Grinder in a box motor questions..

B

BellyUpFish

Joined
Mar 30, 2012
Messages
86
Hey guys-

I'm planning on building a GIB and am looking at motors.

1700ish vs 3400ish rpm seem to be the choices.

I'm looking at a 2hp motor, as I won't be making a bunch of knives and will be using this more with other metal work I find myself doing.

I'll be running a Teco FM50, most likely.

So, I'm stuck on the motor speed.

I'm thinking 3450rpm sounds better for speed, but the 1700rpm should have more torque and part of me thinks this is better for a grinder?

Anyone?
 
Here is my opinion. I just built a GIB and set it up to grind horizontal. I think a 1725 RPM is too slow with a 4 or even 5 inch drive wheel. The problem is that even if you could have a larger drive wheel made it would be too close to the base plate to get your belts on it easily. Some people will tell you that you can double the speed with your VFD although I do not know if the Teco will let you do this. Bob Frink who builds KMG grinders advises that you not double the speed with your VFD. I may be wrong but I think Travis Wuertz uses a speed doubling VFD on his TW-90 grinder and I think that other builders of grinders do this as well. I put a 2 hp 3 phase Leeson 3450 RPM motor on mine with a 4 inch drive wheel and it produces about 3613 surface feet per minute which is plenty fast from my experience. Maybe Brett Mathews will have some advice because he builds the very popular Esteem grinder that is direct drive. Larry
 
Seems like running high speed, at a higher horsepower should do what I'm looking for.

I fabricate as much as I can, but I'm not rebuilding dump trucks or anything.
 
I have a 2hp Weg 3400rpm motor on my GIB. I run it with a KBAC27D VFD. I want more at both ends of the SFPM spectrum. I'm currently running a 4" drive wheel and it does well but I know that more speed would help my ceramic belts perform better. The problem is, I also need better slow speed control. My machine starts stuttering down around 30%. I need to be able to grind down to about 500-600sfpm but right now 800-1000 is about as low as I can get. I am seriously considering switching to a 1700rpm motor and overdriving it with the VFD and running a 5" drive wheel.

Bob
 
Bob, I'm not exactly sure what this 2X jumper does on KABC drives, but I suspect it simply allows setting max RPM from 60 hz to 120 hz. Just because it's set to allow 120 hz (double speed), doesn't mean you have to run it that fast. The drive I'm using doesn't have a "jumper" to change, it's just a software setting which I have set to 70hz giving me about 4,000 RPM max on my 3450 RPM motor. With a 4" drive wheel this gives a bit over 4K SFPM belt speed. I can easy grind gently at 500 SFPM, so it fills my needs. When you say "starts stuttering down around 30%", do you mean actually dropping out? It might have min speed set at that point. I set my VFD to drop out at 10hz.

If you want more upper and lower speeds, try a 3" drive wheel with the 2X jumper in place. That would give you a good range of belt speeds of around 600 SFPM (25%) to 5,500 SFPM (about 2X) . Might be less expensive to try a different drive wheel than changing motors?

Just a side note here, you mention using a 1725 RPM motor and a 5" drive wheel. Using the 2X jumper for doubling the speed at 120 hz would give you the same 3450 RPM you've got now for a max speed of around 4500 SFPM?

Ken H>
 
I like 1750rpm motor with step pulleys or variable speed and sharp fresh Ceramic belts.

Speed doesn't make up for worn belts. If your grind or even finish your knives after HTment you want slower speed and new belts or you can ruin the temper of the knives.
 
High speed is used once for every ten times slow speed is used. Go with 1750, and you will be much happier.
 
BellyUpFish said:
I won't be grinding many knives, but it'll be used for general shop use.
Click to expand...

For any work where finishing is concerned you want SLOWER! For belts of about 220 up you will find a sweet spot in the speed that the belt with cut and finish properly in. Generally, the higher the grit, the slower you want the belt turning.
 
As the other folks said, depending on grit belt you think you'll be using most. For general shop grinding - is this "hogging" metal general use? If so, the 36 grit will be used a lot and high speed. I personally find the 3450 RPM motor a better fit for 500 to 4,000 SFPM belt (4" drive wheel) speeds without having to over speed the motor so much. Also the 3450 RPM 3 ph motor is a bit less expensive than a 1725 rpm motor since it only has 2 poles. I think it was $127 shipped for a 3450 RPM TEFC 2 hp motor vs $166 or so for the 1725 rpm.

Ken H.
 
Ken - what motor are you using? Do you have a link?

I've been looking for a good price on a Baldor or Leeson.
 
Ken H> said:
Well, Baldor or Leeson are both good motors, I've got a 1hp 3ph Leeson on my lathe, but this time I opted for an Iron Horse motor due to cost. Look at bottom of this link for 2hp motors:

http://www.automationdirect.com/adc..._(0.33_-_2HP)/3-Phase_Motors,_56C_(0.33_-_2HP)
Click to expand...

I've found a used Baldor for $150, but it's used, so no telling how it's been treated. I think if I were patient I could find a new-surplus for around $200, from what it looks like..

I'd really rather source a "new" motor, as I'm just skeptical on some used equipment.

Are you happy with the Iron Horse?
 
Last edited:
Sure Iron Horse motors are just fine - note the price difference in 1725 rpm vs 3450 rpm due to the 2 pole vs 4 pole motor construction. The 60 hz power line freq is what determines number of poles for RPM. A new Baldor 1725 for $200 is not a bad price at all.
 
Bob, I bought a 3450 motor for my GIB because of your experience with it. I do not have the stalling problem that you speak of. I am wondering if you can make some adjustment to your drive because I have the same drive and set my adjustment controls according to the instructions on the Beaumoint Metal works website for wiring a 2 hp motor. They are more specific if my memory serves me than the instructions for adjustments in the KBAC 27-D manual. Larry
 
Yes, if you can get the Baldor3450 rpm motor for a decent price then I would do that. I only use mine to grind knives but with the variable speed you could grind any metal. Larry
 
You must log in or register to reply here.
Back
Top