down.
If you already have the smaller motor try it out.
I will say Tracy knows his stuff on these and has probably tried every size motor and he recommends the 1.5.
 
If you have a choice go for the bigger one it's a lot cheaper than buying a second motor if you find the smaller one just dosen't do it for you.
 
I run 2hp and also have never bogged down. As far a motor power goes I guess it's like the old saying: it's better to have and not need than to need and not have. Then again some things are decided by cost. I would have prefered to have a motor that turned at about 1800rpm but I couldn't find one that was affordable at the time I was assembling my grinder so I had to settle for one at 3600rpm. Very usable but not optimal.

Doug Lester
 
At the moment I have the option of:

a) a hardly used 1HP baldor for about $170 CAN shipped

b) a 1.5HP farm duty motor from Princess Auto for $225 incl tax - not sure on brand - marathon maybe?..

http://www.princessauto.com/farm/el...-hp-farm-duty-electric-motor?keyword=hp+motor

c) Or a 1.5HP industrial duty motor from princess auto for about $260 incl tax.

http://www.princessauto.com/farm/el...p-farm/industrial-duty-motor?keyword=hp+motor

All motors are 1 phase, tefc, 1725rpm....

:confused::confused::confused:

thanks for the input guys, I really appreciate it 2thumbs

For those of you that have bogged down a 1HP motor what exactly were you doing to bog it down?
 
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You will see lot's of different opinions on this for a lot of reasons.

First, all 1.5hp motors do NOT pull the same. Some just SUCK and wouldn't provide the torque ft/lb's a good quality 5/8hp motor would. This is almost always overlooked.

Some motors are very efficient using high quality components that will give a lot more bang for the buck. So when you hear one guy using a 1hp motor and saying he can't stop it and another guy saying he stops his 1.5hp motor they could both be right.

Also, is the grinder a 2 wheel, 3 wheel or 4 wheel set up? A 2wheel setup eliminates the drive belt so that is very efficient in transferring power. A 4 wheel set up has more wheels to move. A 1hp might power a 2 wheel setup and dog out on 4 wheel setup.

When a guy says he can stop his 1hp (or 1.5hp or 2hp) grinder, is he flat grinding or on contact wheel? I can stop my 1.5hp Baldor DC motor (this is a good motor with high efficiency rating) when flat grinding or at least pop the circuit breaker. I can't do that when grinding on the 8" contact wheel.

I can stop it when I am grinding on the 14" wheel though. Which brings us to mass. The more mass you have in wheels, the more horse power you need to get it moving and keep it moving. The advantage to all that mass is it acts as a flywheel to keep things moving along when you are grinding.

My disc grinder sports a 9" disc and is only 3/4hp. I'm not sure I could stop that if I even tried. It is very strong. It is a 3phase frequency drive motor.

Sooo....a 1hp may be a very good choice for a 2 or 3 wheel set up that is contact wheel grinding only. A 1.5hp is probably better for a 3 or 4 wheel setup for all around. A 2hp is probably good for high volume flat grinding.

Personally, I think a 1.5hp is the minimum you want for a typical 2"x72" grinder. I talk to a lot of grinder builders and those that went smaller than 1.5hp ALL want to go bigger - when they can afford it. I've never talked to anyone that had a 2hp that said it was too big.
 
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Thanks for your input Tracy - that is what I was wondering. If a lower HP rated, but better build brand name motor might out perform, or be equal to, a higher say 1.5 HP rated cheaper, no-name motor.

I understand the belt-driven 4-wheel set up would require more juice. Never thought about the difference between flat grinding and using a contact wheel - thanks for that.

I'll keep hunting - I swear 1/2 the fun of this project so far is the research and hunting down the parts (yes, I may just be a big geek..lol)

Have I mentioned that

luvsite1 yet? :)
 
If you intend to grind fixed blades go with a 1.5 or more. The 1 works well for me on two grinders but I am only grinding for folder parts. When I made fixed blades, I had a 2hp motor on the single grinder I owned. I removed the ihp that was on it. Frank
 
Just wanted to add some of what I know about motors, I would like to clarify a few things. Horse power is a measure of work not torque! and torque is what keeps you from bogging a motor. Horse power is a calculation of how much work can be done in a given amount of time. This means that a 3600 RPM motor Rated at 1 HP will have less torque (incorrectly referred to as power) available then a 1 HP motor rated at 1800 RPM. This is because the faster turning motor can move a lighter load but faster resulting in equal work. This can be corrected using pulleys so either motor can be used if final speed is equal then torque will be equal. The difference that you will notice in motors is in the slip. Look for motors rated at as close to 1800 RPM's or 3600 RPM's as possible, as these are perfect values related to the number of poles. A 1750:D motor will bog less then a 1650:( due to efficiency and quality of construction. When VFD's on AC motors or speed controller on DC motors things will change a bit, but the controllers will generally maintain constant torque. which is just what you want.2thumbs So that means I would run a disc grinder directly with a 1750 motor but a belt grinder I would add a VFD to maintain torque at higher than base speeds. By the way if buying a motor new I would go with the 1.5 HP. You will probably never need it all but you wont be be wishing for more either.
 
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I'm going to jump in on this because I have a very strong opinion on it. ;)

You Cannot Have Too Much Power

There. I said it. And I mean it! I have a 1.5 hp variable speed Baldor DC motor on my BIII. I can kill it in a heartbeat tapering tangs; in fact I always do - it takes me a long time to adjust pressure to the point the motor can hang for long term work. I would never buy anything less than 2 hp for flat grinding, and would prefer 3 hp just because I'd want the certainty. When you get in the groove, the last thing you want is your motor to quit.
 
Hammerface, I would really like to hear back from you when you get a motor and what you think of the brand that you bought. And how well the size you bought suits your needs. Please let us know. I am sure there are a lot of people like me who are slowly collecting parts for a NWG.
 
I have to agree with Dave on this one......again, You can't have TOO MUCH motor.

Personally, I have a 3hp variable DC motor on my KMG, while my Square Wheel grinder has the factory 1hp/1725rpm motor. The Square wheel is a different machine, depending on if you have it wired 110V or 220V. For years, all I had to work with was 110V, but when the KMG came along, it gave me the incentive to install 220v. I then re-wired the 1hp Square Wheel for 220v, and I was shocked at the difference. When it was wired for 110v I could easily bog it down, but after wiring it for 220v, it was almost as if I had change the motor to a 2hp! My opinion is to go for at least a 2hp motor, and wire for 220v if at all possible.
 
In my garage are two 5 hp motors. Alas, they're 440v, 3 phase motors, so I'm in no position to put them to work. Always thought if I ever built a press I'd have power. Still may some day. But think the grinder you could drive with one of those bad boys! :D Woo-Hoo!
 
ddavelarsen said:
In my garage are two 5 hp motors. Alas, they're 440v, 3 phase motors, so I'm in no position to put them to work. Always thought if I ever built a press I'd have power. Still may some day. But think the grinder you could drive with one of those bad boys! :D Woo-Hoo!
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This reminds me of a government auction I was at one time and there was 3 600HP electric motors that sold for $300 ea. I would have bought one to salvage the copper out of but there was no fork lift to load it with. Those things would dim the lights in your shop. LOL

My KMG has the 1.5HP due to power limitations. If I had 220v in the shop I would definitely have gone 2HP. Mine is a Leeson 3 phase that runs with the VFD controller on 110v single ph. straight from Beaumont. It is smooth and strong. I can't see being able to stop it if I'm being careful grinding a knife. I suppose I could lay into it and stop it if I really wanted to.
 
ddavelarsen said:
I'm going to jump in on this because I have a very strong opinion on it. ;)

You Cannot Have Too Much Power

There. I said it. And I mean it! I have a 1.5 hp variable speed Baldor DC motor on my BIII. I can kill it in a heartbeat tapering tangs; in fact I always do - it takes me a long time to adjust pressure to the point the motor can hang for long term work. I would never buy anything less than 2 hp for flat grinding, and would prefer 3 hp just because I'd want the certainty. When you get in the groove, the last thing you want is your motor to quit.
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:confused: Wow a DC 1.5 HP motor should be any thing but easy to bog even with a big flat wheel. I am curious about your controller. Does it have IR compensation adjustment? If so you might try tweaking it a bit. It might be worth wile for you to upgrade your controller. A DC motor with good controller will maintain constant speed very well and the lower the speed the higher the torque, at least in theory. Of coarse you could just be over powering the motor:D
 
I have a NWG and I found a 1.5 baldor I dont hink I could bog that motor down, Better quality motor = more power, I have a 4"x36" belt sander with a cheap noname 1.5hp I can bog it easy, go with Quality motor 1 hp baldor should be fine.
 
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