Electric motor brands

[Eddyde]

Do you need a 2 hp motor for 2” wide sander? I have a 1hp motor on my 6x48 sander and never felt it was lacking any power.

 

[projectnut]

Come to think of it my Rockwell Delta 6x48 sander only has a 1-1/2 hp motor on it. I push it pretty hard and have never had it bog down or stall

 

[matthewsx]

This is the kind of feedback I'm looking for. I've thought about using a lower hp motor, but would hate to have it come up short in the long run. I'm looking at 2hp because that's what the knife guys say is minimum.

I was looking at some US Motors brand too, just hard to spend an extra $100 if I don't need to.

John

 

[metalmagpie]

I submit that the size and rpm of your motor should be calculated from the actual requirements of your grinder. For roughing with a coarse belt, many belt makers recommend 6000 feet/minute belt speed. To run very high grit belts at 6000 sfm would shred them quickly. For e.g. a 1200 grit belt, you want something like 600 sfm. So a good design goal is 600-6000 sfm.

The belt sfm is proportional to the drive wheel diameter. SFM = PI * DIAM * RPM / 12
as long as your drive wheel diameter is in inches.

If you have a 6" drive wheel then your belt speed will be 1.57 * RPM. If you plug in 1750 for rpm you get about 2750 sfm. If you overspeed your motor to 120 Hz (about the limit of what you can do safely) you get to 5500 sfm. That's why you might consider a 3450 rpm motor.

As for size, you want as much hp as you can afford. Be aware that a 3hp VFD is quite a bit spendier than a 2hp VFD. And of course the bigger motor costs more. Also, your grinder is probably designed with a range of motor frame sizes in mind. If you buy too big a motor you may have to modify your grinder so the motor will fit.

Finally, if your grinder has the modern feature of being able to swivel the platen 90 degrees, a big motor may make that into a seriously muscular event.

I recommend a 2hp 3450 rpm 143 frame motor for a 2x72" belt grinder. I built one in 2011 which had a 3hp motor and I doubt I ever needed it.

BTW when you are really roughing be sure you have a spark catcher of some kind else you may literally catch your shoes on fire.

metalmagpie

 

[projectnut]

Burr King grinders are top of the line. They use either a 1hp or 1-1/2 hp motor depending on the size and style. I’ve ever seen one stall out. I think you’ll break the belt long before you bog down or stall out the motor

 

[Eddyde]

I suppose if you are going to regulate the speed with a VFD, a little extra horsepower would help retain more low-end torque.

 

[matthewsx]

If I had a bigger shop with more space to tear stuff down I’d try adapting a treadmill motor. As it stands I’ve mounted the grinder on one half of my old lathe stand which will make it compact and portable.

I did have a plan to use a big 5hp motor I already have but will take up too much space.

If I could get away with a 1hp 3450 rpm that’ll bring the price way down.

John

 

[matthewsx]

I submit that the size and rpm of your motor should be calculated from the actual requirements of your grinder. For roughing with a coarse belt, many belt makers recommend 6000 feet/minute belt speed. To run very high grit belts at 6000 sfm would shred them quickly. For e.g. a 1200 grit belt, you want something like 600 sfm. So a good design goal is 600-6000 sfm.

The belt sfm is proportional to the drive wheel diameter. SFM = PI * DIAM * RPM / 12
as long as your drive wheel diameter is in inches.

If you have a 6" drive wheel then your belt speed will be 1.57 * RPM. If you plug in 1750 for rpm you get about 2750 sfm. If you overspeed your motor to 120 Hz (about the limit of what you can do safely) you get to 5500 sfm. That's why you might consider a 3450 rpm motor.

As for size, you want as much hp as you can afford. Be aware that a 3hp VFD is quite a bit spendier than a 2hp VFD. And of course the bigger motor costs more. Also, your grinder is probably designed with a range of motor frame sizes in mind. If you buy too big a motor you may have to modify your grinder so the motor will fit.

Finally, if your grinder has the modern feature of being able to swivel the platen 90 degrees, a big motor may make that into a seriously muscular event.

I recommend a 2hp 3450 rpm 143 frame motor for a 2x72" belt grinder. I built one in 2011 which had a 3hp motor and I doubt I ever needed it.

BTW when you are really roughing be sure you have a spark catcher of some kind else you may literally catch your shoes on fire.

metalmagpie

I currently have a 3" drive wheel so using your calculation I'd have 2708 sfm for a 3450 rpm motor. If I cut the speed down 50% I'd still be at 1354 SFM so I'd need to drive that motor at 25% to get into the lowest range you're recommending. I could buy a bigger drive wheel but that would add more $$.

This might make sense but how would it affect the torque, and would it increase the load on the motor appreciabily?

The 1800 rpm motor gets me closer to optimum without loosing too much from the VFD. Want to get this right if at all possible, but don't really want to get over $500 invested total.

John

 

[akjeff]

I went with a 2hp Dayton( 3450 rpm ) when I built my 2x72 grinder. No regrets, it eats metal! I'd much prefer too much motor, than too little. With a 5" drive wheel, and the TECO 510 drive set at 60hz, it's at roughly 4500 SFM.

 

[matthewsx]

What do you guys think about this one?

New (Custom) Motor 1725RPM 1.5HP 208-230/460V 60Hz 3Ph 5.3A 56C | eBay

Motor is new, open-box, packaging was opened to confirm contents and provide detailed photos. Includes a 30 day guarantee.

www.ebay.com