Belt grinder motor question

B

Brekfast

Joined
Dec 9, 2005
Messages
57
Hello,


In most posts I have read on this subject, belt grinders were described using 1-2 hp 1725 rpm TEFC motors.

My question is, 3450 rpm motors are not good for this application ? Also, what if the motor has more than 2 hp, say 5 or even 7, would that make it unsafe/unusable to serve as a beltgrinder motor ?

Oh and one other question, what is the significance of whether the motor has 1 phase or more ?

Thank you.

Henrik
 
Henrik, The sanding you will be doing works better at lower speeds.That is why variable speed grinders are popular.You use higher speeds with coarse belts and slow speeds for fine belts.If you don't have variable speed capabilities, use a lower single speed.
Bigger HP is only an issue with the extra power draw. Almost all homes only have single phase power, as 3 phase is industrial.3 phase can be done with phase converters or VFD's.This is a good way to go if you can afford it.3 phase motors are cheaper and more efficient but require additional equiptment.VFD's will do this and give you variable speed as well.I hope this helps. Dave:)
 
Speed control can be as simple as using different size pullies to slow down the driving contact wheel. Slowing down a 3450RPM motor by 50% will increase the amount of torque that you have available without affecting the HP.

I run all my knives on a single speed 1750 RPM grinder with a 14" driving wheel(14"diameter X 3.14 Pi X 1750 RPM X60 min per hour) / 63360 inches per mile= about 73 miles per hour belt speed. It runs on a 7.5 HP motor. It also does all my buffing.

I grind hundreds of knives per year so am convinced that there is no substitute for Horsepower.
 
Most step pulley, or direct drive set ups 2X72 grinders come with are meant for use with 1725 rpm motors. They're set up to operate over the normal speed range most folks use when driven at 1725 rpm. If you go to the faster motor, you will either have to live with the higher speed, or come up with your own method of slowing it down.

More horsepower is always nice, but for the most part 2hp or so is probably all you'll ever need. My grinder is 1.5hp and I have to really lean into it before it even acts like I'm working it hard. I've never been able to slow it down or stall it.
 
Thank you very much for the explanations. I saw a Baldor 7.5hp 3450rpm tefc
motor on Ebay and was considering buying it. From what you have explained I better get something with 1750 rpm then.

I guess a DC motor would be also better since eventually it could accept a speed controller.

Thanks again for clearing this up for me.

Henrik
 
I don't think its eventually for the speed controller, I think you have to have one from the start. If nothing else, it will have to have an inverter to run off house hold current, and there are some other issues as well. If I remember correctly you have to have a resistor in the circuit to act as a break, and limit the motor's speed as well.
There are usually treadmill motors for sale on ebay for cheap, so the dc motor idea is tempting, but remember to look into the cost of controllers also.
 
I guess I am chicken but I have a 1 HP motor on my home made machine.
My driver wheel is a measly 7" dia. so I guess you will fall on the ground laughing George.;)
Still, I figured that for a beginner it was ample. The design is such that I can change the pulley to whatever I want and the motor too for that matter.
When I grind a big blade it takes a bit long but I have never stopped the motor, even with good force.
As a beginner high speed=much less reaction time when things go wrong and I have found that even at my low speed a screw up still happens far too quickly.:eek:

Henrik, I got your pm, I will call you soon.Good luck with your decision of motor.
One thing to consider though when buying from evilbay, a motor is quite heavy and it is very likely that the one you buy will come from the US, the shipping might cost a lot.
You might want to look in the yellow pages for second hand motor dealers.
I bit the bullet and bought a new one for $200CAD and I have no regrets.

Mike
 
Well,

I came across a HVAC 1.5 hp, TEFC, variable torque, 1740 rpm Baldor motor for a very reasonable amount and bought it.

Not sure what the variable torque means when using it on a grinder though
......

Hope it will be ok


Henrik
 
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