Diy belt grinder - need help with drive wheel size

[taviii11]

Hi friends! My name Is salvador. Im currently building a belt grinder for knife making and general purpose. I Will post some photos of the machine.
The project Is almost finished but i need to build a drive wheel.
My specs are

3 phase - 2hp - 1435 rpm motor - 50hz (4 poles i Guess)
Vfd 2hp single phase to three phase
3" belt width

I was thinking on a 6" wheel but this Is my first grinder and i would like some input from More experienced users.

---

 

[pafka]

Hello Salvador, I believe for grinding steel you'd want around 20 m/s belt speed, but having more would not hurt since you have a VFD and can slow things down.
Using this calculator: https://www.burrking.com/sfpm with 6" wheel and the 1435 RPM motor you'd have about half of that. With 10" wheel you'd have almost 20 m/s, but that may be a big wheel - it may be worth it going for a faster motor.
Other will correct me if I'm wrong I'm sure.

Pictures have to be linked from 3rd party sites, like imgur.com or similar - upload them there and you'll get a link that you can add to your post.
edit: nice grinder

 

[JoeBusic]

8"/20cm wheel should do. Not bigger as it's only 2HP motor. Not smaller than 6". For occasions where some speed is required, VFD can speed up the motor to 200% as it uses the same bearings as 2 pole motors.

 

[taviii11]

Hello Salvador, I believe for grinding steel you'd want around 20 m/s belt speed, but having more would not hurt since you have a VFD and can slow things down.
Using this calculator: https://www.burrking.com/sfpm with 6" wheel and the 1435 RPM motor you'd have about half of that. With 10" wheel you'd have almost 20 m/s, but that may be a big wheel - it may be worth it going for a faster motor.
Other will correct me if I'm wrong I'm sure.

Pictures have to be linked from 3rd party sites, like imgur.com or similar - upload them there and you'll get a link that you can add to your post.
edit: nice grinder

Thanks pafka! I need to use this motor cause i runed out of budget.

8"/20cm wheel should do. Not bigger as it's only 2HP motor. Not smaller than 6". For occasions where some speed is required, VFD can speed up the motor to 200% as it uses the same bearings as 2 pole motors.

I designed the grinder thinking i would use a 4" wheel with a fastest motor. Lately i decided to use this old motor that was laying around im my shop. I recently put new bearings and grease on it.
The thing Is im seeing that i can Fit a 7" wheel Max . If i go for a bigger wheel the extending arm touches the Main body.

Im interested in the method of speeding up the motor with the vfd. Motor runs at 50hz so for a 200% boost as you say it means i need to "overclock" the motor to 100hz? Is that right? Does that boost pose some danger for the motor?

Thanks for the help both of you

 

[JoeBusic]

Im interested in the method of speeding up the motor with the vfd. Motor runs at 50hz so for a 200% boost as you say it means i need to "overclock" the motor to 100hz? Is that right? Does that boost pose some danger for the motor?

No danger. They are built the same from 2 pole to 6 or more poles. More poles is just to make it have more torque on lower speeds. So, mechanically speaking a 4 pole motor at 200% is a 2 pole motor at 100%. It's just heavier from more copper.

 

[taviii11]

No danger. They are built the same from 2 pole to 6 or more poles. More poles is just to make it have more torque on lower speeds. So, mechanically speaking a 4 pole motor at 200% is a 2 pole motor at 100%. It's just heavier from more copper.

Got it!
So with a 7" wheel ill get
5hz - 1.35 m/s
50hz - 13.5 m/s
100hz - 27 m/s

I Will try how it goes and post and update. Thanks to all!

 

[Stacy E. Apelt - Bladesmith]

Welcome Salvador. Glad to have you join us. Fill out your profile so we know where you live and a bit about you.

A 7" wheel sounds right.