What size motor

B

bondy

Joined
Mar 19, 2008
Messages
212
Hi fellas im an hobbyist maker from england and iv pretty much finished building a 2x72" belt grinder,and id like your opinions on motor size 1.5 2hp. iv only got single phase electrics .
and how much better is variable speed than a 3or4 step pulley system.
looking forward to your replies thanks:thumbup:. Warren
 
I went from a 1.5 hp with step pullys to a 2hp Var speed and it is a dream come true.
 
Variable speed is a big improvement. It is great to be able to make the belt go real slow when doing your fine finish work. With step pulleys you get some speed change, but, not near the range and with variable speed it just takes a couple seconds, with pulleys, even with a hinged setup it takes a bit of time. I loved it so much on my grinder I got a VFD and a 3 phase motor and set it up on my milling machine to keep from using the factory step pulleys on it for speed adjustment.
 
Shoot for as much horse power as you can afford. There is nothing more frustrating than an underpowered grinder.j
You can always slow the SFM down by using step pulleys or a variable speed control; but you can not make up for a lack of HP driving the belt.
I run a 3HP motor with a three step pulley system on my main grinder.
The motor is attached to a hinge that allows for full V belt tension against the pulleys. No belt slip is what you are shooting for.The machine can not be slowed down no matter what pressure is being applied.

I would reference the above by adding; I was a teenager in the 60's and muscle cars are in my blood so that affects how I view machinery.

Good luck with that new grinder and have fun, Fred
 
Cheers guys:thumbup: looks like at least 2hp motor then and deffo vary speed thank you:thumbup:.
 
Fred.Rowe said:
Shoot for as much horse power as you can afford. There is nothing more frustrating than an underpowered grinder.j
You can always slow the SFM down by using step pulleys or a variable speed control; but you can not make up for a lack of HP driving the belt.
I run a 3HP motor with a three step pulley system on my main grinder.
The motor is attached to a hinge that allows for full V belt tension against the pulleys. No belt slip is what you are shooting for.The machine can not be slowed down no matter what pressure is being applied.

I would reference the above by adding; I was a teenager in the 60's and muscle cars are in my blood so that affects how I view machinery.

Good luck with that new grinder and have fun, Fred
Click to expand...

hay Fred i also have mine on a hinge but if i put alot of force on the belt the motor will lift up and the pulleys will slip. i have been thinking about putting a spring on it to keep it down. right now i have a block of steel leaning on the base plate on the motor thats closest to me to keep the motor down.
 
Got a 2HP with variable speed on my KMG and it's the cats meow! :D
Of course you need 230V. 1.5HP is pretty much the limit with 115V.

Patrice
 
Since all you got is 115v go with the 1.5. I use a 1.5 dc motor with a speed control. You can buy the speed controls as a board with no enclosure and wire it yourself and mount it all in a plastic box, you can save quite a bit this way.You can also buy used dc speed controls off ebay.I bought my motor and speed control from Surplus Center for around 300$.You could also get a 1.5 hp 3phase motor and a VFD but its going to cost more.
 
JTknives said:
hay Fred i also have mine on a hinge but if i put alot of force on the belt the motor will lift up and the pulleys will slip. i have been thinking about putting a spring on it to keep it down. right now i have a block of steel leaning on the base plate on the motor thats closest to me to keep the motor down.
Click to expand...

JT

Something is amiss here; this should not be happening. It sounds to me like the hinged motor is to close to the pivot point. Try a slightly longer belt.
If you can depress the belt from the top with your finger and make the motor move, the motors position needs shifted a little.

Fred
 
This is my KMG setup:

setup.jpg


It is 2HP single phase. Using the 4 step pulley this way you don't need a hinge setup and you get a good speed range. This is 1000 SFM (slooow) to 5000 SFM (faaast). To change speeds you roll the belt onto the smaller cog, then roll the other side up onto the larger cog, the developed belt length is the same between for all four speeds. It takes only a few seconds to change speeds and it has never slipped on me.

I'd say that 1 1/2 is the min power you'd want.
 
I'm also building a kmg clone and will be looking at motors soon. I can't afford a VFD, and will be trying pulleys.

To determine my pulley ratios, I'd like to know what you guys think are the best belts speeds?

This is 1000 SFM (slooow) to 5000 SFM (faaast)
Click to expand...

Would you guys generally agree that these are the min and max speeds needed for a 72" kmg?
 
I have a 1hp motor on my kmg with pulleys and it works fine for now. I am planning to upgrade to a variabole speed motor one of these days.
 
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