How Much Motor Is Enough

B

Brian.Evans

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I'm finalizing my motor choices. I'm building an EERF/GIB type grinder. I will be running a 3hp capable VFD from dealerselectric.

From all the guys that have a direct drive grinder setup and use it a lot, what motor hp did you go with and are you happy with it? Do you wish you'd have spent a bit more and got something larger, or conversely, saved some money and bought something smaller?

Hopefully I can stop planning and start buying soon!
 
2 hp is enough. I have three direct drive VFD grinders, two are 2 hp and one is 3. If I really want to rip some steel, I go to the 3 hp. But really, the 2 hp grinders have plenty of power too and would be fine if that's all I had. I've had a couple of direct drive 1 hp grinders in the past, which I ran direct single speed. I'd only recommend 1 hp if you are running belt speeds of 3000 sfpm or lower. Above that, it seems the torque drops off pretty quickly with speed. I had a Square Wheel with 1.5 hp, which would bog out on the platen- the stock drive wheel was 10", and even with a 1725 motor that's fast.

2hp.
 
+1 Salem.

1.5 leaves you wishing for 3, but it's overkill. I know. ;) 2hp is near perfect for most.
 
My grinding style may be different, but I have a 1.5 Leeson on my KMG and have never had any issues with bogging down. It's not a VFD, but a 3 speed step pulley and I use the middle speed almost exclusively. Anyway, the 1.5 has taken everything I've ever thrown at it without issue.

My most recent grinder was the Fellhoelter horizontal project I have been working on and I did go with a 2 hp motor and VFD for that one. Probably don't NEED the 2hp, but it's nice to have it and not that much more $$. Now that I have a couple of grinders with variable speed I will most likely be upgrading my KMG to a VFD soon and will probably be going with a 2 hp motor for that setup. I don't think 2hp will ever leave you hanging in the knifemaking business.
 
Also keep in mind one motor manufacturers "1hp" is not always equal to anothers "1hp". I've had 1hp motors run pretty weak, and other good name brand ones scream.

I haven't done the vfd thing yet but with direct drive I like them in the 1.5-2hp range. I'm using 1.5hp now, it does the vast majority of tasks fine but when I'm really hogging out metal I could use the 2hp.

My next grinder will be vfd 2hp.
 
ecos said:
Also keep in mind one motor manufacturers "1hp" is not always equal to anothers "1hp". I've had 1hp motors run pretty weak, and other good name brand ones scream.

I haven't done the vfd thing yet but with direct drive I like them in the 1.5-2hp range. I'm using 1.5hp now, it does the vast majority of tasks fine but when I'm really hogging out metal I could use the 2hp.

My next grinder will be vfd 2hp.
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Good point! Exactly why sticking to a trusted manufacturer like Leeson is well advised. You know what you're getting and it's worth it in the long and short run.:thumbup:
 
jonnymac44 said:
Good point! Exactly why sticking to a trusted manufacturer like Leeson is well advised. You know what you're getting and it's worth it in the long and short run.:thumbup:
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Yup, Leeson was actually one of the brands I was very happy with. I've had good luck with Baldor as well.
 
I agree, The type of motor is almost more important than the size. Any 1.5HP of good quality will work. Getting an inverter rated 2HP would probably be the best motor you would want. Above 2HP you are generating more power than you can offer resistance to.

The motor will provide the energy to turn the belt. The HP rating determines how much energy the motor can deliver. If the VFD is good quality and matched to the motor, the torque should be fine even at the upper end. The resistance to this energy determines how much HP you need.
How much steel is in contact with the belt, how hard you lean into the belt, and how coarse the belt is are the only things that control the resistance to the belt moving ( ignoring mechanical loss ).
Two HP is 1100 ft-lb/sec. A 250 pound man pushing a 2" wide piece of steel into a 2" wide 50 grit Norton belt would be nearly impossible to offer enough resistance to slow down the belt noticeably.

The second thing to consider is the power to capability factor. If the grinder is robust, has good enough bearings, and a glass platen, then you can use a bigger motor. If it has caster wheels, skate board bearings, and a mild steel platen, you will be wearing the unit out if you power it with a big motor and really lean in hard when grinding.

So, for any grinder we will need for knife making, a 2HP motor of good make and type with a good quality VFD will deliver all you can use.
If it is a choice in the available motors, get a four pole (1750RPM range) inverter rated 2HP. Of course, TEFC motors and NEMA 4 VFDs are a must .
 
Awesome. Sounds like 1 hp is very very minimal. 1.5 will do, but everyone would rather have 2 for the slight money difference, and 3 is barely worth it.

Thanks everyone.
 
medicevans said:
Awesome. Sounds like 1 hp is very very minimal. 1.5 will do, but everyone would rather have 2 for the slight money difference, and 3 is barely worth it.

Thanks everyone.
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I looked for 2hp motors for a while and had a hard time finding a new one at a fair price in my opinion. I ended up with a new 3hp baldor as a result for the price I would have paid for a 2 hp. Demand of smaller hp motors seems to keep the prices a bit higher than some slightly higher hp motors.
 
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