Grinder selection

Cuchillo59 said:
It was my understanding that doubling the speed for long periods of time would be harmful to the motor. I am not positive on that but I have been reading so much lately that my head is spinning.
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For our applications, I really don't think you'll see much a problem over a reasonable life expectancy of the motor. Thermally, there shouldn't be any issues, as the motor fan will be running twice as fast, so it should even run cooler. You might see some accelerated bearing wear (relative to running at 1800RPM), but also realize the average maker is not going to be running under full load at 3600 for hours upon hours, day in and day out. Depending on manufacturer, it may likely even be the same bearings in both motors, so I'd hazard a guess that this is negligible as well.

Personally, the majority of my grinding is probably around 60% or below, and I only occasionally go full bore if I'm really hogging away at something. I've yet to notice any issues, though my grinder is only a couple years old or so. Others may have better insight. YMMV.
 
Cuchillo59 said:
It was my understanding that doubling the speed for long periods of time would be harmful to the motor. I am not positive on that but I have been reading so much lately that my head is spinning.
Click to expand...
I hadn't read that, but I mostly read on here about motors since I won't be doing full production, just hobby stuff. Pretty sure Stacey's recommendation was 17-1800 and 2X it with a VFD so that's what I went with. I think it'll be fine since you won't be running at 100% all the time.
 
Well I already ordered the 3450 rpm motor , so I guess the next question is should I return it and get the 1725 rpm motor or keep it? I am new to this, would the torque lost be that noticeable in the speeds I will need to grind a knife? I should mention that this will be a hobby for me for now.
 
Here are some numbers regarding the torque on 2 and 4 pole motors at different rpm.

IE2 1.5kW (2HP) 4 Pole AC Motor 230V or 400V

Part Time Output when Inverter powered is:-
5.04Nm, 1.5kW ( 2HP) x 2840 RPM at 100 Hz.
10.09Nm, 1.5kW ( 2HP) x 1420 RPM at 50 Hz.
10.09Nm, 0.75kW ( 1HP) x 710 RPM at 25 Hz.
10.09Nm, 0.15kW (0.2HP) x 142 RPM at 5 Hz.

Continuous Output when Inverter powered is:-
7.2Nm, 1.5kW ( 2HP) x 1988 RPM at 70 Hz.
10.09Nm, 1.5kW ( 2HP) x 1420 RPM at 50 Hz.
8.58Nm, 0.64kW ( 0.85HP) x 710 RPM at 25 Hz.
5.05Nm, 0.08kW (0.1HP) x 142 RPM at 5 Hz.

IE2 1.5kW (2HP) 2 Pole AC Motor 230V or 400V

Part Time Output when Inverter powered is…
2.512Nm - 1.5kW (2.01Hp) x 5700rpm at 100Hz
3.350Nm - 1.5kW (2.01Hp) x 4275rpm at 75Hz
5.03Nm - 1.5kW (2.01Hp) x 2850rpm at 50Hz
5.03Nm - 0.75kW (1Hp) x 1425rpm at 25Hz
5.03Nm - 0.15kW (0.2Hp) x 285rpm at 5Hz

Continuous Output when Inverter powered is…
3.350Nm - 1.5kW (2.01Hp) x 4275rpm at 75Hz
5.03Nm - 1.5kW (2.01Hp) x 2850rpm at 50Hz
4.271Nm - 0.63kW (0.85Hp) x 1425rpm at 25Hz
2.512Nm - 0.07kW (0.1Hp) x 285rpm at 5Hz
 
Thank you Gentlemen for your advice . You will probably hear from me again since I am just a beginner and I want to learn from the best.
 
currenthill said:
Here are some numbers regarding the torque on 2 and 4 pole motors at different rpm.

IE2 1.5kW (2HP) 4 Pole AC Motor 230V or 400V

Part Time Output when Inverter powered is:-
5.04Nm, 1.5kW ( 2HP) x 2840 RPM at 100 Hz.
10.09Nm, 1.5kW ( 2HP) x 1420 RPM at 50 Hz.
10.09Nm, 0.75kW ( 1HP) x 710 RPM at 25 Hz.
10.09Nm, 0.15kW (0.2HP) x 142 RPM at 5 Hz.

Continuous Output when Inverter powered is:-
7.2Nm, 1.5kW ( 2HP) x 1988 RPM at 70 Hz.
10.09Nm, 1.5kW ( 2HP) x 1420 RPM at 50 Hz.
8.58Nm, 0.64kW ( 0.85HP) x 710 RPM at 25 Hz.
5.05Nm, 0.08kW (0.1HP) x 142 RPM at 5 Hz.

IE2 1.5kW (2HP) 2 Pole AC Motor 230V or 400V

Part Time Output when Inverter powered is…
2.512Nm - 1.5kW (2.01Hp) x 5700rpm at 100Hz
3.350Nm - 1.5kW (2.01Hp) x 4275rpm at 75Hz
5.03Nm - 1.5kW (2.01Hp) x 2850rpm at 50Hz
5.03Nm - 0.75kW (1Hp) x 1425rpm at 25Hz
5.03Nm - 0.15kW (0.2Hp) x 285rpm at 5Hz

Continuous Output when Inverter powered is…
3.350Nm - 1.5kW (2.01Hp) x 4275rpm at 75Hz
5.03Nm - 1.5kW (2.01Hp) x 2850rpm at 50Hz
4.271Nm - 0.63kW (0.85Hp) x 1425rpm at 25Hz
2.512Nm - 0.07kW (0.1Hp) x 285rpm at 5Hz
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So you'll get a little more than twice the torque for the same lower end RPMs on an 1800RPM (I.E. 4 pole) motor vs the 3600RPM (2 pole). Strictly speaking in terms of Hz (VFD frequency), the 4 pole motor will run half as fast but have twice the torque for the same frequency on a 2 pole motor.

In the end, I suppose it depends on how you want to grind. Some makers like having that extra boost in speed and compensate the lower torque with a higher HP motor, others, like myself, tend to grind a little slower more often than not, and do well enough with the torque from the 2hp.

I should add that I do use a 5 inch drive wheel vs the "standard" 4 inch, which yields a few more SFPM (not to be confused with RPMs of course) vs a smaller drive wheel.
I suppose surface feet per minute (SFPM) probably shouldn't be left entirely out of the discussion either....
 
To bring the discussion back to the OP's question of which grinder is best for his needs...

I suspect that both the Northridge and the Ubergrinder are at the very top tier of what's available in a 2x72 machine, for the money. I'd definitely get a horizontal capable machine no matter what, and for this tier of machine (price, quality, features, etc...) it's really hard to say if one is "better" than the other, and you could probably even throw the TW-90 into the discussion at this point.

It's not really that any of the three aforementioned machines will do something that one of the others can't, or grind a better knife or be easier to use... it will ultimately just boil down to final cost (which may only be $100-$200 different when you boil down all of the features, shipping, etc..., I have not recently priced any of them...) and some minor differences in design and functions of things like work rests, platens, and other little attachments.

Bottom line: which one grinds the best knife? You do.
 
gunfixrjoe said:
Thanks to all that have suggestions. Thinking I'll look into the TW90 a bit more....
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One thing that pops out at me is the price of the Northridge without the tilt feature is 1K less money but you add the Tilt, Rat Arm, and Baldor motor and the price goes up that GRAND seems a little steep just to get the Upgrade. The TW-90 has the built in tilt but comes with every accessory including the small wheel attachment.
 
TW 90 is a great machine. Service and support are so important. My TW90 arrived with a bent support arm on the motor. I contacted Travis, he suggested how to straighten it to use until he could get another entire setup to me. He sent the return tag and packing material with the new one. That IMO was outstanding service.
 
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